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Engineering Manual Geotechnical
TRACK DRAINAGE
Version 1.2 Issued December 2009
Owner:
Principal Engineer Geotechnical
Approved by: John Stapleton Group Leader Standards Civil
Authorised by:
Jee Choudhury
Principal Engineer
Disclaimer This document was prepared for use on the RailCorp Network only. RailCorp makes no warranties, express or implied, that compliance with the contents of this document shall be sufficient to ensure safe systems or work or operation. It is the document user’s sole responsibility to ensure that the copy of the document it is viewing is the current version of the document as in use by RailCorp. RailCorp accepts no liability whatsoever in relation to the use of this document by any party, and RailCorp excludes any liability which arises in any manner by the use of this document. Copyright The information in this document is protected by Copyright and no part of this document may be reproduced, altered, stored or transmitted by any person without the prior consent of RailCorp
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Engineering Manual
TMC 421
RailCorp Engineering Manual — Geotechnical Track Drainage
TMC 421
Document control Revision
Date of Approval
Summary of change
1.2
December 2009
1.1
October 2007
C4.2.3.2: change to minimum pipe slope as per ESC 420; C4.6.1 Table 6: deleted details relating to drain slope of 1 in 300, Flowcharts 2 and 3 updated for change in minimum slope, Form 2 section (f): minor changes to wording; inclusion of Duration Interpolation Diagram 2.1.
1.0
October 2006
First issue as a RailCorp document. Replaces RTS 3432 and RTS 3433
Changes detailed in chapter revisions
Summary of changes from previous version Chapter
Current Revision
Control pages
1.1
Change of format for front page, change history and table of contents
1
1.1
Format change only
2
1.1
Format change only
3
1.1
Format change only
4
1.1
Format change; changes to be consistent with ESC 420 V2.0
5
1.1
Format change only
6
1.1
Format change only
7
1.1
Format change only
App 1
1.1
Format change only
App 2
1.1
Format change only
App 3
1.1
Format change only
App 4
1.1
Format change only
App 5
1.1
Format change only
App 6
1.1
New
App 7
1.1
New
© Rail Corporation Issued December 2009
Summary of change
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RailCorp Engineering Manual — Geotechnical
Track Drainage
TMC 421
Contents Chapter 1 C1-1 C1-2 C1-3 C1-4 Chapter 2 C2-1 C2-2 Chapter 3 C3-1 C3-2 C3-3 Chapter 4 C4-1 C4-2 C4-3 C4-4 C4-5 C4-6 C4-7 Chapter 5 C5-1 C5-2 C5-3 C5-4 C5-5 C5-6 C5-7 Chapter 6 C6-1 C6-2 C6-3 C6-4 C6-5 Chapter 7 C7-1 C7-2 C7-3 C7-4 C7-5
Introduction to Manual ............................................................................................................. 4
Purpose....................................................................................................................................... 4
How to read the Manual.............................................................................................................. 4
References.................................................................................................................................. 4
Definitions, abbreviations and acronyms .................................................................................... 4
General Requirements.............................................................................................................. 5
Introduction ................................................................................................................................. 5
Competencies ............................................................................................................................. 5
Types of Track Drainage .......................................................................................................... 6
Introduction ................................................................................................................................. 6
Surface Drainage ........................................................................................................................ 6
Subsurface Drainage .................................................................................................................. 8
Design of Track Drainage....................................................................................................... 17
Introduction ............................................................................................................................... 17
Design Criteria .......................................................................................................................... 17
Design Investigation.................................................................................................................. 23
Estimation of the Required Drainage System Capacity............................................................ 25
Surface Drain Design................................................................................................................ 27
Subsurface Drain Design .......................................................................................................... 33
Other Design Considerations.................................................................................................... 37
Construction of Track Drainage ............................................................................................ 38
Line and Grade ......................................................................................................................... 38
Site Preparation ........................................................................................................................ 39
Excavation................................................................................................................................. 39
Surface Drain Construction....................................................................................................... 40
Subsurface Drain Construction ................................................................................................. 40
Other Types of Construction ..................................................................................................... 44
Inlets and Outlets ...................................................................................................................... 44
Maintenance of Track Drainage............................................................................................. 46
General ..................................................................................................................................... 46
Surface Drainage ...................................................................................................................... 47
Subsurface Drainage ................................................................................................................ 49
Typical problems and solutions.................................................................................................50
Preparation for Flooding ........................................................................................................... 55
Documentation Requirements............................................................................................... 57
Introduction ............................................................................................................................... 57
Review Process ........................................................................................................................ 57
Drawing requirements............................................................................................................... 58
Hydrology/Hydraulic Report requirements................................................................................ 60
External party development discharging onto or through the rail corridor................................ 61
Appendix 1
Flow Charts.............................................................................................................................. 63
Appendix 2
Drainage Design Checklist..................................................................................................... 66
Appendix 3
Design Investigation Form..................................................................................................... 72
Appendix 4
Calculation of Capacity Required Form ............................................................................... 74
Appendix 5
Drawings: Typical Examples ................................................................................................. 78
Appendix 6
Approved Track Drainage Products ..................................................................................... 80
Appendix 7
R Loading Configuration........................................................................................................ 82
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TMC 421
Chapter 1 Introduction to Manual C1-1
Purpose The purpose of this manual is to provide a comprehensive guide for the design, construction and maintenance of effective track drainage. Regular examination, inspection and routine maintenance of drainage systems is essential in maintaining the integrity of the track formation, supporting embankments and cuttings. Neglect of drainage problems will inevitably lead to track problems. Inspection of track drainage is included in Track Engineering Manual TMC 203.
C1-2
How to read the Manual When you read this manual, you will not need to refer to RailCorp Engineering Standards. Any requirements from standards have been included in the sections of the manual and shown shaded. The shaded sections in this Manual are extracts from RailCorp Standard ESC 420 “Track Drainage”. Reference is however made to other Manuals.
C1-3
C1-4
References TMC 203
Installation & Maintenance Manual – Track Inspection
TMC 411
Earthworks Manual
AS 3706
Geotextiles – Methods of test
AS 3725
Loads on buried concrete pipes
AS 5100
Bridge design
Institution of Engineers Australia
Australian Rainfall & Runoff 2001
ED 0022P
RailCorp CAD & Drafting Manual – All Design Areas
ED 0026P
RailCorp CAD & Drafting Manual – Track
ED 0027P
RailCorp CAD & Drafting Manual – Bridges & Structures
CV 0400998
Ballast Cage (Lobster Pot) with Removable Lid
CV 0497068
Pipe Culverts Headwalls to Suit Pipes 225-600mm Diameter
CV 0497069
Pipe Culverts Headwalls to Suit Pipes 675-1800mm Diameter
Definitions, abbreviations and acronyms Cess drain:
located at formation level at the side of the track
Catch drain:
intercepts overland flow or run-off before it reaches the track and related structures such as cuttings or embankments
Mitre drain:
connected to cess and catch drains to remove water or to provide an escape for water from these drains
Multiple tracks:
more than 2 tracks
Track drainage:
drainage of the track formation including diversion of water away from cuttings and embankments
Site supervisor:
a qualified civil engineer or a competent person with delegated engineering authority for drainage construction.
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TMC 421
Chapter 2 General Requirements C2-1
Introduction This manual specifies the design, construction and maintenance requirements for track drainage systems. It covers drainage of the track formation, supporting embankments and cuttings. This manual does not cover drainage from platforms, buildings, overbridges, footbridges, airspace developments, external developments, access roads, roads outside the rail corridor, Council drains or properties adjacent to the rail corridor. Track drainage is to be designed to capture water flows calculated in accordance with this manual. No other drainage is to be discharged into the track drainage system without the approval of the Chief Engineer Civil.
C2-2
Competencies The design of track drainage shall only be undertaken by a suitably qualified engineer with competency in track drainage design and with delegated Engineering Authority for track drainage design. The construction of surface and subsurface drainage shall only be carried out under the supervision of a Site Supervisor.
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Chapter 3 Types of Track Drainage C3-1
Introduction Without adequate track drainage, track formation may become saturated leading to weakening and subsequent failure. Formation failure may be indicated by any of the following; mud pumping up through the ballast, repeated top and line problems, bog holes, or heaving of the formation. If the permanent way or track structure is to be maintained at a suitable standard for the passage of freight or high-speed passenger trains, adequate drainage must be installed in new or upgraded track, and existing drainage must be maintained so that it works effectively. Track drainage consists of two types:
C3-2
−
Surface drainage
−
Subsurface drainage.
Surface Drainage Surface drainage removes surface runoff before it enters the track structure, as well as collecting water percolating out of the track structure. Basic grading of the ground on either side of the track is a form of surface drainage, and allows water flowing out of the track structure to be removed. Shoulder grading may be used in very flat areas where it is difficult to get sufficient fall for either surface or subsurface drains. Shoulders graded to fall away from the track formation
Figure 1 Typical Track Formation There are three main types of surface drainage. These are:
−
Cess drains
−
Catch drains
−
Mitre drains.
Figure 2 Surface Drainage Types © Rail Corporation Issued December 2009
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C3-2.1
TMC 421
Cess Drains Cess drains are surface drains located at formation level at the side of tracks, to remove water that has percolated through the ballast and is flowing along the capping layer towards the outside of the track formation. Cess drains are primarily intended for the protection of the formation by keeping the formation dry. Cess drains are most frequently found in cuttings where water running off the formation cannot freely drain away. C
C
Cess drain
30
1
Figure 3 - Cess drain - Typical location Surface drains can be constructed on fairly flat grades, as they are easily cleared of any sediment that may collect in them.
C3-2.2
Catch Drains The purpose of catch drains (also known as top drains) is to intercept overland flow or runoff before it reaches the track. They reduce the possibility of causing damage to the track or related structures, such as cuttings or embankments. Catch drains are generally located on the uphill side of a cutting to catch water flowing down the hill and remove it prior to reaching the cutting. If this water was allowed to flow over the cutting face, it may cause excessive erosion and subsequent silting up of cess drains.
Figure 4 – Typical catch drains Catch drains may be used alongside tracks that cut across a slight downhill grade.
C3-2.3
Mitre Drains Mitre drains are connected to cess and catch drains to provide an escape for water from these drains. Mitre drains should be provided at regular intervals to remove water before it slows down and starts to deposit any sediment that it may be carrying.
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Figure 5 - Mitre drains
C3-3
Subsurface Drainage Subsurface drainage is necessary for maintaining the integrity of the track formation and ensuring
the stability of earth slopes.
Subsurface drainage is used for:
−
drainage of the track structure
−
controlling of ground water
−
the draining of slopes.
Subsurface drainage shall be provided in locations where the water table is at or near earthworks level.
Subsurface drainage shall be provided along the cess, between, across, or under tracks as
required.
Advice should be sought from the Principal Geotechnical Engineer before designing and installing
sub-surface drainage.
Subsurface drainage systems shall be designed to take surface runoff, ground water and seepage,
and water collected from other drainage systems to which the new system is being connected.
Most systems will only have to cater for surface runoff.
If a drainage system is required to remove ground water and seepage, a detailed hydrological and
geotechnical investigation is required to determine the volume of water for the sizing of drains.
The volume of water from other systems is determined from the outlet capacity of that system.
Subsurface drains are used where adequate surface drainage cannot be provided due to some
restriction or lack of available fall due to outlet restrictions. Locations where these circumstances
may occur are:
−
Platforms
−
Cuttings
−
Junctions
−
Multiple tracks
−
Bridges
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TMC 421
Functions of Subsurface Drains Subsurface drainage systems perform the following functions: −
Collection of infiltration water that seeps into the formation (capping layer), as shown in Figure 6.
−
Draw-down or lowering of the watertable, as illustrated in Figure 7.
−
Interception or cut-off of water seepage along an impervious boundary, as illustrated in Figure 8.
−
Drainage of local seepage such as spring inflow, as shown in Figure 9.
Rainfall
C
1
30
Capping layer Collector drains
Figure 6 - Collection of water seeping into the ballast structure. Original ground level
C
Cutting slope Original watertable 30
Draw-down drain
1
Watertable
Draw-down drain
Figure 7 - Lowering the watertable.
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Geotextile Seepage Zone
Aggregate Filter Slotted Pipe
Type 1: Aggregate, geotextile and slotted pipe drain
Trench backfilled with excavated material
Geotextile drain Seepage Zone
Slotted Pipe Type 2: Geotextile drain
Figure 8 - Interception and cutoff of seepage water.
Cutting face
Connecting to either ditch or pipe drain Plan showing location of seepage drains
Geotextile Aggregate Slotted pipe Slotted pipe
Section A-A A C 20
1
A
Section A-A - Seepage drain
Figure 9 - Drainage of local seepage.
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C3-3.2
TMC 421
Types of Subsurface Drains Subsurface drains normally used for track drainage can be classified into three types according to
their location and geometry:
−
Longitudinal drain (Figure 10).
−
Transverse drain (Figure 11).
−
Drainage blankets (Figure 12).
Sump Cutting
A
Up track
A
Down track Longitudinal drain
Catch Drain
C
Capping layer Aggregate Geotextile Slotted pipe Section A-A
Figure 10 - Typical longitudinal drain arrangement. C
Geotextile if required Side of excavation
Compacted fill
Rock protection for pipe outlet Free draining rockfill
Slotted pipe
Figure 11 - Typical transverse drain.
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Geotextile
Drainage blanket Spall protection
Figure 12 - Typical drainage blanket. Two other types of subsurface drainage are: −
Horizontal drains (Figure 13).
−
Vertical drains (Figure 13).
Unstable soil
Excavation
Embankment Watertable Permeable blanket
Horizontal drain Vertical well drains
Figure 13 - Typical horizontal and vertical drain arrangement. Horizontal and vertical drains are more specialised and are seldom used for track drainage. Horizontal drains are generally used to drain wet soils and speed consolidation of earth structures. Vertical drains may also be used to speed consolidation. Another type of vertical drain is used to drain water from behind retaining walls or bridge abutments.
C3-3.3
Subsurface Drain Material Types Subsurface drains may also be classified according to the materials used in the drain. For example: −
Aggregate drains
−
Pipe drains
−
Geotextile drains
−
A combination of the above.
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TMC 421
Aggregate Drains These drains consist of permeable granular material. The aggregate should be coarse enough to be free draining, but not so coarse as to allow the migration of fines into or through the permeable material. The graded aggregate is to be wrapped in a geotextile (Figure 14).
Graded aggregate
Subsoil
Geotextile filter
Figure 14 - Cross-section of an aggregate drain.
C3-3.3.2
Pipe Drains These consist of perforated or slotted pipes, installed by trenching and backfilling. Some type of filter material around the pipe or permeable backfill is normally required to minimise clogging of the drain perforations or slots (see Figures 15, 16 & 17).
Graded aggregate
Impervious Subsoil
Geotextile filter Slotted pipe
Figure 15 - Cross-section of a typical subsoil drain used in impervious soil (eg clayey soils) Geotextile overlap
Graded aggregate Geotextile filter
Pervious Subsoil
Slotted pipe
Figure 16 - Cross-section of a typical subsoil drain used in pervious soil (eg sandy soil).
Capping Impervious Subsoil Pervious fill Geotextile filter Slotted pipe
Figure 17 - Cross-section of a subsoil drain where the pipe is wrapped in geotextile. (Alternative slotted pipe system)
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C3-3.3.3
TMC 421
Geotextile Drains A geotextile drain may be a horizontal, vertical, or inclined blanket whose purpose is to collect subsurface water and convey it along the plain of the fabric to an outlet. The drain must also act as a filter to keep soil particles out of pores and prevent clogging. An example is shown in Figure 18. Vertical geotextile drain
Retaining wall
Horizontal geotextile drain (optional)
Backfill Collector pipe
Figure 18 - Geotextile drain behind a retaining wall. A similar arrangement may be used behind bridge abutments.
C3-3.3.4
Other Types of Subsurface Drain Where large volumes of water may need to be removed by subsurface drains, a carrier pipe may be used in conjunction with a collector drain, as shown in Figure 19. With this arrangement the collector drain does not need to carry all the water. The advantage of this arrangement is that excess (large volumes) water is removed from the collector drain thus preventing it seeping into the subgrade again at a point further down the drainage route. Figure 19 shows a typical arrangement for a collector drain and carrier pipe located between two tracks. The subsurface water is collected by the collector drain between the two sumps shown, it is then conveys water to the down stream sump where it can enter the carrier pipe and be removed without any risk of it re-entering the subgrade. See Figure 33 for an example of this system used in yard drainage.
Sump cage
Subsoil drain (collector)
Sump Sump Carrier pipe
Figure 19 - Subsoil collector drain plus a larger carrier pipe
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C3-3.4
TMC 421
Inlets and Outlets There are various types of inlets and outlets in use for subsurface drains. The main purpose of inlet and outlet protectors is to reduce erosion. Where outlet velocities are expected to be high, some form of energy dissipater should be installed. Also, where the sediment load of the water being discharged from a drainage system is high, a silt trap should be installed (see Figure 20 below). Rectangular Silt Trap collects deposited silt and is easily cleaned
Figure 20 - Typical silt trap installed in drains with high sediment loads. Some typical examples of inlet and outlet protection are:
−
Precast concrete units
−
Grouted sand bags (Figure 21)
−
Concrete (Figure 22)
−
Reno mattresses and gabions (Figure 23)
−
Revetment mattress (Figure 24)
−
Spalls grouted or hand packed (Figure 25)
Pipe outlet
Grouted sand bags
Figure 21 -Grouted Sand Walls.
Pipe outlet
Concrete headwall
Figure 22 - Concrete Headwall.
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Cut-off wall
Figure 23 - Gabion Headwall.
Wire basket headwall and mattress apron, Used mainly for larger pipe outlets
Figure 24 - Revetment Mattress.
A typical arrangement of hand packed walls. Cut-off wall should be provided at the bottom of the headwall to prevent the wall being scoured out and washed away, particularly on the down stream side.
Figure 25 - Spalls used as a Headwall.
NOTE: As mentioned in Figure 25, on the down stream side of the outlet, water getting under the headwall structure and causing scouring and the eventual washaway of the headwall is a problem that must not be overlooked. The best way to help prevent this occurring is to provide a cut-off wall at the end of the headwall (see Figure 23 for an example).
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TMC 421
Chapter 4 Design of Track Drainage C4-1
Introduction The purpose of this section is to specify design criteria and the design process to enable track and related structures to be drained effectively using either surface or subsurface drainage systems. Proper drainage design, using the design process detailed in this section, may allow problems to be discovered early and enable easier construction. Only staff with the appropriate RailCorp Engineering Authority shall carry out the design of track drainage. This section discusses the design process from the initial concept through to the detailing of the drain capacity and components required. Flow charts of the design process are provided in Appendix 1. A drainage design checklist is provided in Appendix 2.
C4-2
Design Criteria
C4-2.1
General Drainage systems are to be designed for the peak capacity calculated by the Rational Method. The Average Recurrence Interval (ARI) shall be 50 years. Proposed variations to the design ARI due to site constraints or other factors shall be supported by a risk assessment and shall be approved by the Chief Engineer Civil. The minimum design life of all track drainage components shall be 50 years with consideration given to site location and groundwater conditions. The following configurations are not approved for track drainage on the RailCorp network: −
plastic pipes: unplasticised polyvinylchloride (UPVC); polypropylene
−
inverted syphon systems.
Drainage cell systems shall only be used with the approval of the Principal Engineer Geotechnical.
C4-2.2
Surface Drainage
C4-2.2.1
Cess Drains The flow capacity of the open channel cess drain shall be greater than the peak flow rate. For ease of maintenance, over sized channels can be adopted to allow a certain degree of sediment build up to occur and still work effectively. Type 2 - Rectangular
Type 1 – Trapezoidal
A
B
C
B
A C
Figure 26 - Channel Types
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The minimum dimensions of an open channel shall be: A= 200, B= 200, C= 300. The minimum slope for an open channel is to be 1:200. The location of the open channel shall comply with the formation shoulder distance specified in ESC 410 “Earthworks and Formation”. Where track drainage is incorporated within existing track constraints (eg cuttings) and the shoulder distance cannot be achieved, open channels are to be an adequate distance from the track to prevent ballast spill into the channel area. In this case, the edge of the channel closest to the track shall be a minimum of 2800mm from the design track centre. This minimum edge distance shall be increased as required based on track configuration (rail size, sleeper type, ballast depth) and track curvature. The material forming the open channel shall to be capable of withstanding the maximum permissible design velocity. Table 4 in C4-5 nominates the maximum velocity values for varying lining types. If problems are encountered or an area is prone to erosion, then geotechnical advice should be sought. If fibre reinforced concrete is specified, synthetic fibres shall be used. With multiple tracks, drainage is to be provided by sumps and pipes in the ‘six-foot’ between each alternate track. All cess drainage systems must be designed to discharge to an approved watercourse or existing drainage system, and the approval of the appropriate authority must be obtained.
C4-2.2.2
Catch Drains Catch drains shall be provided on the uphill side of a cutting to divert water from the cutting face. Drains shall be 1000mm minimum from the face of the cutting.
Catch drains shall be provided on the uphill side of embankments to divert water from the embankment toe. Drains shall be 1000mm minimum from the toe of the embankment.
Catch drains may be either lined or unlined depending on the local soil conditions. Half round pipes or dish drains may be used instead of lined channels. The location of drains shall comply with the requirements of TMC 411 Earthworks Manual.
C4-2.2.3
Mitre Drains Where mitre drains are required, they shall be provided at regular centres with a drain located approximately every 100 metres maximum. They should be installed at the ends of cuttings. The minimum slope of mitre drains shall be 1 in 200. The ends of mitre drains shall be splayed to disperse water quickly and reduce scouring.
C4-2.3
Subsurface Drainage
C4-2.3.1
General Subsurface drains are used where adequate surface drainage cannot be provided due to some restriction or lack of available fall due to outlet restrictions. Subsurface drainage shall be provided in locations where the water table is at or near earthworks level. Subsurface drainage shall be provided along the cess, between, across, or under tracks as required.
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With double and multiple tracks, the requirement is that the water from one track shall not cross another track to get away. Drainage shall be provided by sumps and pipes in the ‘six-foot’ as required.
Advice should be sought from the Principal Geotechnical Engineer before designing and installing subsurface drainage.
Subsurface drainage systems shall be designed to take surface runoff, ground water and seepage, and water collected from other drainage systems to which the new system is being connected. Most systems will only have to cater for surface runoff. If a drainage system is required to remove ground water and seepage, a detailed hydrological and geotechnical investigation is required to determine the volume of water for the sizing of drains. The volume of water from other systems is determined from the outlet capacity of that system. Subsurface type drains generally consist of a combination of any one of the following:
C4-2.3.2
−
Pipes
−
Geotextile (or Geofabric)
−
Aggregate filter
−
Sumps, grates, and sump covers or cages.
−
Inlets and outlets
Pipes The capacity of the proposed drainage system shall be determined using the peak flow rate calculated by the Rational Method, with adjustment made for subsurface water and water collected from other systems. The peak flow velocity within the pipe shall be less than the manufacturer recommended maximum limits. Pipes larger than the design size may be adopted to reduce the likelihood of the system becoming blocked and also enable easier cleaning. The minimum pipe diameter shall be 225mm (for ease of maintenance cleaning). The slope of pipes shall be 1 in 100. Where this is not achievable, the pipe shall be laid at the maximum achievable slope. Slopes flatter than 1 in 200 require the approval of the Chief Engineer Civil. Depth of pipes under the track shall be 1600mm minimum from top of rail to top of pipe or pipe encasing. Depth of pipes running parallel to the track shall be 600mm minimum from the design cess level to top of pipe. At specific sites where it is not feasible to comply with these pipe depth requirements and achieve an effective drainage system design, the pipe depth may be reduced to: −
1200mm minimum from top of rail to top of pipe or pipe encasing for under track pipes;
−
300mm minimum from the design cess level or 1000mm from top of adjacent rail (whichever produces the lowest invert level) to top of pipe for pipes running parallel to the track.
Acceptable pipe materials are: −
reinforced concrete
−
fibre reinforced concrete
−
steel
−
products listed in Appendix 6.
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Approved proprietary products shall be designed and installed in accordance with the manufacturer’s specifications. Steel pipes shall be designed to mitigate the effects of electrolysis and stray track currents. Designs shall be in accordance with the requirements of RailCorp’s Chief Engineer Electrical Systems. Both slotted and unslotted pipes may be used depending on the system type and its means of collecting and carrying water. Slotted pipes are preferred, as these do not rely on surface flow between sumps to collect water. Slotted pipes and perforated pipes are not suitable for under track pipe work. Minimum strength requirements are detailed in Table 1. The strength of reinforced concrete and fibre reinforced concrete pipes shall be determined in accordance with AS 3725. Material
Type
Minimum strength class
Reinforced concrete
Slotted and unslotted
4
Fibre reinforced concrete
Slotted and unslotted
4
Steel
Slotted, perforated and unslotted
N/A
Table 1 Acceptable pipe types and minimum strength requirements
If railway live loads are applicable, then the pipes must be designed for train loads as follows:
Passenger Main Lines and Mixed Passenger Freight Main Lines
300-LA plus DLA
Light Passenger Main Lines
180-LA plus DLA
Heavy Freight Option
350-LA plus DLA
Sidings
300-LA plus 50% DLA Table 2 Railway Live Loads
NB. The ‘Reference Load’ is 300-LA. For the other loadings, all axles are to be proportioned by the ratio of the nominated LA load divided by 300. Operating Classes are defined in RailCorp standard ESC 200 “Track System”. For loadings less than 300 LA, future loading requirements need to be considered. Final approval of the design loads shall be obtained from the Chief Engineer, Civil. The Bridge Design Code, AS 5100.2, does not provide guidance on a suitable impact factor for railway loads distributed on fill. A dynamic load allowance (DLA) shall be adopted which varies linearly from 1.5 at 0.3m depth to 1.0 at 3.5m depth or greater (where the depth is measured from the top of rail).
Where slotted pipes are used, strength reductions for the slots shall be included in the design and shall be based on manufacturer’s recommendations.
Pipes located under sections of the rail corridor used for road vehicle access along the rail corridor, shall be designed for the R20 design load. See Appendix 7 for details of R loading configuration. Once the layout and required capacity of the drain has been established, it is necessary to detail the various items the will make up the system. This enables the correct components to be ordered quickly in the construction phase.
C4-2.3.3
Trench Excavation
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The width of trenches should only be as wide as necessary to ensure proper installation and compaction. The minimum trench width shall be pipe diameter plus 150mm on each side. For longitudinal drains located either within 2500mm of the track centre line or between tracks where track centres are less than 6000mm, the minimum trench width shall be pipe diameter plus 100mm on each side. Trenches shall be backfilled with suitable material and compacted to not less than 95% Relative Compaction as determined by AS.1289 Tests 5.1.1 and 5.3.1 (Standard Compaction).
C4-2.3.4
Pipe Bedding Type When determining the class of pipe to be specified in a sub-surface drainage system the bedding type assumed should be appropriate for what can be achieved during construction. Most under track drainage is constructed during track possessions where the more stringent requirements for placement and compaction of bedding material cannot always be achieved. For under track crossings that are to be constructed during a limited track possession, type “U” bedding in accordance with AS 3725 “Loads on buried concrete pipes” shall be used in design.
C4-2.3.5
Sumps, Ballast Cages and Covers Sumps are required as access points for surface water as well as for maintenance of the drainage system. Sumps shall be spaced at 30 to 50 metre centres, except through platforms where spacing shall be 20 to 30 metre centres. Reduced centres may be applicable in the 6-foot between tracks to account for track curvature. The minimum internal plan dimensions of a sump shall be 600mm x 600mm for depths greater than 1m. Minimum internal plan dimensions of 450mm x 450mm are acceptable for depths less than 1m.
Precast sumps with risers used to accommodate varying depths are to be adopted in preference to cast-in situ sumps.
All sumps are to be provided with a heavy-duty cast iron grate cover. In addition, all sumps within 2800mm of a track centre, or where site restraints dictate the possibility of ballast covering a pit, then a ballast cage (lobster pot) shall be provided. Refer to drawing CV 0400998 for details. Ballast cages shallbe of heavy-duty construction, capable of withstanding live loading from construction machinery. The cage shall be positioned to the outside edges of the sump. When installed the cages shall not extend above the top of sleeper level. Where the internal sump height (including risers) exceeds 1200mm, the following must be provided: −
Step rungs are to be provided at 300mm vertical centres. The step runs shall be located on the face looking at the oncoming train traffic (ie either Sydney face for the down track or Country face for up track).
−
Sump riser heights are to be selected such that step rungs do not come within 50mm of the top or bottom of the riser.
−
Where sumps are located in the 6-foot between tracks, the internal dimensions of the sump shall be increased to a minimum of 600mm wide (perpendicular to the tracks) x 900 mm to accommodate inspection access. The width shall be the maximum size available to enable proper placement of the sump and ballast cage (lobster pot) without clashing with the sleepers.
−
The internal dimensions of the sump in areas excluding the 6-foot, shall to be increased to a minimum of 900mm x 900mm to accommodate inspection access.
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Flushing Points Ground water and seepage drains shall have flushing points at appropriate intervals. Flushing points shall consist of “T” or “L” connections in the sub-surface pipe, with pipe connections extending to the surface for regular flushing with water to clear the sub-surface drain of fouling material.
C4-2.3.7
Aggregate Drains Aggregate drains are only suitable for use where small flow or seepage is expected. They are not to be used for the collection of surface water. The design of permeable drains may be carried out using Darcy’s equation. The permeability of clean gravel can range from 0.01 to 1.0 m/s. The aggregates used in aggregate drains are either 20mm nominal diameter or 53mm diameter (ballast), the permeability of these aggregates is: −
20 mm aggregate k = 0.15 m/s
−
53 mm aggregate k = 0.40 m/s
If in doubt as to the type of aggregate or the size of aggregate to use refer to RailCorp’s Geotechnical Engineer for advice. Aggregate drains are to be lined with a geotextile. A minimum 100mm layer of aggregate is to be placed on top of the geotextile to protect it from damage.
C4-2.3.8
Geotextiles The main purpose of a geotextile used in subsurface drainage is to act as a filter, which helps prevent silting-up of the drain it is protecting. The selected geotextile is to achieve the following characteristics: −
good permeability through the fabric material
−
good filtering qualities
−
resistance to clogging by particle fines
−
ability to stretch and conform to the shape of an open trench.
The selected geotextile is to exhibit the following mechanical properties as a minimum when tested in accordance with AS 3706: −
Tear Strength 400N
−
G Rating 2000
−
Grab Strength 1100N.
Geotextiles used in subsurface drainage must fully line the trench and have a minimum lap of 300mm at the top. The wrapped trench is to be covered by a minimum of 100mm of aggregate.
C4-2.3.9
Inlets and outlets There are various types of inlets and outlets in use. Some typical examples of inlets and outlets are: rip-rap, grouted rip-rap, sand bags, wire baskets (ie. gabions & reno matresses), revetment mattresses, precast concrete units and cast in place concrete. Example diagrams can be found in C3-3.4. To prevent soil erosion, all inlet/outlet points shall be provided with an appropriate size concrete headwall to suit the ground profile. Refer to drawings CV 0497068 and CV 0497069 for standard concrete headwalls.
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The ground covering at the pipe exit points shall be capable of withstanding the exit flow rates. Scour protection or energy dissipating devices may be required if existing ground cover cannot withstand the design rate. Where the sediment load of the water being discharged from a drainage system is high, a silt trap shall be included.
C4-3
Design Investigation
C4-3.1
Scope of investigation The main objective of a design investigation is to establish the requirements of the drainage system and any restrictions that may be imposed on the system. Aspects to be covered in the design investigation include: 1. Identification of the problem and thus the drainage objective. (i.e. what area is to be drained and for what reason). 2. Determination of the information required. (i.e. location, outside influences, fall available, possible outlets, access, site safety requirements, etc.) 3. Collection and study of all available existing/historical information. All available information from adjacent sites or the locality in general should be studied before embarking on any fieldwork. This will often save unnecessary fieldwork or may point out particular problems or aspects that should receive special attention. Included in this stage should be a full service search. This involves the check of the location of both RailCorp and public services. This may also involve site inspections with representatives from various bodies to accurately locate services, the position of which should then be marked, either on a plan or pegged. Other types of information that may be of use are, aerial photographs, maps (topographic, geological, soil, etc.), charts, meteorological and hydrological information). 4. Site inspection. A checklist should be prepared prior to the actual investigation so that the maximum amount of
information may be extracted from the site in a minimum time (see Form 1 in Appendix 3).
Items that should be looked at during a site inspection include:
∼
Access to and from the proposed site and any possible restrictions.
∼
Type and location of any existing drainage systems and any possible reasons for its
failure.
∼
The position and condition of any existing drainage outlets.
∼
Any other likely drainage outlets. Determine the outlet conditions and any likely restrictions because these may affect the design of the drainage system.
∼
Adjacent structures that may impact on the drainage design, or where the drainage design may cause instability to the structure.
5. Catchment area estimation: The catchment area for the drainage system needs to be estimated during the site inspection. This may be checked by comparison with maps of the area. A further inspection may be required at a later stage so that the area may be surveyed in order to establish the available fall and invert level for the inlet and outlet.
C4-3.2
Determination of the type of drainage system required On completion of the design investigation, information gathered shall be compiled and a decision made on the type of drainage system that is most suitable. The type of system chosen for each location is dependent on the site restraints, water source, track structure and long-term maintenance issues. The two types of drainage systems are surface and subsurface.
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If possible surface drains should be used in preference to subsurface drains since they are easily inspected and maintained. Note: care must be taken to ensure that the right drainage system is designed for each location. For example-using a slotted system to drain surface runoff that could have been collected by sumps. This could lead to a quicker failure of the system by allowing an easier route for water to pass (seep) into the formation.
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C4-4
Estimation of the Required Drainage System Capacity
C4-4.1
General At this point, the site requirements and restrictions, the drainage type, and the layout of the proposed drainage system should be known. The next step is to estimate the quantity of water that the drain will need to carry, so that the size of the drain and its various components may be determined. The quantity of water (QPF) that the drain is required to carry generally consists of: QPF = QR + QS + QC…………………………………………………………..(1) Where; QPF =
water quantity (m3/s or l/s)
QR =
runoff quantity collected (m3/s or l/s).
QS =
subsurface water quantity intercepted (m3/s or l/s)
QC =
collected water quantity from a drain of a connecting system (m3/s or l/s).
The calculated quantity (QPF) represents the peak flow that the drain will be required to carry, for a short time only. The quantity (QR) is calculated for the catchment size and critical rainfall duration by using the Rational Method. The value of intercepted subsurface water "QS" is difficult to determine. If a drainage system is required to remove intercepted subsurface water, a detailed hydrological/geotechnical investigation is usually required.
The volume of water conducted from other systems, "QC", is estimated from the outlet capacity of the system to which the new system is being connected. Provided the catchment area, drain size and slope are known (or can be measured), the maximum value of "QC" can be determined using the Rational Method. This information may also be available from the authority owning the asset (eg council). If the connecting system is a complex network of drainage a detailed study may be required. Account shall be taken of all water flowing onto the rail corridor from adjoining properties and streets.
C4-4.2
Average Recurrence Interval (ARI) In order to use the Rational Method it is necessary to adopt a relevant average recurrence interval (ARI). This is an approximate estimate of how often a particular event will occur on average. For example, an ARI of 1 in 50 years means that a particular storm event is likely to occur on average only once in every fifty years. If any modification to the ARI is desired, then a risk assessment shall be carried out to consider all impacts of such modification. Any modification to the ARI will need a waiver from RailCorp’s Chief Engineer Civil. Once the ARI is established the volume of water that the drain will carry can be calculated.
C4-4.3
The Rational Method The Rational Method provides a method for calculating the peak rate of discharge of a storm event for a specific ARI.
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If incorporating computer modelling in the design process, then a range of storm events representing varying rainfall duration shall be investigated. The drainage design shall be carried out adopting the critical rainfall event. Hydrology and hydraulic computer packages can be utilised for the design of track drainage. The following procedure deals with hand calculation methods only. The Rational Method is detailed fully in Australian Rainfall and Runoff (AR&R) published by the Institution of Engineers, Australia. The AR&R publication recommends the following steps for flow rate determination for sites in eastern New South Wales. Form 2 in Appendix 4 breaks down these steps and can be used as a calculation sheet. 1. Calculate the critical rainfall duration (tC) for the area under investigation Two methods may be adopted to calculate the critical rainfall duration. These methods are: i. ii.
Equal area stream slope’ – recommended for hilly or undulating sites as it gives a more realistic flow response time (refer to AR&R for this procedure). Basic formulae (for Eastern New South Wales) tC=0.76 A
0.38
…………………………………….…………………..(2) Where; tC = critical rainfall duration (in hours) A = catchment area (km2)
The catchment areas required for peak flow rate calculations shall be determined using (in order of preference) site survey, site measurements or suitably scaled topographic maps. 2. Calculate the critical 50 year design rainfall intensity (Icr,50). This step comprises of looking up a series of basic rainfall intensities, skewness factors and geographical factors from contour style maps found in Volume 2 of the AR&R guide. These values can be plotted on a log-Pearson Type III diagram (LPIII) or incorporated in interpolation formulas found in Book 2 of AR&R volume 1. From either of these two methods the 50 year design rainfall intensity ‘Icr,50’ for the critical duration tC can be determined. 3. Determine the 50 year runoff coefficient (C50) for the geographical area by determining the following: iii. Read the 10 year runoff coefficient value (C10) from Figure 1.1 in Volume 2 of the AR&R iv. Geographical zone B is adopted from Figure 1.2 (AR&R) – for Sydney Metropolitan Area. v. Interpolate or calculate the 50-year frequency factor FF50 from Table 1.1 (AR&R) based on site elevation. vi.
Calculate C50 = C10xFF50 (no units)
4. Calculate the 50 year peak flow rate (Q50). Adopt the Rational Method formula. Q50 = F×C50×Icr,50×A………………………………….…………………..(3) Where; Q50 =
peak flow rate (m3/s) for ARI =50 years
F=
conversion factor to balance units used. = 0.278 if A is in km2 = 0.000278 if A is in hectares (ha).
C50 =
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I cr,50=
average rainfall intensity (mm/hr) for the critical duration
A=
catchment area (km2 or ha).
The peak flow rate is utilised in determining how much water is likely to rain onto a catchment and thus enabling the sizing of the drainage system under consideration.
C4-5
Surface Drain Design The following steps can be used to correctly determine the required size of surface drainage: Step A: Determine the required channel capacity Prior to estimating the size of a surface drain the required capacity must either be known or calculated using Equation 1. QPF = QR + QS + QC…………………………………………………………..(1) For surface drains " QS " and " QC " can usually be neglected. In this case, Equation 1 becomes QPF = QR = Peak flow rate (m3/s). Example 1: A rainfall runoff quantity of 0.15m3/s was calculated to act on a catchment for the 50-year ARI critical duration storm (from the “Rational method”). There is no subsurface water intercepted, but a nearby stormwater pipeline enters the channel and adds 0.07 m3/s. What is the total water quantity the channel will need to be designed for? Solution 1: The design flow capacity can be determined from Equation (1)
QPF = QR + QS + QC = 0.15 + 0 + 0.07 = 0.22 m3/s
The channel will need to be sized to take a 0.22m3/s flow rate or greater.
Step B: Select a Mannings roughness coefficient A value of the roughness coefficient 'n" must then be selected from Table 3. Channel Material
Roughness Coefficient ‘n’
Closed Conduits concrete pipe or box
0.012
corrugated steel pipe - helical
0.020
vitrified clay pipe
0.012
fibre cement pipe
0.010
P.V.C. pipe
0.009
steel pipe
0.009 - 0.011
Lined open channels concrete lining
0.013 - 0.017
gravel bottom concrete sides
0.017 - 0.020
gravel bottom rip rap sides
0.023 - 0.033
asphalt rough
0.016
asphalt smooth
0.013
Unlined channels - Earth uniform section
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clean channel
0.016 - 0.018
with short grass
0.022 - 0.027
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Channel Material gravelly soil
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Channel Material
Roughness Coefficient ‘n’
Unlined channels - Earth fairly uniform section no vegetation
0.022 - 0.025
grass plus some weeds
0.030 - 0.035
dense weeds
0.030 - 0.035
clean sides gravel bottom
0.025 - 0.030
clean sides cobble bottom
0.030 - 0.040
Rock smooth and uniform
0.035 - 0.040
jagged and irregular
0.040 - 0.045
Table 3: Value for Manning's roughness co-efficient "n" for different pipe & channel types. Step C: Determine the slope of the drain The minimum slope of a drain is 1 in 200 (i.e. 1 metre fall vertically for every 200 metres horizontally), though a minimum slope of 1 in 100 is preferred for self-cleaning purposes. It should be noted that as the slope of the drain becomes flatter, the tendency for a drain to become blocked due to sediment build-up increases. Consequently the maintenance of the drain also increases. Step D: Select a trial channel size Using the value of slope "S" and the roughness coefficient "n" selected previously, the capacity of the trial drain can be calculated using Equation 4 (Manning's equation) or a simplified version (Equation 5).
Q=
1 × A × R0.67 × S0.5 n ………………………………………..………(4)
Where; Q=
flow rate or capacity (m3/s)
n=
roughness co-efficient. From Table 3
A=
channel cross-sectional area
R=
hydraulic radius - examples given in Table 4
R=
A/P where P = wetted perimeter (i.e. the surface in contact with the water)
S=
slope of the drain.
If X = A x R0.67 Equation 4 becomes:
Q=
1 × X × S0.5 n ………………………………………….. (5)
See Table 4 for values of "X" for various channels:
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Channel Types: Type 1 - Trapezoidal
Type 2 - Rectangular
A B
C
B
Channel Dimensions (mm) No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
A 200 200 200 200 200 300 300 300 450 300 300 300 300 300 450 300 300 300 450 300 450 450 450 300 450 450 450 600 600
A
B 200 300 200 200 300 200 450 300 200 450 300 450 200 300 300 450 300 450 450 300 450 600 600
C 300 450 300 300 450 450 300 300 450 450 300 450 600 450 600 600 600 900 450 900 900 450 600 900 600 900 900 600 900
C Area (m2)
Wetted perimeter (m)
Hydraulic radius (m)
“X” (Eqn 5)
0.060 0.090 0.100 0.120 0.130 0.135 0.150 0.180 0.203 0.195 0.225 0.225 0.240 0.270 0.270 0.270 0.315 0.330 0.338 0.360 0.405 0.405 0.405 0.405 0.473 0.540 0.608 0.720 0.900
0.700 0.850 0.860 1.021 1.016 1.050 1.021 1.149 1.350 1.171 1.382 1.299 1.321 1.532 1.500 1.449 1.682 1.621 1.532 1.749 1.800 1.723 1.682 1.441 1.873 1.982 2.173 2.297 2.597
0.086 0.106 0.115 0.118 0.128 0.129 0.147 0.157 0.150 0.167 0.163 0.173 0.182 0.176 0.180 0.186 0.187 0.204 0.220 0.206 0.225 0.235 0.241 0.281 0.252 0.272 0.280 0.313 0.347
0.012 0.020 0.024 0.029 0.033 0.034 0.042 0.052 0.057 0.059 0.067 0.070 0.077 0.085 0.086 0.088 0.103 0.114 0.123 0.125 0.150 0.154 0.157 0.174 0.188 0.227 0.260 0.332 0.440
Table 4: Calculation of “X” for various channel sizes. Note: Smaller channels tend to become blocked with built up sediment very quickly.
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The following are typical examples of calculations to determine the capacity of an open channel. Example 2: For a trapezoidal channel (shown below) with a slope of 1 in 200 and a roughness coefficient "n" of 0.030. Calculate the channel capacity using a) equation 4 and b) equation 5 and Table 4:
300 450
600
450
Solution 2a) - using Equation 4 S = 1 in 200 = 0.005 n = 0.030 A = (600 × 300) + 2 × (0.5 × 300 × 450) A = 315,000 mm2 A = 0.315 m2 R = A/P
P = 2 × (300) × 2 + (450) × 2 + 600 P = 1682 mm
P = 1.682 m
R = 0.315/1.682
R = 0.187 m
Q=
1 × A × R0.67 × S0.5 n
Q=
1
× 0.315 × (0.187)0.67 × (0.005)0.5 0.03
Q = 0.243 (m3/s)
Solution 2b) - using Equation 5 and Table 4. S = 0. 005
n = 0.030
From Table 4, X = 0.103
Equation 4
Q=
1
× X × S0.5 n
Q=
1 × (0.103) × (0.005)0.5 0.03
Q = 0.243 (m3/s)
Step E: Check channel capacities Once the capacity of the trial drain is determined “Q” it must be compared with the required capacity found using Equation 1 “QPF”. If the capacity of the trial drain “QPF” is considerably greater or lesser than the required capacity “Q”, then a new trial drain should be selected and steps (c) and (d) repeated until the trial capacity is approximately equal to or slightly greater than the required capacity.
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Example 3: Check that the channel in Example 2 has is sufficient capacity to cater for the design storm as calculated in Example 1. Solution 3: The channel capacity “Q” of 0.243m3/s (Example 2) is greater than the design storm flow rate “QPF”of 0.220m3/s (Example 1). Therefore it has sufficient capacity. Step F: Calculate water velocities Once the required capacity is obtained, the flow velocity of water within the channel may be calculated. The velocity is calculated using Equation 6 as shown below: V=Q/A………………………………………………………………..(6) Where: V=
velocity (m/s)
Q=
flow rate (m3/s) calculated using Equation 1
A=
area of selected channel (m2)
Example 4: Calculate the flow velocity of water within the channel in Example 2. Solution 4: Q=0.22m3/s
A=0.315 m2 (from example 1-assumed flowing full)
V = Q/A = 0.220/0.315 = 0.69 m/s
Step G: Check channel lining In some cases it may only be possible to install a small drain and the flow through this drain may have a velocity greater than the maximum permissible velocity and consequently the channel must be lined. Table 5 gives the maximum permissible velocity of varying ground coverings. Channel Type Fine sand Silt loam Fine gravel Stiff clay Coarse gravel Shale, hardpan Grass Covered Stones Asphalt Boulders Concrete
Velocity (m/s) 0.45 0.60 0.75 0.90 1.20 1.50 1.8 2.5 3.0 5.0 6.0
Table 5: Maximum permissible velocities for various types of channel lining. Lining a channel changes the roughness coefficient "n"', and thus the capacity of the channel may be altered either up or down (See Table 3). A lining is selected such that the allowable velocity for the type of lining is greater than that calculated in step F, this is used as a first trial value.
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Example 5: The channel in example 4 is lined with grass covering. Is it sufficient to withstand the flow velocity. Solution 5: Velocity of water in channel = 0.69m/s (solution 4)
The maximum permissible velocity of grass lining = 1.8m/s (Table 5).
Therefore, grass has the required resistance and the lining is sufficient.
Step H: Completion If the capacity of the channel is inadequate or the ground cover velocity insufficient then modifying the channel size, slope or lining type will need to be done until all aspects are satisfactory. Complete Example
Example 6:
Calculate the required Channel size and lining type given that the required capacity of the 3 channel is 0.40 m /s. The existing soil is clay. Solution 6: Trial 1:
Step A: No subsurface water or connecting system. So QPF =0.40m3/s
Step B: n=0.016 (Table 3)
Step C: Adopt S=0.01 (desirable minimum slope)
Step D: Select Channel No. 14 from Table 4. A = 0.270 m2. X = 0.085
Q=
1 × X × S0.5 n = (1/0.016)x(0.085)x(0.01)0.5 = 0.53m3/s (Eq’n 5)
Step E: Channel capacity 0.53 m3/s> design capacity 0.40m3/s. ok Step F: V = Q/A = 0.40/0.270= 1.48m/s (Equation 6) Step G: Clay has permissible velocity capacity of 0.9m/s (Table 5) which is less than the design flow of 1.48m/s. Could modify size or change lining. Opt for a change of lining type to grass covered (capacity 1.8m/s). Step H: Must redo calculations, as n will change Trial 2: Try lining with higher permissible velocity – say grass lining Steps A, B & C: QPF =0.40m3/s. n=0.024 (Table 4). S=0.01 Step D: Same Channel No. 14 from Table 4. A = 0.270 m2. X = 0.085 Q= (1/0.024)x(0.085)x(0.01)0.5 = 0.35m3/s (Equation 5) <0.4m3/s therefore no good. Could modify size or change lining. Trial 3: Try smoother lining, with high permissible velocity - say asphalt Steps A, B & C: QPF =0.40m3/s. n=0.013 (Table 4). S=0.01 Step D: Same Channel No. 14 from Table 4. A = 0.270 m2. X = 0.085 Q= (1/0.013)x(0.085)x(0.01)0.5 = 0.65m3/s (Equation 5) Step E: Channel capacity 0.65 m3/s> design capacity 0.40m3/s. ok Step F: V = Q/A = 0.40/0.270= 1.48m/s (Equation 6)
Step G: Asphalt has capacity of 3.0m/s (Table 5) which is greater than the design flow of
1.48m/s. Therefore it is satisfactory.
Step H: Channel No 14 laid in bitumen at a 1% slope is satisfactory.
C4-6
Subsurface Drain Design
C4-6.1
Pipe Drains
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The following steps can be used to correctly determine the required size of subsurface drainage pipes: Step A: Determine the required pipe capacity Prior to estimating the size of a subsurface drain the required capacity must either be known or
calculated using Equation 1.
QPF = QR + QS + QC …………………………………………………………..(1)
Refer to Section 4.5 for more detail.
Step B: Select the pipe type The pipe type selected should be adopted based on the suitability of the system to the site. Unslotted pipes must be used for undertrack pipes whereas either slotted or unslotted pipes can be used elsewhere. Acceptable pipe materials by type are detailed in Table 1. Step C: Adopt a Mannings roughness coefficient A value for pipe roughness “n” can be obtained from the manufacturer for the product being adopted. Table 3 details typical values that are also acceptable. Step D: Determine the slope of the pipe The pipe slope may be determined from the geometry of the site to best suit site constraints. However, the minimum pipe slope is 1 in 300, (although a slope of 1 in 100 is preferable for selfcleaning purposes). The steeper the slope the lesser the maintenance requirements). Step E: Select a pipe size A trial pipe size can be found using Table 6 by selecting a pipe where “Q” is greater than the peak flow required “QPF”. Alternatively, The capacity of the pipe can be found by using Mannings Equation (Equation 4). Pipe Dia.
Pipe Material
225
F.C.
1 in 100 200
Max Flow Q (l/s) 58.3 41.2
225
Concrete
1 in 100 200
300
F.C.
300
450
F.C.
1 in 100 200
Max Flow Q (l/s) 370.3 261.8
53. 0 37.4
450
Steel
1 in 100 200
264.5 187.0
1 in 100 200
125.6 88.8
450
Concrete
1 in 100 200
336.6 238.0
Steel
1 in 100 200
104.6 74.0
525
F.C
1 in 100 200
558.7 395.0
300
Concrete
1 in 100 200
114.1 80.7
525
Concrete
1 in 100 200
507.9 359.1
375
F.C.
1 in 100 200
227.7 161.0
600
F.C.
1 in 100 200
797.7 564.0
375
Steel
1 in 100 200
175.1 123.8
600
Steel
1 in 100 200
498.5 352.5
375
Concrete
1 in 100 200
207.0 146.6
600
Concrete
1 in 100 200
725.1 512.7
Drain Slope
Pipe Dia.
Pipe Material
Drain Slope
Table 6 Capacities for various pipe types and sizes. L Notes to Table 6 1. FC = fibre cement pipe
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Steel = corrugated steel pipe Concrete = concrete or vitrified clay pipe PVC pipes are not to be used for track drainage design. They are included in Table 6 for assessment of existing pipe systems. To convert m3/s to l/s multiply by 1000 (ie 1000 litres = 1 cubic metre) The values of Mannings' roughness co-efficient used in the calculations for the values given in table 5 are as follows:
5. 6.
Concrete
n = 0.011
Fibre Cement
n = 0.010
P.V.C.
n = 0.009
Steel
100 - 300 dia
n = 0.012
375 dia
n = 0.013
450 dia
n = 0.014
600 dia
n= 0.015
Step F: Check the flow rates within the pipe Utilising Equation 5 (V=Q/A), the velocity of flow within the pipe can be determined. The flow velocity within the pipe shall be at an acceptable level so as not to cause damage to the pipe surface. The manufacturer has recommended maximum limits. Step G: Determine the strength of the pipe (pipe class) The pipe must be checked to see if it is suitable for the design and construction loads that are imposed on it. The method of calculation of pipe strength is to follow the relevant Australian Standard (eg AS 3725 – Loads on buried concrete pipes). If pipes are within a 45-degree projection of the outside of the sleeper (in any direction), then railway loading must be included. Dynamic loads must also be applied – Refer to section 4-2.3. If pipes are situated within a 45-degree projection of the outside of an access road (in any direction) then the loads applicable to the access vehicle must be included. Dynamic loads must also be applied – Refer to section 4-2.3. Pipe strength is also highly dependent on the type of trench excavation, fill material and compaction technique. When determining the class of pipe to be specified in a drainage system, type “U” bedding should be assumed, even if better bedding is specified on the drawings. Most track drainage is constructed during track possessions where the specified placement and compaction of bedding material cannot always be achieved. Where slotted pipes are used, strength reductions for the slots shall be included in the design and shall be based on manufacturer’s recommendations. Manufacturer supplied computer software is acceptable for this purpose of pipe strength design, provided it is in accordance with AS 3725. Minimum strength requirements are detailed in Table 1. Complete Example: Example 7: 3 A rainfall runoff quantity of 0.10m /s was calculated to act on a catchment for the 50-year ARI critical duration storm (from the rational method). There is no subsurface water intercepted, but a nearby stormwater pipeline enters the system and adds 0.02m3/s. What size reinforced concrete pipe is required to satisfy flow requirements?
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QPF = QR + QS + QC = 0.10 + 0 + 0.02 = 0.12 m3/s Step B: Reinforced concrete (given) Step C: Roughness n=0.011 (from Table 6 – notes) Step D: Pipe slope 1 in 200 (given) Step E: From table 6, a 375mm diameter RC pipe has capacity of 146.6l/s (0.146m3/s) which is greater than the design flow capacity. Also, the size is greater than the 225mm minimum. Step F: Flow rate within the pipe V=Q/A = 0.12/(3.142x0.375x0.375/4) = 1.1m/s which is less than the acceptable limit for concrete (6m/s). Therefore ok.
C4-6.2
Aggregate drains Aggregate drains are only suitable for use where small flow or seepage is expected. If a larger flow is expected a slotted pipe should be added to the system, and then the drain should be sized as described previously. A typical example of an aggregate drain is a blanket drain. Another type of aggregate drain is a French drain. Aggregate drains are to be lined with a geotextile. The capacity of an aggregate drain may be determined using Darcy's equation (Equation 7). Q = k × i × A ……………………………………………..……………….(7) Where: 3 Q = flow (m /s)
k = permeability of the aggregate i = hydraulic gradient or slope. A = cross sectional area (m2) The permeability of clean gravel can range from 0.01 to 1.0 m/s. The aggregates used in aggregate
drains are either 20 mm nominal diameter or 53 mm diameter (ballast), the permeability of these
aggregates is:
20 mm aggregate k = 0.15 m/s
53 mm aggregate k = 0.40 m/s
Equation 7 may be simplified if K = k × i, and Equation 8 becomes:
Q = K × A …………………………………………………………………(8)
Table 7 below gives values for "K" for use in Equation 8 in order to determine the capacity of
aggregate drains:
Slope
K = k × i (m/s) 20 mm
53 mm
1 in 100
0.00150
0.0040
1 in 200
0.00075
0.0020
1 in 300
0.00050
0.0013
1 in 400
0.00038
0.0010
1 in 500
0.00030
0.0008
Table 7 Values of K = k.i for various slopes.
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Example 8: If Q = 0.01 m3/s or 10 l/s an aggregate drain using 20 mm aggregate at a slope of 1 in 200, what size drain is required? Solution 8: Q=K × A this may be rearranged to: A = Q/K Therefore: A = 0.01/ 0.00075 A = 13.3 m2 For the same flow using 53 mm aggregate at a slope of 1 in 200, the area required is: A = 0.01 / 0.002 A = 5.0 m2
C4-7
Other Design Considerations When selecting a pipe, the type of environment must also be considered (i.e. is the water abrasive, acidic or alkaline). The manufacturer’s specifications should be consulted regarding the pipe’s suitability to various environments. Sizing of surface and subsurface drainage should consider maintenance implications. Using oversized channels may reduce sediment build-up and reduce maintenance. Adopting larger pipes may be beneficial fro access and cleaning requirements. The possible effects of non standard ballast profiles shall be considered. Geometry effects of laying longitudinal pipes adjacent track around curves shall be considered (eg may require reduced sump centres). The permanent effects of the drainage system located alongside existing structures (eg OHWS, retaining walls, platforms, embankments etc) shall be taken into account. The possibility of causing instability of an existing structure during the excavation stage must also be highlighted and accounted for. Conflict with existing services shall be included. Service searches shall be conducted and the locations of these services indicated on the design documentation.
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Chapter 5 Construction of Track Drainage This section deals briefly with the various forms of drainage construction. One important consideration is that each and every site must be assessed on its own merits. No two sites are ever exactly the same. This must be taken into account when selecting the site protection, equipment, and personnel required for each particular site. This section discusses the various steps involved in the construction of both surface and subsurface drainage systems.
C5-1
Line and Grade The line and grade of the drainage system, be it surface or subsurface, may be set out by one or a combination of the following methods: 1. Stakes, spikes, shiners (small reflective metal discs), marks or crosses set at the surface on an offset from the desired centre line. 2. Stakes set in the trench bottom on the pipeline as the rough grade for the pipe is completed. 3. Elevations given for the finished trench grade and pipe invert while laying the pipe or excavating the trench is in progress. Of these three methods, method (1) is the most commonly used for track drainage. Method (1) involves stakes, spikes, shiners, or crosses being set on the opposite side of the trench from where the excavated material is to be cast at a uniform offset, in so far as practicable, from the drain’s centreline. A table known as a cut sheet is prepared. This is a tabulation of the reference points giving the offset and vertical distance from the reference point to either: the trench bottom, the pipe invert or both. When laying the pipe it may be more practical to give two vertical distances, one to the trench bottom (excavation depth) and one to the top of the pipe, which is generally easier to measure to than the pipe invert. The grade and line may be transferred to the bottom of the trench by using batter boards, a tape and level, or patented bar tape and plumb bob unit. This method may be adapted to suit. For example it is common practice to have the proposed route surveyed with the reference points marked on the datum rail (either the Down rail or the low rail on a curve). The offset and vertical height may be easily transferred from the rail by use of a straight edge, spirit level and tape (see Figure 27 below).
Spirit level Straight edge
Measure depth from underside of straight edge to bottom of trench
Ballast
Sub soil
Trench
Figure 27 - Method of measuring the depth of a trench and offset to pipe centreline. If the track is on a constant grade that is suitable for the pipeline and trench, this grade may be adopted. This gives a constant vertical depth from the datum rail to the trench bottom and pipeline, making construction and grade control much easier. © Rail Corporation Issued December 2009
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Another method of controlling the line and grade is the use of lasers. A laser beam is passed through the centre of the pipeline at the desired grade. It strikes opaque targets attached to the end of the pipe, and the pipe may then be either lifted/packed or lowered until the laser passes through the centre of the target.
C5-2
Site Preparation The amount of preparation varies from site to site. Operations that should be classified as site
preparation are:
−
clearing;
−
removal of unsuitable soils;
−
preparation of access roads;
−
detours and bypasses;
−
improvements to and modification of existing drainage;
−
location, and protection or relocation of existing utilities.
The success of the construction phase depends to a great degree on the thoroughness of the
planning and the execution of the site preparation work.
C5-3
Excavation With favourable ground conditions, excavation can be accomplished in one simple operation. Under more adverse conditions it may require several steps, such as; clearing, rock breaking, ripping or blasting and excavation. When excavating for a pipeline the trench at and below the top of the pipe should be wide enough to ensure adequate compaction on the sides of the pipe can be achieved. The minimum width on either side of the pipe shall be in accordance with C4.2.3.3. The amount of excavation and the types of equipment required may vary, so each site must be assessed on its merits to determine the type and quantity of equipment necessary. Excavation in the vicinity of structures shall comply with the requirements of TMC 411 Earthworks Manual. Particular conditions that should be taken into account when selecting equipment are: −
Site access
−
Size and amount of excavation necessary
−
Site conditions i.e. firm or boggy ground conditions
−
Location and availability of plant
−
Whether the plant item required has to be floated to the site. (If so the offloading conditions and a suitable area should be checked).
−
Services in the area.
Typical items of plant (equipment) utilised are:
−
Gradall (normal or highrail)
−
Backhoe
−
Tiltable dozers
−
Graders
−
Front end loaders
−
Tracked excavators
−
Hydraulic excavators
−
Bogie tippers and 4wd dumpers, etc.
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C5-4
Surface Drain Construction
C5-4.1
Requirements The main purpose of surface drains is to remove surface water from near the tracks and disperse it as quickly as possible. To do this, the drainage trench or ditch should be constructed at a uniform even grade, with no low sections where water may pond and seep into track formation, thus defeating the purpose of the drainage system. The grade of the drainage trench should be a minimum of 1 in 200 where practicable. Flatter grades may be used but require more regular inspection and maintenance, since they tend to become blocked with sediment more quickly than drains with steeper grades. Where the velocity of the water is greater than that shown in Table 5 in C4-5, some form of scour protection is required eg. lining the channel. Where doubts exist as to the erodability of a soil, RailCorp’s Geotechnical Engineer should be consulted. Where any surfaces are cleared of vegetation, these areas must be re-vegetated at the end of construction, to prevent unnecessary build-up of silt in nearby drains.
C5-4.2
Construction Steps −
Survey the proposed drainage route. This may be carried out during the preliminary investigation.
−
Establish and mark out reference points for use during construction. Marking out may consist of paint marks on the datum rail or star pickets. The interval used for the reference marks depends on the length of the drainage system. For example, for a short drain the interval may be 5.0 metres.
−
Clear the site. This should be part of any site preparation work carried out. This may involve relocation of signal troughing, clearing vegetation, etc.
−
Excavate to required level. When excavating the trench, use a bucket width equal to the width of the trench base, then add a batter to the sides of the trench formed. Monitor excavation with the method described in Section 5.1. Once the trench has been constructed, level and compact the trench base making sure that no low points exist.
−
Check for risk of erosion. If this is expected to be high the drain may require lining.
−
Clean up the site and revegetate any denuded slopes.
Note: It is good practice to work from the lowest to the highest point. That way if work is interrupted for any reason at least part of the drainage system will function correctly in the event of any rainfall occurring before completion.
C5-5
Subsurface Drain Construction The following sections detail construction methods for the following subsurface drains:
C5-5.1
−
Longitudinal drains
−
Lateral drains
−
Blanket drains
−
Horizontal and vertical drains
−
Pipe drain using unslotted pipes
−
Sump installation
Longitudinal Drain Construction This is the most commonly used form of subsurface drain used for track drainage. The basic construction steps are as follows: −
Survey the site.
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−
Establish the reference points. These may be paint marks on the rails or star pickets. The purpose of these marks is to provide points from which the depth of the trench and pipe invert level may be measured accurately. (See Section 5.1).
−
Excavate to the desired level. The type of equipment used to excavate the trench differs from location to location, depending on such parameters as; access, material, volume to be excavated and clearances for the safe operation of equipment.
−
The depth of the excavation depends on the pipe location, and outlet and inlet requirements. For pipes running parallel to the track, the minimum pipe cover is to be 600mm below the design cess level. Where this is not feasible, the minimum pipe cover is to be 300mm below the design cess level or 1000 mm below the adjacent rail level (whichever produces the lowest invert level). Note: the design track formation profile shall be as set out in TMC 411. The width of trenches should only be as wide as necessary to ensure proper installation and side compaction. The minimum width shall be pipe diameter plus 150mm on each side. For longitudinal drains located either within 2500mm of the track centre line or between tracks where track centres are less than 6000mm, the minimum trench width shall be pipe diameter plus 100mm on each side. 150/100 Pipe dia
150/100
Figure 28 - Trench width Installing drainage system. The method of installing this type of subsoil drain depends on the type of subsoil and other conditions encountered. (a). Impervious soil - aggregate filled excavation (that is, most clays are relatively impervious). Refer also to Figure 15. i.
Lay the geotextile in the bottom of the trench. Where joints need to be made in the geotextile a minimum overlap of 1 metre should be made.
ii.
Place a layer of aggregate in the bottom of the trench approximately 50mm thick. The aggregate used for this should be 20mm nominal diameter aggregate.
iii.
Lay the pipe sections, one section at a time on top of the aggregate.
iv.
Place pits/sumps and remove knockouts
v.
Check and adjust the pipe level and grade if necessary by packing aggregate under the pipe.
vi.
Place aggregate around and over the pipe, tamping the aggregate on the sides of the pipe as the trench is filled. Once the pipe is covered, complete the filling of the trench compacting the aggregate in layers no greater than 150 mm thick, using a vibrating plate compactor or similar.
vii. Fold geotextile over the top of the trench, ensuring that the ends are overlapped a minimum of 300mm. viii. Place a minimum 100mm thick layer of aggregate over the geotextile and grade the surface ix.
Pack knockouts from the inside of the pits using sand/cement mortar (or geotextile if detailed in this manner)
x.
Complete associated works (eg pit lids/pots, ballasting etc).
(b). Pervious soil – aggregate filled excavation (for example sandy soils). Refer also to Figure 16. When laying a drain in pervious soil it is necessary to place an impervious layer in the base of the trench. Typical impervious layers are concrete, cement or lime stabilised fill or clayey fill. © Rail Corporation Issued December 2009
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The impervious layer is to be 100mm thick at the edges of the trench and slope towards the centre of the trench where it is to be 50mm thick. Once an impervious layer is installed, the remaining construction steps are the same as steps "i" to "x" for drains in impervious soils above. (c). Geotextile wrapped pipes Sometimes it is beneficial to wrap the pipe inside a geotextile rather than around the outside of a trench. In this case repeat the procedure of (a) with the exception of: (i) the geotextile is wrapped and lapped a minimum 300mm around the pipe and (vii) is not required. (d). Earth Filled excavations - unslotted pipes i.
Place bedding sand/roadbase in the trench and compact as per the design
ii. Lay the pipe sections, one section at a time on top of the bedding. iii. Check and adjust the pipe level and grade if necessary. Adjust pipes by removal of base material or ramming additional bedding under the pipe. Alternatively, slings may be used around pipe ends. iv. Place pits/sumps and remove knockouts v. Place side zone material and compact to the required relative density as shown on the drawing. vi. Place a 150mm maximum layer of material over the pipe and use a vibrating plate compactor or similar to compact the fill to the required relative density. Repeat backfilling and compaction until fill is at final level vii. Pack knockouts from the inside of the pits using sand/cement mortar (or geotextile if detailed in this manner) viii. Complete associated works (eg pit lids/pots, ballasting etc). (e). Limited length due to outlet restrictions. In some locations a subsoil drain cannot be located deep enough to prevent it being disturbed by track maintenance machines. In this case the pipe may be wrapped in geotextile, then placed in the trench on a bed of aggregate to allow any adjustments to the level and grade of the pipe to be made, the trench may then be filled with a suitable pervious fill and compacted in layers. (f). Ash Pockets Where isolated pockets of ash are encountered, an impervious membrane may be placed in the trench before the fabric is laid. This membrane should cover the ash pocket and extend approximately 2 metres either side of it. The rest of the drain is constructed as set out in (a) above. This method is used only where the soil on either side of the ash pocket is impervious, otherwise the drain is constructed as per (b) above. If an impervious membrane is not available the section of the drain above the ash pocket may be constructed as for a drain in a pervious soil. See Figure 29 for the treatment of ash pockets.
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Geotextile
Impermeable membrane
Soft material (eg ash)
Impermeable membrane Subsoil drain
Ash pocket
2m
2m
Figure 29 - Construction of a drain over an ash pocket.
C5-5.2
Lateral Subsurface Drain Construction This type of drain is commonly used to drain under turnouts and isolated water pockets in embankments. For turnouts the construction of lateral drains is the same as that for longitudinal drains, the main difference is the depth of the pipe below rail level which is a minimum of 1200 mm. For embankment drainage, a lateral trench is excavated to the desired level, using a backhoe or similar. Once the trench is excavated to the desired level, the base is graded to fall away from the embankment centre. The construction methods are the same as for longitudinal drains (point (d) above).
C5-5.3
Blanket Drain Construction This type of drain is most commonly found at the base of embankments. Blanket drains are usually constructed during embankment construction, embankment widening or repairs to a slip. The construction steps are as follows:
C5-5.4
−
Excavate. For embankment widening or slip repair, steps should be cut into the existing embankment (see RailCorp Manual TMC 411)
−
Level and compact the base with a fall away from the embankment centre.
−
Lay out the geotextile. Any joints should have a minimum 1 metre overlap.
−
Place aggregate, usually 20 - 53 mm aggregate up to 300mm thick. (This should be laid and compacted in layers).
−
Fold sides of geotextile up over the top of the aggregate, then cover with a layer of Geofabric over the top of the aggregate.
−
Place riprap (100 - 150 mm stone) over the exposed face of the drainage blanket as protection.
−
Build up the embankment to the desired level and compact in layers.
Other Types Included in this section is the construction of horizontal and vertical drains. These drains are not often used for track drainage and consequently will not be dealt with at this stage, with the exception of the following. The most commonly used vertical drain is used to drain water from behind retaining walls and bridge abutments. This drain consists of a geotextile layer placed at the back of the wall and connected to a pipe at the base of the wall.
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Water reaching the geotextile can flow along the plain of the fabric that is down the back of the wall, and is then removed by the pipe at the base. This may also be combined with horizontal layers of geotextile to collect water seeping through the embankment or backfill behind the wall, which is conducted towards the vertical drain and then to the carrier pipe and removed. This type of drain may be placed during construction and backfilling, or an area behind the wall can be excavated for their installation.
C5-5.5
Construction of an Unslotted Pipe Drain Follow the procedure as per (d) above.
C5-5.6
Sump Installation Sumps shall be spaced at 30 to 50 metre centres, except through platforms where spacing shall be 20 to 30 metre centres. Reduced centres may be applicable in the 6-foot between tracks to account for track curvature. At the location at which a sump is to be placed the trench is widened and deepened to accommodate for the sump. The base of the trench is then levelled and covered with a layer of compacted sand or road base, which is a minimum 150mm deep. This layer may be added to so that the sump is positioned at the correct height. Prior to placing the sump the wafer of concrete covering the inlet and outlet is knocked out to approximately the desired size. Drains using slotted pipes and geotextile are connected to sumps as shown in Figure 30 below. Once the pipe is in place any remaining gaps between the pipe and the sump are grouted. The trench is then filled and compacted. Sump cage Grate Sump
Geotextile Aggregate
Slotted pipe
Fabric is wrapped and twisted to hold back stone
Fiqure 30 - Method of joining longitudinal subsoil drain to sumps.
C5-6
Other Types of Construction Other construction methods that may be used are: −
Pipe jacking
−
Tunnelling
−
Augering
−
Cast in place
These are seldom used for track drainage, and therefore will not be dealt with.
C5-7
Inlets and Outlets Some typical examples of inlet and outlet protection used are:
−
Precast concrete units
−
Grouted sand bags (Figure 21)
−
Concrete (Figure 22)
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−
Reno mattresses and gabions (Figure 23)
−
Revetment mattress (Figure 24)
−
Spalls grouted or hand packed (Figure 25).
Inlet and outlet protection is to be installed as shown on the Drawings and in accordance with manufacturers’ instructions. Typical details for a gabion headwall are: 500 min
100 min 100 min
500 min
500 min
2000
300
Figure 31 – Gabion Headwall – Typical details
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Chapter 6 Maintenance of Track Drainage C6-1
General Good track maintenance and effective track drainage are closely associated. The stability and condition of the track and the formation is intimately related to the effectiveness of the drainage systems. The track’s drainage system must be carefully maintained. The consequences of poor or blocked drains can range from small areas of foul ballast to large washaways or embankment failures. Water must be drained away from the track as quickly as possible, so that it does not affect the track stability. Where sub-drainage work has been carried out; the outlets must be kept clean to allow water to run off. The cesses in cuttings must be kept formed so that the water will run at the toe of the batter. On banks the cesses must be graded away from the track. Where bog holes exist, ample metal ballast should be kept on hand to replace the continued loss of metal through fettling. The attention of the Team Manager must be drawn to this so that he may have sub-drainage work carried out, when practicable. Effective drainage is a major factor in minimising maintenance work necessary on welded track.
C6-1.1
Drainage Principles The basic principles of drainage are that drains will: Allow water to drain away: It is important that water is drained away from the track structure as quickly as possible. Keep water flowing: If there are low spots in the drainage path water will pond and will saturate the sensitive track structure and weaken the material in that area. Control the path of water: Water should not be permitted to flow from the drain into areas that will be damaged by water e.g. flowing into sink holes or from the cess back into the track because of debris in the cess. Control the flow rate of water: Water should not flow too slowly as to cause saturation (ponding) or too rapidly as to cause erosion. Reduce erosion: certain materials are prone to erosion and require additional treatment otherwise drains block rapidly or slopes become undercut and cause instability. Keep water as far away as possible: Where the countryside is very flat and recommended grades cannot be achieved, water should be drained away from areas that can be damaged by saturation e.g. allow water to pond at the railway boundary rather than the toe of the embankment.
C6-1.2
Indications of ineffective drainage The following are indications of ineffective drainage: −
Foul or dirty ballast
−
Pumping sleepers
−
Rotting sleepers
−
Bad top and line
−
Silted drains
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−
Pumping joints and crossings
−
Pools of water
−
Broken or blocked pipes.
If drainage is ineffective,
−
Look for the cause, and
−
Fix the problem.
Pools of stagnant water lying near the track must be drained and the problem that caused them rectified. The proper action is:
C6-1.3
−
Locate the problem
−
Drain the pools
−
Check all drains have proper cross-fall and grading.
Possible causes of ineffective drainage Possible cause of ineffective drainage are:
−
Broken pipes
−
Street gutters
−
Septic Tanks
−
Unlawful diversion of water by Property Owners.
To maintain good drainage the Team Leader must:
know where the drains are
know which way they flow
know where they discharge
clear any blockages immediately
−
repair any weak spots.
If Team Leaders cannot do the necessary work, they should:
−
report it to their Team Manager
−
request extra staff, material, or equipment.
Backhoes , bobcats, small bulldozers and dumpers are some equipment which can be used to clear drains.
C6-2
Surface Drainage
C6-2.1
Maintenance Considerations Maintenance operations carried out on surface drains usually fall into one, or a combination of the
following:
−
Weed control.
−
Removal of debris from other track maintenance activities.
−
Removal of sediment.
−
Regrading.
A build-up of weeds within the surface drain tends to slow the passage of water through the drain,
which, in turn, allows sediment to settle leading to a blockage of the drain. Such a blockage can
render a drain useless and lead to a decline in the effectiveness of other drains in the system. For
example, if a cut-off drain at the top of a cutting becomes blocked water may overflow the drain,
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run down the cutting face increasing erosion of the face and the cess drain will eventually block up due to the additional sediment load. Weeds may be removed using normal weed control practices. Sleepers and rails, for example, left in the cess drains after maintenance work, tend to act as dams allowing water to pond alongside the track and seep into the formation. This will also allow sediment to settle. Thus old sleepers and rails should be removed to a suitable dump at the completion of any track work. When a drain fills with sediment, whether it is due to a blockage or a flat grade, this sediment should be removed and the drain regraded if necessary. The type of equipment used to remove the sediment depends on the extent of the blockage and the accessibility (equipment used may range from a shovel to a gradall). Regrading is sometimes necessary due to scouring or to increase the grade of the drain slightly to reduce the amount of sediment that can settle in the ditch (channel). See Table 8 for a summary of Surface Drain Maintenance. Where cutting faces are exposed, thus undergoing unnecessary cutting face erosion leading to an acceleration of sediment build-up in cesses, these should be protected. Forms of protection commonly used are spray grasses, or seeding, sodding and shotcrete. Type of drain CESS DRAIN
Problems encountered
Possible remedies
Blockages - Weeds
Poison
- Old sleepers and railetc
Should be removed and cess regraded. Old sleepers and rails should be removed when replaced and not left lying in the cess drain, if not removed from site sleepers should be gathered up and disposed of.
- Other discipline infrastructure
Approach other disciplines about equipment relocation.
Spillages and Spent ballast.
Remove and regrade cess.
Blockages may lead to - Silt build up - Water ponding
Clean out cess drain and regrade if necessary.
- Overflow Uneven grades
Regrade cess.
Scour
May be possible to widen cess or regrade cess to decrease water velocity, if not the cess should be regraded and/or lined.
- Due to high water velocities Often found on down stream side of blockages CATCH DRAIN
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As above Animal (rabbit) burrows are also a problem in some areas
Eradicate or remove animals and fill in burrows.
Poorly graded
Regrade the drain.
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Type of drain
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Problems encountered Scour - Especially at outlets for catch drains above cuttings, where drains tend to be steep producing high velocities
Possible remedies Use more regular outlets. Therefore, producing less water at lower velocities at each outlet. Or regrade and/or line the drain.
MITRE DRAIN
As above for cess drains. Greatest problem is Scour
Regrade or line the drain. If necessary provide some means of retarding the flow out of these drains
GRADED SHOULDER
Water ponding
Regrade the shoulders so that they fall away from the track.
Table 8 - Summary of maintenance of surface drains.
C6-3
Subsurface Drainage
C6-3.1
Outlets Outlets are the most critical element of a subsurface drainage system because they are susceptible to events that can impede the free flow of water. The main concerns are blockages due to weed growth, siltation of the adjacent ditch or stream, debris from the track or slope and the activities of animals or man. A system of marking outlets of subsurface drains should be implemented to enable easy location of outlets. It is recommended that outlets and outlet markers be inspected and repaired, if necessary, as part of routine maintenance at least once a year. As with the inspection of other drainage system components this should preferably be carried out in the period of least rainfall.
C6-3.2
Pipes and Sumps Pipes and sumps are susceptible to blockages due to ballast and rubbish from the track, tree roots in search of water, siltation and pipe breakages or crushing. Sumps may be cleaned by either digging the sediment, ballast and rubbish out of the silt traps or by using a vacuum device (mainly used for deep sumps). Sumps filled with ballast are most effectively cleaned using post-hole shovels, but these are ineffective for the removal of fine noncohesive silt. Square nose shovels of varying widths are suitable only where sediment fills the silt trap. Where a sump is deeper than two metres it becomes too difficult to clean using shovels. In this case a vacuum device may be used. Once the sumps have been cleaned the adjoining pipes may be cleaned if necessary, by either rodding, hydroblasting or similar. Rodding of the pipes involves the pushing of a circular plug, of slightly less diameter than the inside of the pipe, through the pipe using flexible rods. Rodding is done working from sump to sump starting at the downstream end. Any sediment or other debris pushed out of the pipe is then cleaned out of the sumps. Hydroblasting involves the removal of sediment by using a low pressure, high volume water jet, since high-pressure low volume water jets tend to damage pipes. Hydroblasting is most effectively carried out using experienced Contractors. The process involved is as follows: Sections of the pipe network are cleaned from sump to sump working from the outlet pipe. Various nozzles are used to break up any encrustations and remove debris by either jetting it out into the sump or by relying on the volume of water and the grade of the pipe to create a self cleaning effect and remove any sediment.
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Once this operation is completed the sumps are cleaned either by the methods previously
mentioned or by sludge pumps.
This process is then repeated in the next pair of sumps and so on.
Care must be taken to replace any displaced sump grates or covers removed during the cleaning
and inspection of the drainage system.
See Table 9 for a summary of Subsurface Drainage Maintenance.
Problems Encountered
Type Of Drain Pipe, Aggregate Geotextile Filter and Sump Type Drain (Longitudinal Drains)
Sump Grates and Covers
Blockages:
Possible Remedies Clean out rubbish and ballast.
- Rubbish & Ballast - Silt
Hydroblast or rod pipe. Remove sludge with sludge pump or shovel.
Scour outlet
Provide scour protection and/or decrease water velocity.
Blocked by
Remove cover and or grate, clean sump if necessary. Clean and replace grates and cover. Remove rubbish etc. from site.
Rubbish and Silt
Aggregate & Geotextile Drains e.g. Blankets
Blocked Outlets
Outlets
Scour
Provide scour protection and or decrease water velocity.
Blockages
Clear away vegetation from outlet. Clear any other debris away from outlet e.g. spent ballast etc.
Remove vegetation. Clean outlets ensure no water ponds at outlets.
Table 9 - Summary of Maintenance of Subsurface Drains
C6-4
Typical problems and solutions This section looks at typical drainage problems, suggests possible reasons for their occurrence and practical maintenance solutions which range from simple cleaning to upgrading drainage.
C6-4.1
Cuttings Drainage problems are exhibited by:
−
Water ponding
−
Poor track alignment and level through the cutting
−
Pumping of mud up through the ballast
−
Rock pumping.
The main causes of these problems are:
−
Poorly graded cess drains.
−
Blocked cess drains i.e. drains silted up due to cutting face erosion or debris (e.g. sleepers
and spent ballast etc.).
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Foul ballast i.e. spillages from coal and wheat trains or mud causing the water to be trapped in the ballast. Another possible cause is the damming of water caused by the dumping of spoil by ballast cleaners at the ballast toe.
Another problem associated with cuttings is where cut off drains have been provided but not maintained. Thus water can pond within these drains resulting in the saturation of the cutting face which would lead to slipping, slumping or piping of the cutting face. This may also allow water to overflow the drains and run down the cutting face causing excessive cutting face erosion, which in turn causes the cess drain to silt up quicker. There are a number of solutions to these problems depending on the size of the cutting and the number of tracks. These are:
C6-4.2
Narrow or Steep Cuttings Depending on the severity of the problem it may only be necessary to clean, regrade the cess and ballast clean the problem section. The other alternative is to install subsoil drains. The cess is deepened and a subsoil drain installed, the ballast is then allowed to fall over the drain. Thus if the surface (cess) drain becomes blocked (i.e. silted up) the subsurface water is still being drained away from the formation. This system can also be used on multiple track, provided the formation is in good condition and graded towards the cess drains. Otherwise the formation may need to be reconstructed.
C6-4.3
Wide Cuttings In wider cuttings or if widening of the cutting is possible, the cess drains need only be deepened and widened so that water is drained out of and away from the track and does not prevent water flowing away from the track. This method should be used where easy access is available allowing regular maintenance to be carried out. Note: Cutting faces should be stabilised to reduce erosion and subsequent silting up of cess drains. For example spray grassing.
C6-4.4
Embankments The main drainage problems associated with embankments are; water being trapped in the ballast due to fouling of the ballast (either from spillages or mud) and the build up of spoils from previous ballast cleaning operations. Another problem is that of water ponding at the embankment base, which may lead to slips. This water may cause saturation of the embankment base consequently causing further consolidation and settlement of the embankment. To prevent water being trapped in the ballast, leading to formation failures, the shoulders of the embankment must be kept clean and graded away from the track. Thus windrows of spent ballast must not be allowed to build up on embankment shoulders. Depositing ballast cleaning spoil over the side of the embankment stops water being trapped in the ballast but can cause water to be trapped in the embankment itself. The spent ballast tends to from an impermeable layer over the outside of the embankment. Catch drains must be installed and maintained such that water is prevented from ponding at the embankment base. An alternative to catch drains in flat areas is to grade surrounding ground away from the embankment such that if water does pond in the area, it is away from the embankment base. At areas of heavy seepage through embankments, a transverse subsoil drain should be installed to drain the water from the embankment, thus reducing the possibility of embankment saturation and any resulting problems.
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On multiple tracks where drainage problems have been encountered it may be necessary to install a transverse drain with suitable outlets to effectively drain water from the ballast. Note: Embankment faces should be stabilised to reduce erosion problems (e.g. spray grassing or sodding or geotextile, etc.).
C6-4.5
Soft Spots or Bog Holes Because this condition is often the result of water collecting in depressions in the formation caused by inadequate or poorly maintained drains the first consideration should be to upgrade or clear existing drainage. The provision of suitable drainage to preserve the stability of the formation is of prime importance.
The disposal of the impounded water from these depressions is achieved by excavating to the
lowest level and providing suitable permanent outlet drains.
Before deciding the actual method of treatment, the local conditions must be investigated. The
objective of the investigation is to try and determine the source of the water and to obtain the depth
of the water pocket or depression.
To investigate a soft spot, trial holes are sunk at about 2m intervals. This will determine the depth of ballast and soft formation. This enables selection of the best type of drainage system or solution to the problem. The procedure to follow in the solution the problem is as follows: 1. Determine the position and depth of the outlet drain or 'tap' drain by using trial holes to locate the depth of ballast or the soft area. 2. Excavate and remove the 'soft spot' and foul ballast. The lower level of the trench for any sub drains used must be graded longitidinally at least 1:100 toward the outlet drain. Sub drains should be lined or covered with a geotextile fabric and filled with clean new ballast. 3. Cess drains are also upgraded so that surface water will not penetrate the treated area upon completion of the work. Where possible, they should be widened and graded uniformly to the mouth of the cutting. This will help in allowing the water to run freely away. 4. If the capping layer has been disturbed it is then restored with crossfall angled towards the drains. 5. The track is restored with 'clean' new ballast and resurfaced.
C6-4.6
Scours and Washaways During heavy and prolonged rain, the normal drainage channels provided may not be able to deal with the extra water flowing through them, with the result that flooding occurs. In flat country, embankments may become submerged and saturated. If the water level rises uniformly on both sides of the bank, there will not be a great amount of water flow. As a result, little damage will occur. If, however, the flooding is confined to one side of the line, bridge and culvert openings will be liable to scour. Should the water run over the top of the track, very serious damage can result. The amount of damage will be dependant on the velocity or rate of flow of the water. Any steps taken to reduce the velocity will, therefore, assist in reducing damage. The danger point is reached as water first commences to trickle over the formation. Scouring then starts, first in the ballast and then in the formation. If there is a large difference in the water levels on the two sides of the bank, the velocity will be high and damage extensive.
C6-4.6.1
Temporary Repairs During heavy flooding, washaways may be numerous. They may range from small sections of ballast washed away to deep cuts where the whole embankment has been removed. The method of affecting temporary repairs will depend on the nature and size of the washaway and also the materials and equipment available. If the ballast only is scoured out and it is not possible to get ballast to the site, quick repairs may be made by redistributing the remaining ballast. This will lower the track into a long 'slack' and is only
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a temporary measure to restore traffic. More permanent repairs must be completed as soon as possible. Where shallow scouring of the formation occurs, continuous sleeper pigsties may be used. For deeper scouring, pigsties, trestles and temporary beams will be required. Permanent repairs will then require the closure of the track and reconstruction of the embankment.
C6-4.7
Slips This type of earthwork failure comes within the experience of nearly every person associated with track maintenance. They need not be large to cause serious damage and are very dangerous in that they can occur suddenly and without warning. It is desirable, in the initial construction of the track, to avoid unsuitable soils. However, track staff are generally involved with tracks constructed for many years. As such, conditions must be dealt with as they are found. Terracing and flattening of slopes will assist in bringing about stable conditions. Cuttings, in soft material or in slopes liable to fail, may be widened to provide space for falling debris clear of the track. Material removed from cuttings should not be placed on or pushed over embankment sides without prior investigation of the embankment stability. Embankments can only be widened using the correct procedures. Advice on the appropriate batter slope, terraces and procedures for the widening of embankments should be sought from the Geotechnical Services Section. Small slips may be foreseen and prevented by the removal of loose material or the building of some form of protective structure. The removal of only the 'toe' of a slip will lead to increased sliding. When it is necessary to clear the toe, only the minimum quantity to permit the passage of trains should be removed. Mud flows, which result mainly from heavy rainfall, cannot always be foreseen and prevented but continual maintenance of top drains will assist in reducing their incidence. Slips may be of several types or include features of each type.
C6-4.7.1
Flow Movements The soil material of a hillside or side slope may become so saturated with water that it moves downward in the form of a mud flow. The rate of flow may be slow or rapid depending on the degree of saturation and type of material. The slopes from which the flow starts need not be steep if excess water is present. The potential effect of this type of slip is to cover the track, push it out of line or destroy any form of support or retaining wall.
C6-4.7.2
Shear Failure Sometimes an embankment or hillside is composed of soil without any great strength or cohesion between its particles. It may be standing too steeply and cracks may develop which will permit the entrance of water. Movement or a large part of the slope takes place slowly at first but can become very rapid as complete failure takes place. This type of slip may occur at any time, even many years after the railway is constructed. The effect on the track is seen as a depression if the movement is minor or a total loss of support if major movement occurs.
C6-4.7.3
Slope Adjustment This is a natural occurrence due to erosion. Quantities of spoil or rock fall away from the sides of cuttings and fall onto the track. They may be composed of fine material or rocks that are large enough to derail trains.
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Protection against the damage can be afforded by periodically removing any loose stones and by the provision of a wide bench at the toe of the cutting in which debris may collect clear of the track.
C6-4.8
Platforms The main problem associated with platforms is the ponding of water that consequently causes formation failures, exhibited as poor track alignment, pumping sleepers and bog holes. The solutions available depend upon the severity of the problem. These are: −
Clean all sumps and pipes
−
Install a suitable drainage system in the six foot
−
Recondition track and install subsurface drainage system
−
Completely excavate problem area and replace with densely compacted fill up to the next formation level, then provide a 150mm compacted granular capping layer and 300 mm of ballast cover. During reconstruction install a subsurface drainage system.
Also at stations with island platforms there is often a problem with water ponding at the ends of the platform. This can be remedied by placing a sump in the six-foot connected to an existing drainage system or suitable outlet. Note: Runoff from station buildings and platforms may be piped into sumps. This provides relatively clean water which can be used to help flush drainage systems.
C6-4.9
Turnouts With the increased axle loads and cyclic forces exerted on turnouts it takes very little water for them to start pumping mud up through the ballast, consequently fouling the ballast and compounding the problem. Some solutions to this problem are as follows: −
Deepen and widen the cess drains on each side to drain water from the ballast and keep it clear of the formation
−
Install subsurface drains under problem areas during turnout reconditioning or renewal. Major problem areas are under heel blocks and crossings. These are points where the most pounding (greatest impact load) tends to occur.
In come cases during turnout and crossing renewals asphaltic concrete has been used as a capping layer to help increase the impermeability of the formation thus giving it a longer life.
C6-4.10
Yard Drainage The problems associated with yard drainage are similar to those of any other track work except on a larger scale. Where on most lines the drainage must cater for between one and four tracks in yards there are usually many more. Also yards tend to be constructed on very flat areas, thus there is very little fall available for surface and subsurface drainage systems. The simplest solution for any drainage problems in yards is to clean and regrade cesses and provide regular outlets in the form of sumps such that the best possible grades can be applied to the surface drains. The most effective method is to have the formation graded as shown in Figure 31 below.
Figure 32 - Typical "saw tooth" formation used in yards Subsurface drains are located at the low points. If large flows are expected it may be necessary to install carrier pipes. Carrier pipes may be placed at a deeper level thus allowing the grades of subsoil drains to be increased between sumps.
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Subsurface drains
Carrier pipe
Figure 33 - Carrier Pipe Arrangement
C6-4.11
Bridge abutments and retaining walls Unless adequate weep holes are installed during construction and kept clear by routine maintenance, weep holes tend to block, trapping water behind the abutment or retaining wall. This causes saturation of the earth (fill) behind the walls, which can lead to further consolidation and settlement of the fill. Weep holes are required at and above the capping layer level as well as at the base of a wall. Weep holes should also be located at regular intervals down the wall, thus if the bottom holes become blocked the upper ones can still allow some water to escape. Existing weep holes should be cleared during routine bridge maintenance. New holes should be bored through the wall if no holes exist or the existing holes are inadequate, especially if there are no weep holes present above the capping layer level.
C6-5
Preparation for Flooding
C6-5.1
General Each Region is to have an emergency plan for dealing with major flooding that would effect train operations. Major flooding can occur with little warning and quick action may be necessary without time to prepare. The "Flood Plan" is to be documented and regularly updated. Copies are to be issued to each Team Manager and other senior staff. In particular, a copy is to be part of the "Handover Notes" for relief officers. The Regional staff should be the railway source for forecasting the effect of a flood on railway facilities and be the adviser to Network Control. The Civil Maintenance Engineer is to arrange this service when a flood is forecast.
C6-5.2
Historical information The collection of data during flooding is most valuable in planning measures which will reduce or avoid damage by future floods. The heights of water levels at bridges, culverts and on railway embankments should be marked so that flood levels may be recorded. At large bridges, the water level may be different at each end or on up and down stream sides. Levels at all of these points should be recorded. Any appreciable difference in the up and down stream flood levels at a bridge may indicate an inadequate waterway. The records of previous floods in each river in the Region are to be kept up to date. Frequency and severity of flooding are usually available on Working Plans and office files. Other instructions require all flood heights to be recorded. Local Councils and other local bodies can provide a wealth of information on flood heights that will allow up river peak height information to be related to timing and severity of railway bridge flooding levels.
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Local papers and local residents can also advise on the time the river takes to rise, water movements and other essential local knowledge. Bureau of Meteorology Rainfall patterns assist in assessing runoff rates, saturation figures as well as river peaks and times. From all available information a river flow chart should be prepared that will provide an accurate forecast of the effect of future floods in the river systems on railway facilities once upriver reports are received.
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Chapter 7 Documentation Requirements C7-1
Introduction The aim of this section is to provide a guide for external consultants in the preparation of design drawings and hydrology reports for minor track drainage projects within the rail corridor. It also covers external party development works discharging onto or through the rail corridor. The requirements are also applicable to RailCorp field staff doing track drainage design. This guide is provided to achieve standardisation of documentation associated with track drainage design and external works discharging onto the rail corridor. All documentation is to be retained on the project design file. Minor drainage works within the railway corridor include open cess, pipes, pits, covers such as lobster cage, and minor under track drainage openings.
C7-2
Review Process When the drainage design/hydrology report is at minimum 90% completion, drawings/reports are to be submitted to RailCorp’s Design Delivery Manager (DDM), who will forward them to the Bridges and Structures Design Section for review. The review will be conducted in two parts: 1.
Drawing review
2.
H ydrology/hydraulic review.
The following documentation is required for this process: Drawing review: −
1 hardcopy set of prints - A3 size (or softcopy pdf files).
Hydrology/hydraulic review: −
2 hardcopies of a Hydraulic/Hydrology report (or softcopy pdf files). Where the nominated Civil reviewer determines that a full hydrology report is not required, then a summary document shall be prepared as a minimum – refer to section C7.4.
−
A softcopy of the hydrology/hydraulic computer design file (eg ‘Drains’ drn file) or hand calculations shall be provided.
The time for Railcorp to undertake the review is highly dependent on the availability of RailCorp staff and their existing work commitments. Typically this may be 2-3 weeks but may extend up to 6 weeks in some instances. It may be a requirement for the Reviewer to undertake a site inspection, in which case, it may be necessary for the consultant to attend an on site meeting. The Reviewer will look at the information provided and highlight any changes/additions/comments that may be needed to meet RailCorp requirements. Once acceptance has been given (and all modifications incorporated), then the consultant/designer must provide final acceptance documentation. For acceptance and final sign-off, the following documentation will be required: −
1 signed set of drawings (A1) size with all necessary signatures.
−
CAD drawing files in MicroStation Version 8 format and on labelled CD.
−
2 signed copies of the final hydrology report.
−
A softcopy of the final hydrology/hydraulic computer design file.
A senior member of the Bridges and Structures Design Section will sign the documentation as ‘accepted’ for use by RailCorp. The drawings will then be registered in the Plan room. The DDM
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can then arrange copies of the approved drawing for distribution to the Consultant and appropriate RailCorp field staff. RailCorp acceptance signatures on drawings prepared by Consultants designate only that the drawings appear to be consistent with the requirements of the design brief and that the presentation is satisfactory. No dimensional, drafting or design check will be undertaken by RailCorp. The responsibility of the structural adequacy, safety, compliance with codes & legislative requirements and dimensional accuracy remains with the consultant. Note: Any costs associated with undertaking changes requested in the review process will be borne by the Consultant.
C7-3
Drawing requirements All drawings are to comply with the relevant sections of the RailCorp CAD and Drafting Manual – ED 0022P, ED 0026P and ED 0027P. Typically, most rail drainage projects are site specific in that they have different site constraints, varying terrain and unique rainfall catchments. For this reason, RailCorp has not developed standard drawings. However, it is fair to say that many details of track drainage remain generic. The following aspects are considered the minimum requirements that should be detailed on track drainage drawings. General −
All drawings are to be completed using CAD (Microstation or AutoCAD). There is to be only one drawing sheet per CAD file.
−
Drawings are to be detailed using standard RailCorp drawing sheets (A1 size). Electronic file of the standard RailCorp drawing sheets in dwg format will be provided to the Consultant
−
Each drawing is to have a unique RailCorp drawing number (CV No’s). These numbers will be supplied on request. Note: if more drawings are required than originally requested, then additional numbers must be requested. These numbers probably will not be a continuation of numbers previously given.
−
The RailCorp drawing numbers shall be used for cross references and not drawing sheet number or consultant internal filling numbers.
−
Title blocks are to be filled out to RailCorp Standard as detailed in the CAD Manual.
Plan −
Drainage layout drawn at a minimum scale of 1:200 with Sydney shown on the left.
−
The layout shall include identification or marking of drainage pits/sumps eg pit P1, P2 etc.
−
All railway tracks (including turnouts, crossovers and sidings) to be shown and labelled eg Main West - Down
−
Kilometrage marks to be shown along the track – say at 20m centres. Text labelling at even 100m centres (20.100km). Note: OHWS structure numbers may not coincide with track km.
−
Show the North point.
−
Indicate and label railway boundary line.
−
Show the top and bottom of cuttings, embankments, drainage channels, depressions etc.
−
Show and label trackside furniture - if applicable (eg signal footings, signal troughing, air lines, train stops, services, face of platforms, retaining walls, bridge abutments & piers etc).
−
Show and label any applicable surveyed items (eg trees, power poles, nearby buildings, edge of roads or access roads etc).
−
Show locations of any external services (as determined from a dial before you dig requestsubmitted by the consultant).
−
Existing drainage to be indicated and labelled (dotted if they are to be removed).
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−
Proposed drainage with dimensions of extent, pipe size/type/class. Arrows indicating flow direction. Each pit to be labelled (e.g. P1).
−
Extent of scour protection (dimensioned and labelled fully).
−
Pipe Jacking - temporary excavation lines shown and pipe jacking direction indicated.
−
OHWS shown with footing outline and structure number indicated. Note: OHWS comprise of a pedestal and either piled or spread footing base. Normally only the pedestal is visible. RailCorp Bridges and Structures Design Section personnel may be able to help determine the footing size/type if a structure number is known.
The plan shall be drawn from and based on a detail survey. However, at the discretion of RailCorp (due to time or budgetary restraints), a schematic layout such as a “track diagram” may be inserted into the drawing. If a “track diagram” is used, then the following note is to be included alongside (in a highlighting box): 1. This plan has been taken from track books and is not to scale. 2. The effects of track curvature and clashes with existing OHWS footings or trackside furniture is to be confirmed on site prior to ordering materials and/or construction. 3. The possible effects of undermining of existing structures have been investigated and are covered in the design.
Locality Map −
Such as a street directory format showing the general area is to be included.
−
Label “From Sydney” & “To Country” at the edge of the map.
−
Show North point.
−
Circle and identify “Site of Works”
Typical Sections −
Are to be drawn at a suitable and legible scale (usually 1:20 is adequate)
−
Show the track, ballast and cross fall of the track formation
−
Show nearest track and dimension the offset to the centreline of the drainage system.
−
Dimension the depth below rail of the pipe system and the pipe cover to ground surface.
−
Indicate width of trench, pipe type/size, geofabric type and fill and bedding material.
Dimension and label compaction layers.
−
If an open channel is adopted, fully dimension the channel and label any scour protection. A table can be incorporated if the channel size varies along the length.
−
If different methods of pipe installation are covered, then a typical section is required for each method (eg cess pipe installation different from undertrack pipe installation)
Longitudinal Sections (for pit/pipe & open channel)
−
A separate longitudinal section is required along all pipe/drainage lines.
−
Draw at a suitable scale (vertical exaggeration can be used to highlight grades)
−
Table along the bottom of the longitudinal section with headings indicating ‘Track km’, ‘design
rail level (low rail)’, ‘cess level’ and ‘pipe invert level’.
−
Indicate track km, rail levels and cess levels at a minimum of 20m centres and at pit locations.
−
Indicate pipe invert level at all pit locations.
−
Indicate grade and extent of pipe runs/open channel.
−
All levels nominated shall be to AHD. Where assumed level is adopted the assumed benchmark must be clearly identified.
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Additional Details Include any additional details that are essential for the construction of the project. These may be
individual details or separate drawings and may include items such as (but not limited to):
−
How new pipes are to be joined in with existing drainage.
−
Energy dissipating device details.
−
Scour protection details.
−
Pipe jacking collaring.
−
Detention basin details.
−
Lobster pot details.
−
Temporary support of existing structures.
Pit Table A pit table is to be included and shall be set up in the following format Pit No
Pit type
Riser
Top
P1
# 1/ 600 sq. x 1200 deep (internal)
# 1/ 300 high riser
1/ 150 high LID.
# 1/ 150 high riser
1/ HD galv. cast iron grate. 1/ Ballast Cage
# - designates step irons required in pit Notes −
Design Criteria (e.g. Design: Average Recurrence Interval (ARI) of 50years, Loading: pipes designed for 300LA + DLA train live load etc.)
−
Pipe/pit notes.
−
Any other notes particular to the project (eg shotcreting)
References (Drawings) −
The first drawing in the set is to reference all other drawings. The remaining drawings need to refer to the first drawing and any other drawing that is referred to in the details on that sheet.
Typical Example Drawings Examples of typical drainage design drawings are in Appendix 5.
C7-4
Hydrology/Hydraulic Report requirements Where a hydrology report is required, the following format is recommended and the items listed are considered the minimum requirements to be incorporated. −
Document Control Table – To incorporate the revision number, revision date, revision details/change and the relevant QA signatures.
−
Table of Contents.
−
Executive Summary (for large reports only).
−
Site description & background.
−
Catchment Details – provide a description of how the catchment has been divided up. For large projects where multiple systems operate and/or catchment break-up is hard to define, then an Illustration/map will be required.
−
Design Methodology – Describe the concept of the design, the software program utilised and a description of the other options considered.
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Hydrology – Describe any relevant hydrology issues and include a table of the hydrologic parameters adopted for the analysis. Example Hydrologic Parameter
Value
Design ARI 1 in 50 years Typical hydrology parameters as adopted in the ‘Drains’ software are: paved (impervious) area depression storage, grassed (pervious) area depression storage, soil type, Antecedent moisture content (1-4), Annual Recurrence Interval ARI, Storm duration range considered, soil permeability %. −
Hydraulics – Describe any relevant hydraulic issues and include a table of the hydraulic Parameters adopted for the analysis. Example Hydraulic Parameter
Value
eg RC pipe Manning’s No 0.002 Typical hydraulic parameters as adopted in ‘the ‘Drains’ software are: minimum pipe slope, minimum pit freeboard, minimum fall across pits, minimum pipe diameter, pit blocking factor, minimum pipe cover, pressure loss coefficients, maximum ponding depth, maximum ponding volume, pipe Manning’s No). −
Analysis Results – Describe the results of the analysis and include a results summary table. In some cases (such as external developments), it may be a requirement to compare various Options or compare between the pre-development and post development scenarios. Example Drainage line
Total Catchment area
Peak Discharge at outlet
Max velocity
Storm event
Pipe 5
1500 m2
40l/s
1.2m/s
ARI 50, 45min storm
(critical case) The table heading and values should be modified to incorporate the type of system being modelled and the critical output relevant to the project. −
Conclusions.
−
Appendix A – Output from computer modelling (from ‘Drains’ this would both ‘input data’ and ‘Results’)
−
Appendix B – Photographs of the site.
For the majority of hydrology reports the above details will be satisfactory. For more complex hydrology scenarios, it may be required to incorporate additional information. Typical examples of this may be when dealing with detention basins, considering backwater effects or examining complex flooding interactions. At the discretion of RailCorp (due to RailCorp time or budgetary restraints), a summary document (report, letter or e-mail) incorporating major aspects of the items above, may be submitted in preference to a report. This will be determined by the Design Delivery Manager (DDM) at the commencement of the project.
C7-5
External party development discharging onto or through the rail corridor The Developer shall provide the minimum supporting documentation as detailed below:
C7-5.1
Hydrology/Hydraulics report A hydrology/hydraulics investigation report shall be prepared by a professional services organisation with the appropriate expertise. The investigation and analysis shall include any
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possible impacts of any additional discharge downstream or backwater effect upstream. This is to include discharge into Council stormwater systems. The report shall be set out as per C7-4, and shall be structured to compare between predevelopment and post-development scenarios. The report shall look at an Average Recurrence Period (ARI) of 50 years and should investigate a range of storms from 5 minutes to 24-hour duration. Note: RailCorp will accept reports done for ARI 100 years (as stipulated by some council’s) as long as the results satisfy RailCorp requirements. It is RailCorp’s policy to reject any submission where the development will adversely affect discharge rates onto or through the rail corridor. To control this, the developer may be required to incorporate a retention/detention system within the developer’s property. Such a system must be covered in the hydrology/hydraulics report. It will also be the consultant’s responsibility to submit a ‘Long-term Maintenance Management Plan’. It is RailCorp’s policy to reject any submission where the development will increase scouring potential within the railway boundary. A drainage solution particular to the site may be required to effectively disperse flow. Alternatively, provision of scour protection may be required. Where the existing track drainage is found to be inadequate to accommodate the site discharge, the developer shall document the upgrade of the track drainage required at their costs. The costs (to be borne by the developer) shall include of upgrading of the RailCorp drainage system.
C7-5.2
Drawings Where upgrading of the RailCorp track drainage system is required, or additional drainage works are required within the railway boundary, the documentation shall be prepared in accordance with the requirements specified in C7-3. Where the developer confines all drainage works to within their property, then a layout plan shall be supplied that conveys the overall stormwater drainage system. This shall include any pipes/pits/basins/channels/downpipes and is to include the outline of the proposed dwelling and ground contour lines (including any ground level survey points taken). Any labelling of pipes and/or pits shall conform to the labelling conducted in the hydraulics/hydrology report. All pipe inverts shall be clearly identified in plan or on cross sections. Any non-related information shall be filtered out. For construction works carried out within the railway boundary, work-as-executed drawings are to be submitted once works have been completed.
C7-5.3
Long Term Maintenance Management Plan Where a developer incorporates a detention/retention system to control discharge, then a ‘Longterm Maintenance Management Plan’ will be required. This shall detail the actions and frequency of inspection and maintenance tasks to effectively maintain the system over its design life. Responsibility shall be clearly defined in the Maintenance Plan eg who is responsible for the nominated inspection and who is responsible for carrying out the maintenance tasks. Any costs incurred by RailCorp as a direct consequence of failure of the stormwater system will be passed onto the developer/owner.
C7-5.4
Other considerations The Developer shall seek the appropriate approval from the affected Council or other relevant Authorities & parties. The cost of design, documentation and construction for any works within the railway boundary shall be born by the developer. The developer must ensure that works are carried out in accordance with railway safety requirements with appropriate RailCorp safety accreditation for all workers.
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Appendix 1
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Flow Charts Flow Chart 1 – Overall Design Process
1. 2. 3. 4. 5.
Design Investigation. Objective Information required Collection & study of existing information Site investigation Catchment estimation
Drainage System capacity 1. Recurrence interval 2. Design system
Rational method Section C4-4.3
Peak surface runoff flow
Is the drainage system required a surface or subsurface system? Surface
Subsurface
Flow chart 2
Flow chart 3
Produce any drawings and tables necessary for system installation
Design stage complete proceed to construction phase
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Flow Chart 2 – Surface Drainage Design From C3.6 Calculate the peak flow rate QPF
Determine the local soil type such that the maximum permissible velocity and roughness (Table 3) can be established.
Determine the slope from the preliminary investigation survey (Standard is 1 in 100).
Select trial channel size from Table 4.
Calculate the maximum flow rate for the selected trial channel size (Q1)
yes
Is Q1 ≈ QPF?
no
Check the water velocity (V1)
Is the velocity less than the maximum permissible velocity? Table 5
no
Provide either a larger channel or line the drain
yes The channel size & water velocities are satisfactory
If new lining was chosen, then the cost of the lining versus a larger unlined channel should be compared.
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Flow Chart 3 – Subsurface Drainage Design From C4-6.1 Calculate the peak surface runoff (QR)
Is QS =0?
no
Carry out a hydrological study to establish Qs or estimate a value for QS
no
Estimate the value of QC from the size of the upper drain & approximately how full it flows
yes
Is QC =0? yes
QPF = QS + QC + QR (equation 1)
pipe
Is the subsurface drain a pipe or aggregate drain?
Determine the slope of the drain
Determine the slope of the drain (Standard is 1 in 100)
Size pipe for all pipe materials (min dia 225mm) Select pipes from Table 6 such that max flow > QPF determined from eqn 1
Select the size of the aggregate
no
Is the
flow rate in the
pipe acceptable?
yes
aggregate
Choose a value for K from Table 7
Once the required flow is known, the drain area required can be calculated using equation 8
Calculate the strength of pipe required (C4-6.1) Select other drainage components eg. fabric etc (C4-2.3) Compare the cost and availability of each type of pipe
Select a pipe
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Drainage Design Checklist The following checklist is used by RailCorp’s Bridges and Structures Design Section when undertaking track drainage design. It provides a useful guide for consultants and RailCorp field staff.
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Checklist D06
Drainage Design & Investigation Checklist Project Identification Location
Line
Details
Project Number or Identification
File
Design Delivery Manager
Delivery Plan prepared
YES
Target Dates
Documentation
In House
Deliverable requirements
Hydrology/Hydraulics Report Detailed Design Technical specification Review of External design/report
NO External
Investigation Report Scope of Works
Prepared by: Scope of Work/Project Brief − − −
What type of drainage is it? (i) Track (ii) Bridge – UB/Culvert (iii) External Party Development Has a scope of works been provided for Civil Works? Has a project brief been provided? − Have the key design parameters been defined in the scope/brief? − Are Mandatory Legislative or Regulatory requirements defined in the scope /brief? − Have any validation methods been established in the scope/brief? − Is a Technical Maintenance Plan (TMP) required? − Has functional and performance requirements been identified by the client? − Have Interface requirements been scoped (see below)? Are there any future proposals that has been identified (eg– access road, embankment widening, quadruplication, turnbacks, upgrades, track lifts etc).
(i)
(ii)
(iii)
YES YES YES YES
NO NO NO NO
YES YES YES YES YES
NO NO NO NO NO
Do installation or maintenance manuals need to be developed or changed?
YES
NO
Do you know what the operating conditions are? − Class of line − Speed − Maximum Axle load − Operation (inspection/maintenance regime etc) − Usage factors such as numbers of trains − Will the configuration change affect the conditions of operation?
YES YES YES YES YES YES
NO NO NO NO NO NO
Is training required prior to the installation of the design? Have all the stakeholders (both internal & external) been identified.
YES YES
NO NO
−
N/A N/A N/A N/A
N/A N/A N/A N/A N/A
Discipline Interface Track − −
Impact on track vertical & horizontal alignment (eg Is there a need to lift or move the tracks)? Are design track levels (low rail) known?
YES
NO
YES
NO
YES YES
NO NO
Geotechnical − −
Are founding parameters required for drainage design? Is there any possible stability concerns with adjacent structures or embankments?
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Survey − − − −
Is a detailed survey scope required? Is additional survey required to define the catchment area (eg cross sections, additional points) Do existing drainage systems and services need to be identified? Items required survey (cross out/add as appropriate) – exist drainage, pipe sizes, locations of pits, invert levels, inlet/outlet , cess levels, rail levels, existing OHWS+footings, visible services, banks, ballast edge, road edge, site markers, survey pegs, fenceline, trees, surface levels, define wingwalls, water level, local depressions, sketches
Electrical − Are there any Electrical requirements such as electrolysis, transmission lines & other services? Services − Has RailCorp internal services searches been conducted? − Has ‘Dial Before you dig’ external services searches been carried out? − Does it look possible that conflict will exist with structure footings External Bodies? − Has external hydrology reports been carried out in the area (eg local Council/previous reports)? − Are external bodies required to be involved? If Yes, then circle or itemise:
Local Council development Consultant
RTA
………………
EPA
Water Authorities
………………
………………
NO NO
YES YES
NO NO
YES
NO
YES YES YES
NO NO NO
YES
NO
YES
NO
YES YES
NO NO
Land Owner External ………………
Will any proposed configuration changes − Impact on RailCorp’s accreditation with Minister of Transport?
−
YES YES
Require approval from external bodies (EPA, RTA, Water Authorities, Local Councils etc)?
Site Data Site − − − − − − −
Is the proposed works located in an (i) embankment, (ii) cutting or (iii) open track Project type: (i)Renewal / (ii)Refurbishment (UB & Culvert) or (iii) Upgrading for Track Drainage Is there possible impact with existing structures – OHWS, Signal Gantry, Bridges, footings (eg alignment conflicts, undermining of footings, embankment stability concerns)? Site access – is there an existing access road? Is there surrounding drainage systems? – Local Council, RTA, private parties Is there possible scouring concerns or evidence of site scouring? Are details (drawings) of existing drainage available?
(i) (i)
(ii) (ii)
YES
NO
YES YES YES YES
NO NO NO NO
YES YES YES YES YES YES
NO NO NO NO NO NO
(iii) (iii)
What are the Physical Interfaces with Other Property Owners/Stakeholders − − − − − −
Road crossings (including private crossings) Interface between earthworks and other properties Drainage flow to other properties Installations such as pipelines laid within the corridor Private sidings and bridges Other statutory authority requirements eg environment?
Hazard & Risk Identification and Analysis Hazard sources from −
Normal operation
YES
NO
−
Environment
YES
NO
−
Equipment failure
YES
NO
−
Improper use or maintenance
YES
NO
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Risks to − Maintenance or Construction staff
YES
NO
−
Public
YES
NO
−
Operators
YES
NO
−
Other equipment
YES
NO
−
Environment
YES
NO
Has the Design/Analysis considered the effect of potential hazards and risks during −
Construction, including any temporary works required as part of the project
YES
NO
N/A
−
Maintenance
YES
NO
N/A
−
Operation
YES
NO
N/A
−
De-commissioning and disposal
YES
NO
N/A
YES
NO
N/A
Has a proper hydrology & hydraulics calculations been carried out by staff with the proper Engineering Authority (including correct design parameters)?
YES
NO
N/A
For complex hydrology studies – has an external service provider been nominated?
YES
NO
N/A
Have possible mitigation measures been identified and documented?
Design and Documentation Checklist Hydrology & Hydraulics
Hydrology report / Investigations Has the following information been documented −
Document Control Table (revision no, date, details, signatures)
YES
NO
N/A
−
Site Description & Background
YES
NO
N/A
−
Options for refurbishment or renewal
YES
NO
N/A
−
Catchment Details
YES
NO
N/A
−
Design methodology
YES
NO
N/A
−
Hydrology Parameters adopted
YES
NO
N/A
−
Hydraulic Parameters adopted
YES
NO
N/A
−
Other design input (eg survey, recorded flooding, measured values, consultation with councils or authorities)
YES
NO
N/A
−
Analysis Results
YES
NO
N/A
−
Conclusions & Recommendations
YES
NO
N/A
−
Recommendation and concurrence by stakeholders
YES
NO
N/A
Comments:
Detailed Design drawings Has the following information been documented −
Location & description and extent of the drainage works
YES
NO
N/A
−
Drawing sheets and title block to RailCorp current standards
YES
NO
N/A
−
Plan view (Sydney on the left, layout of drainage, existing drainage, banks/depressions, all tracks labelled, nth point, boundary line, OHWS, services, scour protection, flow direction, survey items etc)
YES
NO
N/A
−
Locality Map
YES
NO
N/A
−
Typical sections(offsets to rail, depth to rail, cover to pipe, trench details, compaction layers, geofabric, scour protection, pipe labelled,)
YES
NO
N/A
−
Longitudinal Section along each pipe run (includes, track km, design low RL, cess level, pipe invert levels, grades)
YES
NO
N/A
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−
Relevant notes – design criteria, reference to appropriate Standards and manufacturers.
YES
NO
N/A
−
Drawing References
YES
NO
N/A
−
Additional details (join with existing, energy dissipators, scour protection, pipe jacking, detention basin, lobster pots, temporary support etc)
YES
NO
N/A
−
Specific maintenance requirements eg retention basin – responsibilities and frequency of silt removal
YES
NO
N/A
Does the design document and the information it contains complies with the standards?
YES
NO
N/A
Does the design reflect sound engineering practice?
YES
NO
N/A
Have all known relevant project constraints have been considered?
YES
NO
N/A
Is this document fit for purpose?
YES
NO
N/A
Is it suitable for construction use?
YES
NO
N/A
Is it Suitable for record (plan room) purposes?
YES
NO
N/A
YES
NO
N/A
Are dimensions correct?
YES
NO
Is the drawing to scale?
YES
NO
Is the designer's intention clear?
YES
NO
Is sufficient information given?
YES
NO
Practicality
Can the work be constructed as efficiently as possible?
YES
NO
Consistency
Is the drawing consistent with existing drawings of the same type?
YES
NO
Does the design generally comply with the RailCorp track drainage guide? Drawing Check (Reference – Part 4.8 & 4.9 EM0323) Accuracy
Clarity
If not, can the change be justified?
YES
NO
Standards
Have relevant drafting standards and practices been adhered to?
YES
NO
Is the drawing presentation consistent with RailCorp drafting standards
YES
NO
References
Are all the necessary cross-references included?
YES
NO
Status
Has the drawing status been updated? Eg from tendering & construction
YES
NO
Title
Is the drawing titled according to RailCorp practice?
YES
NO
Corrections
If corrections have already been marked on a previous check print held by the checker, are they included in the current print?
YES
Distribution
Have the drawings been distributed to the relevant stakeholders by the DDM?
YES
NO
YES
NO
NO
N/A
N/A
Verification and Approval The drawing has been signed by the drafter, drawing checker and designer Drafting Checker
Signature
Printed Name
Date
I certify that I have completed the drafting check The drawings reflect the design intent, details and completeness. Designer
Signature
YES Printed Name
NO
Date
I certify that I have completed all required actions.
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Have independent actions have been taken to verify the design as detailed on the drawings Independent Verifier
Signature
Printed Name
YES
NO
N/A
Date
I certify that I have completed an independent design check The design, drafting and checking functions have been carried out by people with appropriate Engineering Authority
YES
NO
The design and drawing reflect sound engineering practice
YES
NO
Reviews at progressive stages have been carried out with the client, to ensure that the design takes into account the client’s needs, the functional requirements and constraints of all relevant codes, standards, regulations, practices and statutory requirements.
YES
NO
N/A
Comments:
The drawing is satisfactory for construction purposes
YES
NO
The design phase for the discipline is complete
YES
NO
YES
NO
Has the relevant information been entered in Bridge Management System (DAD)? RailCorp Engineering Division objectives and standards have been applied Approver
Signature
Printed Name
Date
Signature
Printed Name
Date
I certify that I have reviewed the design and have approved its issue Accepted I have accepted the design for use by RailCorp
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Appendix 3
TMC 421
Design Investigation Form Date:___/___/____
Form 1 - Design Investigation. Site Investigation Form. (To be filled out during site investigation). 1
Location. (ie Track Region and kilometrage). ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________
2
Track structure to be drained. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________
3
Condition of existing drainage system (if any). ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________
4
Length of drainage system. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________
5
Restraints? – Inlet/outlet, existing adjacent structures, track curvature etc ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________
6
Estimate catchment area. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________
7
Site access. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________
8
Any specific site safety requirements. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________
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Conduct Services Search. Any visible services noted: ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________
10
Other comments. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________
11 12
Photographs: to be attached Site Sketch
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Appendix 4
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Calculation of Capacity Required Form
Form 2 - Calculation of Capacity Required.
a).
Location
_______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _____________________ (b)
Average Recurrence Interval (ARI)
(c)
Size of Catchment Area acting at section under investigation
(d)
ARI
= 50 (All RailCorp)
years
A
=
m2
Convert to km2 x10-6
=
km2
Critical Rainfall duration (tc) Method 1: the normal procedure is to calculate the equal area stream slope by graphing the catchment elevation, drawing a line between the start and finish of the catchment dividing equally the area above and below the line. For ease of calculations below it is assumed this is equivalent to the catchment slope. Mainstream Length (L).
L
=
km
change in height from start of catchment to point under consideration (h).
h
=
m
S =h/L
=
m/km
tc
=
mins
convert to hrs (/60)
=
hrs
tc
=
hrs
convert to mins (x60)
=
mins
Catchment Slope (S) tc = 58 L / (A 0.1 S 0.2) from AR&R (2001) book4 eq’n 1.3
Method 2: using the basic formulae (for Eastern New South Wales). tc = 0.76 A 0.38 (where A=km2) from AR&R (2001) book 4 eq’n 1.4
e).
Hydrology constants. These are looked up on contour style maps from AR&R Volume 2. 2
MAP 1.7 Æ 1hr duration, 2 year ARI
i 1hr
=
mm/hr
MAP 2.7 Æ 12hr duration, 2 year ARI
2
i 12hr
=
mm/hr
MAP 3.7 Æ 72hr duration, 2 year ARI
2
i 72hr
=
mm/hr
MAP 4.7 Æ 1hr duration, 50 year ARI
50
i 1hr
=
mm/hr
MAP 5.7 Æ 12hr duration, 50 year ARI
50
i 12hr
=
mm/hr
MAP 6.7 Æ 72hr duration, 50 year ARI
50
i 72hr
=
mm/hr
G
=
MAP 8 Æ Geographical factor F2
F2
=
MAP 9 Æ Geographical factor F50
F50
=
Figure 5.1 Æ Runoff coefficient for a 10 year ARI
C10
=
i 6min
=
MAP 7c Æ skewness factor G
Calculate 6min duration, 2 year ARI.
2
mm/hr
From AR&R (2001) book 2 formulae B(3.1). 2
i6m = F2 ( 2 i 1hr )0.9
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50
Calculate 6min duration, 50 year ARI.
i 6min
=
mm/hr
From AR&R (2001) book 2 formulae B(3.2). 50
i6m = F50 ( 50 i 1hr )0.6
(f)
Determine the critical rainfall intensity Icr,50 for the critical duration tc and an ARI of 50 years. Method 1: Graphical method. Plot the points in e) on a Log-Pearson Type III Interpolation diagram (see Diagram 2.2) and join lines between these 2-year and 50-year ARI’s. Refer to AR&R (2001) Volume 1,Book 2. Method 2: Adopt AR&R Formulas that interpolate between rainfall durations. Determine modified intensity values (I1hr,50, I12hr,50, I72hr,50) using skew lines at the bottom of the graph. Plot these values as well as 50i6m on the Duration Interpolation Diagram 2.1 and read off the critical 50 year intensity, Icr,50. Refer to Section A.3 of AR&R (2001) book 2. Method 3: Utilise computer software (eg “IFD” or “Drains”) by entering values from e).
(g)
=
C10
=
mm/hr
Determine the 50 year runoff co-efficient C50. C10 - from previous (e) Geographical zone. From Figure 1.2 AR&R (2001) book 4.
zone
= zone B (for Sydney Metro area)
Determine Frequency factor (FF50). Using Formulas or interpolating values given in Table 1.1 AR&R (2001) book 4.
FF50
=
C50
=
Calculate C50 = C10 FF50
(h)
Icr,50
Calculate the 50-year peak flow rate Q50 utilising the Rational Method. This represents the amount of water that will flow on a catchment for the critical 50-year storm. F
Conversion factor for formulae F = 0.278 if A is in km
= 0.278
2
Q50 = F C50 Icr,50 A
Q50
=
m3/s
from AR&R (2001) book4 eq’n 1.1 (i)
Determine the required drain capacity To calculate I use Figures 2.18, 2.19, 2.20, 2.21 and equations 2.3, 2.4, 2.7 and 2.8 in AR&R (1977). QR = runoff quantity collected = Q50
QR
=
m3/s
QS = subsurface water intercepted
QS
=
m3/s
QC = watering entering from another system (eg separate drainage line)
QC
=
m3/s
QPF
=
m3/s
QPF = QR + QS + QC =
Note: this procedure determines the amount of water passing at a single point based on the original catchment area. If multiple catchment areas are incorporated into a system, then this process should be repeated for each catchment. Because of the repetitive and time-consuming nature of this procedure, it is recommended that such method be entered into a spreadsheet, or computer program. Alternatively, hydrology software incorporating AR&R methods may be a cost-effective method to use in preference.
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Track Drainage
TMC 421
10 10
§:
0.0
0.0
0.1
0.1
O.l
0.2
UJ
0.3
1-
z
§: 1-
LU
0.·•
z 0.1 UJ
u:u.
0.5
M
(3
Q
LU
u.
u.
UJ
0
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STANDARD DEVIATE ( YK) fOR AVERAGE RECURRENCE INTERVAL Y YRS FOR LOG · Pe:ARSON TYPE ll[ DISTRIBUTION
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METEOROLOGY
LOG • PEARSON TYPE Ill INTERPOLATION DIAGRAM FOR STANDARD AVERAGE RECURRENCE INTERVALS (ARI)
© Rail Corporation Issued December 2009
UNCONTROLLED WHEN PRINTED
DIAGRAM 2.2
Page 76 of 82
Version 1.2
RailCorp Engineering Manual — Geotechnical
Track Drainage
TMC 421
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© Rail Corporation Issued December 2009
BUREAU OF
METEOROLOGY
DURATION INTERPOLATION DIAGRAM
UNCONTROLLED WHEN PRINTED
DIAGRAM 2.1
Page 77 of 82
Version 1.2
RailCorp Engineering Manual — Geotechnical Track Drainage
Appendix 5
© Rail Corporation Issued December 2009
TMC 421
Drawings: Typical Examples
UNCONTROLLED WHEN PRINTED
Page 78 of 82 Version 1.2
RailCorp Engineering Manual — Geotechnical
Track Drainage
TMC 421
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N/A
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UNCONTROLLED WHEN PRINTED
Page 79 of 82
Version 1.2
RailCorp Engineering Standard - Geotechnical
Appendix 6
ESC 420
Approved Track Drainage Products
Manufacturer ADS
Version: 2.0 Draft A Issue Date: May, 2009
Supplier
Type
Cubic Solutions High density polyethylene (HDPE)
© Rail Corporation 2009
Page 80 of 82
RailCorp Engineering Standard - Geotechnical
Version: 2.0 Draft A Issue Date: May, 2009
ESC 420
© Rail Corporation 2009
Page 81 of 82
RailCorp Engineering Standard - Geotechnical
Appendix 7
ESC 420
R Loading Configuration The ‘R’ vehicle is a rigid truck with the same configuration as the prime mover portion (first 3 axles) of the ‘T’ vehicle and the numerical portion is the vehicle’s weight in tonnes.
Standard
T44
Vehicle
4.9
9.8
9.8
9.8
Axle Loads (Tonnes)
1800
9.8
3700
1200
1200 Variable 3000-8000 To produce maximum loading effect
R20
Vehicle
Design Vehicle Configurations
Version: 2.0 Draft A Issue Date: May, 2009
© Rail Corporation 2009
Page 82 of 82
TRACK DRAINAGE
Version 1.2 Issued December 2009
Owner:
Principal Engineer Geotechnical
Approved by: John Stapleton Group Leader Standards Civil
Authorised by:
Jee Choudhury
Principal Engineer
Disclaimer This document was prepared for use on the RailCorp Network only. RailCorp makes no warranties, express or implied, that compliance with the contents of this document shall be sufficient to ensure safe systems or work or operation. It is the document user’s sole responsibility to ensure that the copy of the document it is viewing is the current version of the document as in use by RailCorp. RailCorp accepts no liability whatsoever in relation to the use of this document by any party, and RailCorp excludes any liability which arises in any manner by the use of this document. Copyright The information in this document is protected by Copyright and no part of this document may be reproduced, altered, stored or transmitted by any person without the prior consent of RailCorp
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Engineering Manual
TMC 421
RailCorp Engineering Manual — Geotechnical Track Drainage
TMC 421
Document control Revision
Date of Approval
Summary of change
1.2
December 2009
1.1
October 2007
C4.2.3.2: change to minimum pipe slope as per ESC 420; C4.6.1 Table 6: deleted details relating to drain slope of 1 in 300, Flowcharts 2 and 3 updated for change in minimum slope, Form 2 section (f): minor changes to wording; inclusion of Duration Interpolation Diagram 2.1.
1.0
October 2006
First issue as a RailCorp document. Replaces RTS 3432 and RTS 3433
Changes detailed in chapter revisions
Summary of changes from previous version Chapter
Current Revision
Control pages
1.1
Change of format for front page, change history and table of contents
1
1.1
Format change only
2
1.1
Format change only
3
1.1
Format change only
4
1.1
Format change; changes to be consistent with ESC 420 V2.0
5
1.1
Format change only
6
1.1
Format change only
7
1.1
Format change only
App 1
1.1
Format change only
App 2
1.1
Format change only
App 3
1.1
Format change only
App 4
1.1
Format change only
App 5
1.1
Format change only
App 6
1.1
New
App 7
1.1
New
© Rail Corporation Issued December 2009
Summary of change
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RailCorp Engineering Manual — Geotechnical
Track Drainage
TMC 421
Contents Chapter 1 C1-1 C1-2 C1-3 C1-4 Chapter 2 C2-1 C2-2 Chapter 3 C3-1 C3-2 C3-3 Chapter 4 C4-1 C4-2 C4-3 C4-4 C4-5 C4-6 C4-7 Chapter 5 C5-1 C5-2 C5-3 C5-4 C5-5 C5-6 C5-7 Chapter 6 C6-1 C6-2 C6-3 C6-4 C6-5 Chapter 7 C7-1 C7-2 C7-3 C7-4 C7-5
Introduction to Manual ............................................................................................................. 4
Purpose....................................................................................................................................... 4
How to read the Manual.............................................................................................................. 4
References.................................................................................................................................. 4
Definitions, abbreviations and acronyms .................................................................................... 4
General Requirements.............................................................................................................. 5
Introduction ................................................................................................................................. 5
Competencies ............................................................................................................................. 5
Types of Track Drainage .......................................................................................................... 6
Introduction ................................................................................................................................. 6
Surface Drainage ........................................................................................................................ 6
Subsurface Drainage .................................................................................................................. 8
Design of Track Drainage....................................................................................................... 17
Introduction ............................................................................................................................... 17
Design Criteria .......................................................................................................................... 17
Design Investigation.................................................................................................................. 23
Estimation of the Required Drainage System Capacity............................................................ 25
Surface Drain Design................................................................................................................ 27
Subsurface Drain Design .......................................................................................................... 33
Other Design Considerations.................................................................................................... 37
Construction of Track Drainage ............................................................................................ 38
Line and Grade ......................................................................................................................... 38
Site Preparation ........................................................................................................................ 39
Excavation................................................................................................................................. 39
Surface Drain Construction....................................................................................................... 40
Subsurface Drain Construction ................................................................................................. 40
Other Types of Construction ..................................................................................................... 44
Inlets and Outlets ...................................................................................................................... 44
Maintenance of Track Drainage............................................................................................. 46
General ..................................................................................................................................... 46
Surface Drainage ...................................................................................................................... 47
Subsurface Drainage ................................................................................................................ 49
Typical problems and solutions.................................................................................................50
Preparation for Flooding ........................................................................................................... 55
Documentation Requirements............................................................................................... 57
Introduction ............................................................................................................................... 57
Review Process ........................................................................................................................ 57
Drawing requirements............................................................................................................... 58
Hydrology/Hydraulic Report requirements................................................................................ 60
External party development discharging onto or through the rail corridor................................ 61
Appendix 1
Flow Charts.............................................................................................................................. 63
Appendix 2
Drainage Design Checklist..................................................................................................... 66
Appendix 3
Design Investigation Form..................................................................................................... 72
Appendix 4
Calculation of Capacity Required Form ............................................................................... 74
Appendix 5
Drawings: Typical Examples ................................................................................................. 78
Appendix 6
Approved Track Drainage Products ..................................................................................... 80
Appendix 7
R Loading Configuration........................................................................................................ 82
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TMC 421
Chapter 1 Introduction to Manual C1-1
Purpose The purpose of this manual is to provide a comprehensive guide for the design, construction and maintenance of effective track drainage. Regular examination, inspection and routine maintenance of drainage systems is essential in maintaining the integrity of the track formation, supporting embankments and cuttings. Neglect of drainage problems will inevitably lead to track problems. Inspection of track drainage is included in Track Engineering Manual TMC 203.
C1-2
How to read the Manual When you read this manual, you will not need to refer to RailCorp Engineering Standards. Any requirements from standards have been included in the sections of the manual and shown shaded. The shaded sections in this Manual are extracts from RailCorp Standard ESC 420 “Track Drainage”. Reference is however made to other Manuals.
C1-3
C1-4
References TMC 203
Installation & Maintenance Manual – Track Inspection
TMC 411
Earthworks Manual
AS 3706
Geotextiles – Methods of test
AS 3725
Loads on buried concrete pipes
AS 5100
Bridge design
Institution of Engineers Australia
Australian Rainfall & Runoff 2001
ED 0022P
RailCorp CAD & Drafting Manual – All Design Areas
ED 0026P
RailCorp CAD & Drafting Manual – Track
ED 0027P
RailCorp CAD & Drafting Manual – Bridges & Structures
CV 0400998
Ballast Cage (Lobster Pot) with Removable Lid
CV 0497068
Pipe Culverts Headwalls to Suit Pipes 225-600mm Diameter
CV 0497069
Pipe Culverts Headwalls to Suit Pipes 675-1800mm Diameter
Definitions, abbreviations and acronyms Cess drain:
located at formation level at the side of the track
Catch drain:
intercepts overland flow or run-off before it reaches the track and related structures such as cuttings or embankments
Mitre drain:
connected to cess and catch drains to remove water or to provide an escape for water from these drains
Multiple tracks:
more than 2 tracks
Track drainage:
drainage of the track formation including diversion of water away from cuttings and embankments
Site supervisor:
a qualified civil engineer or a competent person with delegated engineering authority for drainage construction.
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RailCorp Engineering Manual — Geotechnical Track Drainage
TMC 421
Chapter 2 General Requirements C2-1
Introduction This manual specifies the design, construction and maintenance requirements for track drainage systems. It covers drainage of the track formation, supporting embankments and cuttings. This manual does not cover drainage from platforms, buildings, overbridges, footbridges, airspace developments, external developments, access roads, roads outside the rail corridor, Council drains or properties adjacent to the rail corridor. Track drainage is to be designed to capture water flows calculated in accordance with this manual. No other drainage is to be discharged into the track drainage system without the approval of the Chief Engineer Civil.
C2-2
Competencies The design of track drainage shall only be undertaken by a suitably qualified engineer with competency in track drainage design and with delegated Engineering Authority for track drainage design. The construction of surface and subsurface drainage shall only be carried out under the supervision of a Site Supervisor.
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TMC 421
Chapter 3 Types of Track Drainage C3-1
Introduction Without adequate track drainage, track formation may become saturated leading to weakening and subsequent failure. Formation failure may be indicated by any of the following; mud pumping up through the ballast, repeated top and line problems, bog holes, or heaving of the formation. If the permanent way or track structure is to be maintained at a suitable standard for the passage of freight or high-speed passenger trains, adequate drainage must be installed in new or upgraded track, and existing drainage must be maintained so that it works effectively. Track drainage consists of two types:
C3-2
−
Surface drainage
−
Subsurface drainage.
Surface Drainage Surface drainage removes surface runoff before it enters the track structure, as well as collecting water percolating out of the track structure. Basic grading of the ground on either side of the track is a form of surface drainage, and allows water flowing out of the track structure to be removed. Shoulder grading may be used in very flat areas where it is difficult to get sufficient fall for either surface or subsurface drains. Shoulders graded to fall away from the track formation
Figure 1 Typical Track Formation There are three main types of surface drainage. These are:
−
Cess drains
−
Catch drains
−
Mitre drains.
Figure 2 Surface Drainage Types © Rail Corporation Issued December 2009
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C3-2.1
TMC 421
Cess Drains Cess drains are surface drains located at formation level at the side of tracks, to remove water that has percolated through the ballast and is flowing along the capping layer towards the outside of the track formation. Cess drains are primarily intended for the protection of the formation by keeping the formation dry. Cess drains are most frequently found in cuttings where water running off the formation cannot freely drain away. C
C
Cess drain
30
1
Figure 3 - Cess drain - Typical location Surface drains can be constructed on fairly flat grades, as they are easily cleared of any sediment that may collect in them.
C3-2.2
Catch Drains The purpose of catch drains (also known as top drains) is to intercept overland flow or runoff before it reaches the track. They reduce the possibility of causing damage to the track or related structures, such as cuttings or embankments. Catch drains are generally located on the uphill side of a cutting to catch water flowing down the hill and remove it prior to reaching the cutting. If this water was allowed to flow over the cutting face, it may cause excessive erosion and subsequent silting up of cess drains.
Figure 4 – Typical catch drains Catch drains may be used alongside tracks that cut across a slight downhill grade.
C3-2.3
Mitre Drains Mitre drains are connected to cess and catch drains to provide an escape for water from these drains. Mitre drains should be provided at regular intervals to remove water before it slows down and starts to deposit any sediment that it may be carrying.
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RailCorp Engineering Manual — Geotechnical Track Drainage
TMC 421
Figure 5 - Mitre drains
C3-3
Subsurface Drainage Subsurface drainage is necessary for maintaining the integrity of the track formation and ensuring
the stability of earth slopes.
Subsurface drainage is used for:
−
drainage of the track structure
−
controlling of ground water
−
the draining of slopes.
Subsurface drainage shall be provided in locations where the water table is at or near earthworks level.
Subsurface drainage shall be provided along the cess, between, across, or under tracks as
required.
Advice should be sought from the Principal Geotechnical Engineer before designing and installing
sub-surface drainage.
Subsurface drainage systems shall be designed to take surface runoff, ground water and seepage,
and water collected from other drainage systems to which the new system is being connected.
Most systems will only have to cater for surface runoff.
If a drainage system is required to remove ground water and seepage, a detailed hydrological and
geotechnical investigation is required to determine the volume of water for the sizing of drains.
The volume of water from other systems is determined from the outlet capacity of that system.
Subsurface drains are used where adequate surface drainage cannot be provided due to some
restriction or lack of available fall due to outlet restrictions. Locations where these circumstances
may occur are:
−
Platforms
−
Cuttings
−
Junctions
−
Multiple tracks
−
Bridges
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RailCorp Engineering Manual — Geotechnical Track Drainage
C3-3.1
TMC 421
Functions of Subsurface Drains Subsurface drainage systems perform the following functions: −
Collection of infiltration water that seeps into the formation (capping layer), as shown in Figure 6.
−
Draw-down or lowering of the watertable, as illustrated in Figure 7.
−
Interception or cut-off of water seepage along an impervious boundary, as illustrated in Figure 8.
−
Drainage of local seepage such as spring inflow, as shown in Figure 9.
Rainfall
C
1
30
Capping layer Collector drains
Figure 6 - Collection of water seeping into the ballast structure. Original ground level
C
Cutting slope Original watertable 30
Draw-down drain
1
Watertable
Draw-down drain
Figure 7 - Lowering the watertable.
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RailCorp Engineering Manual — Geotechnical Track Drainage
TMC 421
Geotextile Seepage Zone
Aggregate Filter Slotted Pipe
Type 1: Aggregate, geotextile and slotted pipe drain
Trench backfilled with excavated material
Geotextile drain Seepage Zone
Slotted Pipe Type 2: Geotextile drain
Figure 8 - Interception and cutoff of seepage water.
Cutting face
Connecting to either ditch or pipe drain Plan showing location of seepage drains
Geotextile Aggregate Slotted pipe Slotted pipe
Section A-A A C 20
1
A
Section A-A - Seepage drain
Figure 9 - Drainage of local seepage.
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RailCorp Engineering Manual — Geotechnical Track Drainage
C3-3.2
TMC 421
Types of Subsurface Drains Subsurface drains normally used for track drainage can be classified into three types according to
their location and geometry:
−
Longitudinal drain (Figure 10).
−
Transverse drain (Figure 11).
−
Drainage blankets (Figure 12).
Sump Cutting
A
Up track
A
Down track Longitudinal drain
Catch Drain
C
Capping layer Aggregate Geotextile Slotted pipe Section A-A
Figure 10 - Typical longitudinal drain arrangement. C
Geotextile if required Side of excavation
Compacted fill
Rock protection for pipe outlet Free draining rockfill
Slotted pipe
Figure 11 - Typical transverse drain.
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RailCorp Engineering Manual — Geotechnical Track Drainage
TMC 421
Geotextile
Drainage blanket Spall protection
Figure 12 - Typical drainage blanket. Two other types of subsurface drainage are: −
Horizontal drains (Figure 13).
−
Vertical drains (Figure 13).
Unstable soil
Excavation
Embankment Watertable Permeable blanket
Horizontal drain Vertical well drains
Figure 13 - Typical horizontal and vertical drain arrangement. Horizontal and vertical drains are more specialised and are seldom used for track drainage. Horizontal drains are generally used to drain wet soils and speed consolidation of earth structures. Vertical drains may also be used to speed consolidation. Another type of vertical drain is used to drain water from behind retaining walls or bridge abutments.
C3-3.3
Subsurface Drain Material Types Subsurface drains may also be classified according to the materials used in the drain. For example: −
Aggregate drains
−
Pipe drains
−
Geotextile drains
−
A combination of the above.
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RailCorp Engineering Manual — Geotechnical Track Drainage
C3-3.3.1
TMC 421
Aggregate Drains These drains consist of permeable granular material. The aggregate should be coarse enough to be free draining, but not so coarse as to allow the migration of fines into or through the permeable material. The graded aggregate is to be wrapped in a geotextile (Figure 14).
Graded aggregate
Subsoil
Geotextile filter
Figure 14 - Cross-section of an aggregate drain.
C3-3.3.2
Pipe Drains These consist of perforated or slotted pipes, installed by trenching and backfilling. Some type of filter material around the pipe or permeable backfill is normally required to minimise clogging of the drain perforations or slots (see Figures 15, 16 & 17).
Graded aggregate
Impervious Subsoil
Geotextile filter Slotted pipe
Figure 15 - Cross-section of a typical subsoil drain used in impervious soil (eg clayey soils) Geotextile overlap
Graded aggregate Geotextile filter
Pervious Subsoil
Slotted pipe
Figure 16 - Cross-section of a typical subsoil drain used in pervious soil (eg sandy soil).
Capping Impervious Subsoil Pervious fill Geotextile filter Slotted pipe
Figure 17 - Cross-section of a subsoil drain where the pipe is wrapped in geotextile. (Alternative slotted pipe system)
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RailCorp Engineering Manual — Geotechnical Track Drainage
C3-3.3.3
TMC 421
Geotextile Drains A geotextile drain may be a horizontal, vertical, or inclined blanket whose purpose is to collect subsurface water and convey it along the plain of the fabric to an outlet. The drain must also act as a filter to keep soil particles out of pores and prevent clogging. An example is shown in Figure 18. Vertical geotextile drain
Retaining wall
Horizontal geotextile drain (optional)
Backfill Collector pipe
Figure 18 - Geotextile drain behind a retaining wall. A similar arrangement may be used behind bridge abutments.
C3-3.3.4
Other Types of Subsurface Drain Where large volumes of water may need to be removed by subsurface drains, a carrier pipe may be used in conjunction with a collector drain, as shown in Figure 19. With this arrangement the collector drain does not need to carry all the water. The advantage of this arrangement is that excess (large volumes) water is removed from the collector drain thus preventing it seeping into the subgrade again at a point further down the drainage route. Figure 19 shows a typical arrangement for a collector drain and carrier pipe located between two tracks. The subsurface water is collected by the collector drain between the two sumps shown, it is then conveys water to the down stream sump where it can enter the carrier pipe and be removed without any risk of it re-entering the subgrade. See Figure 33 for an example of this system used in yard drainage.
Sump cage
Subsoil drain (collector)
Sump Sump Carrier pipe
Figure 19 - Subsoil collector drain plus a larger carrier pipe
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RailCorp Engineering Manual — Geotechnical Track Drainage
C3-3.4
TMC 421
Inlets and Outlets There are various types of inlets and outlets in use for subsurface drains. The main purpose of inlet and outlet protectors is to reduce erosion. Where outlet velocities are expected to be high, some form of energy dissipater should be installed. Also, where the sediment load of the water being discharged from a drainage system is high, a silt trap should be installed (see Figure 20 below). Rectangular Silt Trap collects deposited silt and is easily cleaned
Figure 20 - Typical silt trap installed in drains with high sediment loads. Some typical examples of inlet and outlet protection are:
−
Precast concrete units
−
Grouted sand bags (Figure 21)
−
Concrete (Figure 22)
−
Reno mattresses and gabions (Figure 23)
−
Revetment mattress (Figure 24)
−
Spalls grouted or hand packed (Figure 25)
Pipe outlet
Grouted sand bags
Figure 21 -Grouted Sand Walls.
Pipe outlet
Concrete headwall
Figure 22 - Concrete Headwall.
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RailCorp Engineering Manual — Geotechnical Track Drainage
TMC 421
Cut-off wall
Figure 23 - Gabion Headwall.
Wire basket headwall and mattress apron, Used mainly for larger pipe outlets
Figure 24 - Revetment Mattress.
A typical arrangement of hand packed walls. Cut-off wall should be provided at the bottom of the headwall to prevent the wall being scoured out and washed away, particularly on the down stream side.
Figure 25 - Spalls used as a Headwall.
NOTE: As mentioned in Figure 25, on the down stream side of the outlet, water getting under the headwall structure and causing scouring and the eventual washaway of the headwall is a problem that must not be overlooked. The best way to help prevent this occurring is to provide a cut-off wall at the end of the headwall (see Figure 23 for an example).
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RailCorp Engineering Manual — Geotechnical Track Drainage
TMC 421
Chapter 4 Design of Track Drainage C4-1
Introduction The purpose of this section is to specify design criteria and the design process to enable track and related structures to be drained effectively using either surface or subsurface drainage systems. Proper drainage design, using the design process detailed in this section, may allow problems to be discovered early and enable easier construction. Only staff with the appropriate RailCorp Engineering Authority shall carry out the design of track drainage. This section discusses the design process from the initial concept through to the detailing of the drain capacity and components required. Flow charts of the design process are provided in Appendix 1. A drainage design checklist is provided in Appendix 2.
C4-2
Design Criteria
C4-2.1
General Drainage systems are to be designed for the peak capacity calculated by the Rational Method. The Average Recurrence Interval (ARI) shall be 50 years. Proposed variations to the design ARI due to site constraints or other factors shall be supported by a risk assessment and shall be approved by the Chief Engineer Civil. The minimum design life of all track drainage components shall be 50 years with consideration given to site location and groundwater conditions. The following configurations are not approved for track drainage on the RailCorp network: −
plastic pipes: unplasticised polyvinylchloride (UPVC); polypropylene
−
inverted syphon systems.
Drainage cell systems shall only be used with the approval of the Principal Engineer Geotechnical.
C4-2.2
Surface Drainage
C4-2.2.1
Cess Drains The flow capacity of the open channel cess drain shall be greater than the peak flow rate. For ease of maintenance, over sized channels can be adopted to allow a certain degree of sediment build up to occur and still work effectively. Type 2 - Rectangular
Type 1 – Trapezoidal
A
B
C
B
A C
Figure 26 - Channel Types
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The minimum dimensions of an open channel shall be: A= 200, B= 200, C= 300. The minimum slope for an open channel is to be 1:200. The location of the open channel shall comply with the formation shoulder distance specified in ESC 410 “Earthworks and Formation”. Where track drainage is incorporated within existing track constraints (eg cuttings) and the shoulder distance cannot be achieved, open channels are to be an adequate distance from the track to prevent ballast spill into the channel area. In this case, the edge of the channel closest to the track shall be a minimum of 2800mm from the design track centre. This minimum edge distance shall be increased as required based on track configuration (rail size, sleeper type, ballast depth) and track curvature. The material forming the open channel shall to be capable of withstanding the maximum permissible design velocity. Table 4 in C4-5 nominates the maximum velocity values for varying lining types. If problems are encountered or an area is prone to erosion, then geotechnical advice should be sought. If fibre reinforced concrete is specified, synthetic fibres shall be used. With multiple tracks, drainage is to be provided by sumps and pipes in the ‘six-foot’ between each alternate track. All cess drainage systems must be designed to discharge to an approved watercourse or existing drainage system, and the approval of the appropriate authority must be obtained.
C4-2.2.2
Catch Drains Catch drains shall be provided on the uphill side of a cutting to divert water from the cutting face. Drains shall be 1000mm minimum from the face of the cutting.
Catch drains shall be provided on the uphill side of embankments to divert water from the embankment toe. Drains shall be 1000mm minimum from the toe of the embankment.
Catch drains may be either lined or unlined depending on the local soil conditions. Half round pipes or dish drains may be used instead of lined channels. The location of drains shall comply with the requirements of TMC 411 Earthworks Manual.
C4-2.2.3
Mitre Drains Where mitre drains are required, they shall be provided at regular centres with a drain located approximately every 100 metres maximum. They should be installed at the ends of cuttings. The minimum slope of mitre drains shall be 1 in 200. The ends of mitre drains shall be splayed to disperse water quickly and reduce scouring.
C4-2.3
Subsurface Drainage
C4-2.3.1
General Subsurface drains are used where adequate surface drainage cannot be provided due to some restriction or lack of available fall due to outlet restrictions. Subsurface drainage shall be provided in locations where the water table is at or near earthworks level. Subsurface drainage shall be provided along the cess, between, across, or under tracks as required.
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With double and multiple tracks, the requirement is that the water from one track shall not cross another track to get away. Drainage shall be provided by sumps and pipes in the ‘six-foot’ as required.
Advice should be sought from the Principal Geotechnical Engineer before designing and installing subsurface drainage.
Subsurface drainage systems shall be designed to take surface runoff, ground water and seepage, and water collected from other drainage systems to which the new system is being connected. Most systems will only have to cater for surface runoff. If a drainage system is required to remove ground water and seepage, a detailed hydrological and geotechnical investigation is required to determine the volume of water for the sizing of drains. The volume of water from other systems is determined from the outlet capacity of that system. Subsurface type drains generally consist of a combination of any one of the following:
C4-2.3.2
−
Pipes
−
Geotextile (or Geofabric)
−
Aggregate filter
−
Sumps, grates, and sump covers or cages.
−
Inlets and outlets
Pipes The capacity of the proposed drainage system shall be determined using the peak flow rate calculated by the Rational Method, with adjustment made for subsurface water and water collected from other systems. The peak flow velocity within the pipe shall be less than the manufacturer recommended maximum limits. Pipes larger than the design size may be adopted to reduce the likelihood of the system becoming blocked and also enable easier cleaning. The minimum pipe diameter shall be 225mm (for ease of maintenance cleaning). The slope of pipes shall be 1 in 100. Where this is not achievable, the pipe shall be laid at the maximum achievable slope. Slopes flatter than 1 in 200 require the approval of the Chief Engineer Civil. Depth of pipes under the track shall be 1600mm minimum from top of rail to top of pipe or pipe encasing. Depth of pipes running parallel to the track shall be 600mm minimum from the design cess level to top of pipe. At specific sites where it is not feasible to comply with these pipe depth requirements and achieve an effective drainage system design, the pipe depth may be reduced to: −
1200mm minimum from top of rail to top of pipe or pipe encasing for under track pipes;
−
300mm minimum from the design cess level or 1000mm from top of adjacent rail (whichever produces the lowest invert level) to top of pipe for pipes running parallel to the track.
Acceptable pipe materials are: −
reinforced concrete
−
fibre reinforced concrete
−
steel
−
products listed in Appendix 6.
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Approved proprietary products shall be designed and installed in accordance with the manufacturer’s specifications. Steel pipes shall be designed to mitigate the effects of electrolysis and stray track currents. Designs shall be in accordance with the requirements of RailCorp’s Chief Engineer Electrical Systems. Both slotted and unslotted pipes may be used depending on the system type and its means of collecting and carrying water. Slotted pipes are preferred, as these do not rely on surface flow between sumps to collect water. Slotted pipes and perforated pipes are not suitable for under track pipe work. Minimum strength requirements are detailed in Table 1. The strength of reinforced concrete and fibre reinforced concrete pipes shall be determined in accordance with AS 3725. Material
Type
Minimum strength class
Reinforced concrete
Slotted and unslotted
4
Fibre reinforced concrete
Slotted and unslotted
4
Steel
Slotted, perforated and unslotted
N/A
Table 1 Acceptable pipe types and minimum strength requirements
If railway live loads are applicable, then the pipes must be designed for train loads as follows:
Passenger Main Lines and Mixed Passenger Freight Main Lines
300-LA plus DLA
Light Passenger Main Lines
180-LA plus DLA
Heavy Freight Option
350-LA plus DLA
Sidings
300-LA plus 50% DLA Table 2 Railway Live Loads
NB. The ‘Reference Load’ is 300-LA. For the other loadings, all axles are to be proportioned by the ratio of the nominated LA load divided by 300. Operating Classes are defined in RailCorp standard ESC 200 “Track System”. For loadings less than 300 LA, future loading requirements need to be considered. Final approval of the design loads shall be obtained from the Chief Engineer, Civil. The Bridge Design Code, AS 5100.2, does not provide guidance on a suitable impact factor for railway loads distributed on fill. A dynamic load allowance (DLA) shall be adopted which varies linearly from 1.5 at 0.3m depth to 1.0 at 3.5m depth or greater (where the depth is measured from the top of rail).
Where slotted pipes are used, strength reductions for the slots shall be included in the design and shall be based on manufacturer’s recommendations.
Pipes located under sections of the rail corridor used for road vehicle access along the rail corridor, shall be designed for the R20 design load. See Appendix 7 for details of R loading configuration. Once the layout and required capacity of the drain has been established, it is necessary to detail the various items the will make up the system. This enables the correct components to be ordered quickly in the construction phase.
C4-2.3.3
Trench Excavation
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The width of trenches should only be as wide as necessary to ensure proper installation and compaction. The minimum trench width shall be pipe diameter plus 150mm on each side. For longitudinal drains located either within 2500mm of the track centre line or between tracks where track centres are less than 6000mm, the minimum trench width shall be pipe diameter plus 100mm on each side. Trenches shall be backfilled with suitable material and compacted to not less than 95% Relative Compaction as determined by AS.1289 Tests 5.1.1 and 5.3.1 (Standard Compaction).
C4-2.3.4
Pipe Bedding Type When determining the class of pipe to be specified in a sub-surface drainage system the bedding type assumed should be appropriate for what can be achieved during construction. Most under track drainage is constructed during track possessions where the more stringent requirements for placement and compaction of bedding material cannot always be achieved. For under track crossings that are to be constructed during a limited track possession, type “U” bedding in accordance with AS 3725 “Loads on buried concrete pipes” shall be used in design.
C4-2.3.5
Sumps, Ballast Cages and Covers Sumps are required as access points for surface water as well as for maintenance of the drainage system. Sumps shall be spaced at 30 to 50 metre centres, except through platforms where spacing shall be 20 to 30 metre centres. Reduced centres may be applicable in the 6-foot between tracks to account for track curvature. The minimum internal plan dimensions of a sump shall be 600mm x 600mm for depths greater than 1m. Minimum internal plan dimensions of 450mm x 450mm are acceptable for depths less than 1m.
Precast sumps with risers used to accommodate varying depths are to be adopted in preference to cast-in situ sumps.
All sumps are to be provided with a heavy-duty cast iron grate cover. In addition, all sumps within 2800mm of a track centre, or where site restraints dictate the possibility of ballast covering a pit, then a ballast cage (lobster pot) shall be provided. Refer to drawing CV 0400998 for details. Ballast cages shallbe of heavy-duty construction, capable of withstanding live loading from construction machinery. The cage shall be positioned to the outside edges of the sump. When installed the cages shall not extend above the top of sleeper level. Where the internal sump height (including risers) exceeds 1200mm, the following must be provided: −
Step rungs are to be provided at 300mm vertical centres. The step runs shall be located on the face looking at the oncoming train traffic (ie either Sydney face for the down track or Country face for up track).
−
Sump riser heights are to be selected such that step rungs do not come within 50mm of the top or bottom of the riser.
−
Where sumps are located in the 6-foot between tracks, the internal dimensions of the sump shall be increased to a minimum of 600mm wide (perpendicular to the tracks) x 900 mm to accommodate inspection access. The width shall be the maximum size available to enable proper placement of the sump and ballast cage (lobster pot) without clashing with the sleepers.
−
The internal dimensions of the sump in areas excluding the 6-foot, shall to be increased to a minimum of 900mm x 900mm to accommodate inspection access.
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Flushing Points Ground water and seepage drains shall have flushing points at appropriate intervals. Flushing points shall consist of “T” or “L” connections in the sub-surface pipe, with pipe connections extending to the surface for regular flushing with water to clear the sub-surface drain of fouling material.
C4-2.3.7
Aggregate Drains Aggregate drains are only suitable for use where small flow or seepage is expected. They are not to be used for the collection of surface water. The design of permeable drains may be carried out using Darcy’s equation. The permeability of clean gravel can range from 0.01 to 1.0 m/s. The aggregates used in aggregate drains are either 20mm nominal diameter or 53mm diameter (ballast), the permeability of these aggregates is: −
20 mm aggregate k = 0.15 m/s
−
53 mm aggregate k = 0.40 m/s
If in doubt as to the type of aggregate or the size of aggregate to use refer to RailCorp’s Geotechnical Engineer for advice. Aggregate drains are to be lined with a geotextile. A minimum 100mm layer of aggregate is to be placed on top of the geotextile to protect it from damage.
C4-2.3.8
Geotextiles The main purpose of a geotextile used in subsurface drainage is to act as a filter, which helps prevent silting-up of the drain it is protecting. The selected geotextile is to achieve the following characteristics: −
good permeability through the fabric material
−
good filtering qualities
−
resistance to clogging by particle fines
−
ability to stretch and conform to the shape of an open trench.
The selected geotextile is to exhibit the following mechanical properties as a minimum when tested in accordance with AS 3706: −
Tear Strength 400N
−
G Rating 2000
−
Grab Strength 1100N.
Geotextiles used in subsurface drainage must fully line the trench and have a minimum lap of 300mm at the top. The wrapped trench is to be covered by a minimum of 100mm of aggregate.
C4-2.3.9
Inlets and outlets There are various types of inlets and outlets in use. Some typical examples of inlets and outlets are: rip-rap, grouted rip-rap, sand bags, wire baskets (ie. gabions & reno matresses), revetment mattresses, precast concrete units and cast in place concrete. Example diagrams can be found in C3-3.4. To prevent soil erosion, all inlet/outlet points shall be provided with an appropriate size concrete headwall to suit the ground profile. Refer to drawings CV 0497068 and CV 0497069 for standard concrete headwalls.
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The ground covering at the pipe exit points shall be capable of withstanding the exit flow rates. Scour protection or energy dissipating devices may be required if existing ground cover cannot withstand the design rate. Where the sediment load of the water being discharged from a drainage system is high, a silt trap shall be included.
C4-3
Design Investigation
C4-3.1
Scope of investigation The main objective of a design investigation is to establish the requirements of the drainage system and any restrictions that may be imposed on the system. Aspects to be covered in the design investigation include: 1. Identification of the problem and thus the drainage objective. (i.e. what area is to be drained and for what reason). 2. Determination of the information required. (i.e. location, outside influences, fall available, possible outlets, access, site safety requirements, etc.) 3. Collection and study of all available existing/historical information. All available information from adjacent sites or the locality in general should be studied before embarking on any fieldwork. This will often save unnecessary fieldwork or may point out particular problems or aspects that should receive special attention. Included in this stage should be a full service search. This involves the check of the location of both RailCorp and public services. This may also involve site inspections with representatives from various bodies to accurately locate services, the position of which should then be marked, either on a plan or pegged. Other types of information that may be of use are, aerial photographs, maps (topographic, geological, soil, etc.), charts, meteorological and hydrological information). 4. Site inspection. A checklist should be prepared prior to the actual investigation so that the maximum amount of
information may be extracted from the site in a minimum time (see Form 1 in Appendix 3).
Items that should be looked at during a site inspection include:
∼
Access to and from the proposed site and any possible restrictions.
∼
Type and location of any existing drainage systems and any possible reasons for its
failure.
∼
The position and condition of any existing drainage outlets.
∼
Any other likely drainage outlets. Determine the outlet conditions and any likely restrictions because these may affect the design of the drainage system.
∼
Adjacent structures that may impact on the drainage design, or where the drainage design may cause instability to the structure.
5. Catchment area estimation: The catchment area for the drainage system needs to be estimated during the site inspection. This may be checked by comparison with maps of the area. A further inspection may be required at a later stage so that the area may be surveyed in order to establish the available fall and invert level for the inlet and outlet.
C4-3.2
Determination of the type of drainage system required On completion of the design investigation, information gathered shall be compiled and a decision made on the type of drainage system that is most suitable. The type of system chosen for each location is dependent on the site restraints, water source, track structure and long-term maintenance issues. The two types of drainage systems are surface and subsurface.
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If possible surface drains should be used in preference to subsurface drains since they are easily inspected and maintained. Note: care must be taken to ensure that the right drainage system is designed for each location. For example-using a slotted system to drain surface runoff that could have been collected by sumps. This could lead to a quicker failure of the system by allowing an easier route for water to pass (seep) into the formation.
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C4-4
Estimation of the Required Drainage System Capacity
C4-4.1
General At this point, the site requirements and restrictions, the drainage type, and the layout of the proposed drainage system should be known. The next step is to estimate the quantity of water that the drain will need to carry, so that the size of the drain and its various components may be determined. The quantity of water (QPF) that the drain is required to carry generally consists of: QPF = QR + QS + QC…………………………………………………………..(1) Where; QPF =
water quantity (m3/s or l/s)
QR =
runoff quantity collected (m3/s or l/s).
QS =
subsurface water quantity intercepted (m3/s or l/s)
QC =
collected water quantity from a drain of a connecting system (m3/s or l/s).
The calculated quantity (QPF) represents the peak flow that the drain will be required to carry, for a short time only. The quantity (QR) is calculated for the catchment size and critical rainfall duration by using the Rational Method. The value of intercepted subsurface water "QS" is difficult to determine. If a drainage system is required to remove intercepted subsurface water, a detailed hydrological/geotechnical investigation is usually required.
The volume of water conducted from other systems, "QC", is estimated from the outlet capacity of the system to which the new system is being connected. Provided the catchment area, drain size and slope are known (or can be measured), the maximum value of "QC" can be determined using the Rational Method. This information may also be available from the authority owning the asset (eg council). If the connecting system is a complex network of drainage a detailed study may be required. Account shall be taken of all water flowing onto the rail corridor from adjoining properties and streets.
C4-4.2
Average Recurrence Interval (ARI) In order to use the Rational Method it is necessary to adopt a relevant average recurrence interval (ARI). This is an approximate estimate of how often a particular event will occur on average. For example, an ARI of 1 in 50 years means that a particular storm event is likely to occur on average only once in every fifty years. If any modification to the ARI is desired, then a risk assessment shall be carried out to consider all impacts of such modification. Any modification to the ARI will need a waiver from RailCorp’s Chief Engineer Civil. Once the ARI is established the volume of water that the drain will carry can be calculated.
C4-4.3
The Rational Method The Rational Method provides a method for calculating the peak rate of discharge of a storm event for a specific ARI.
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If incorporating computer modelling in the design process, then a range of storm events representing varying rainfall duration shall be investigated. The drainage design shall be carried out adopting the critical rainfall event. Hydrology and hydraulic computer packages can be utilised for the design of track drainage. The following procedure deals with hand calculation methods only. The Rational Method is detailed fully in Australian Rainfall and Runoff (AR&R) published by the Institution of Engineers, Australia. The AR&R publication recommends the following steps for flow rate determination for sites in eastern New South Wales. Form 2 in Appendix 4 breaks down these steps and can be used as a calculation sheet. 1. Calculate the critical rainfall duration (tC) for the area under investigation Two methods may be adopted to calculate the critical rainfall duration. These methods are: i. ii.
Equal area stream slope’ – recommended for hilly or undulating sites as it gives a more realistic flow response time (refer to AR&R for this procedure). Basic formulae (for Eastern New South Wales) tC=0.76 A
0.38
…………………………………….…………………..(2) Where; tC = critical rainfall duration (in hours) A = catchment area (km2)
The catchment areas required for peak flow rate calculations shall be determined using (in order of preference) site survey, site measurements or suitably scaled topographic maps. 2. Calculate the critical 50 year design rainfall intensity (Icr,50). This step comprises of looking up a series of basic rainfall intensities, skewness factors and geographical factors from contour style maps found in Volume 2 of the AR&R guide. These values can be plotted on a log-Pearson Type III diagram (LPIII) or incorporated in interpolation formulas found in Book 2 of AR&R volume 1. From either of these two methods the 50 year design rainfall intensity ‘Icr,50’ for the critical duration tC can be determined. 3. Determine the 50 year runoff coefficient (C50) for the geographical area by determining the following: iii. Read the 10 year runoff coefficient value (C10) from Figure 1.1 in Volume 2 of the AR&R iv. Geographical zone B is adopted from Figure 1.2 (AR&R) – for Sydney Metropolitan Area. v. Interpolate or calculate the 50-year frequency factor FF50 from Table 1.1 (AR&R) based on site elevation. vi.
Calculate C50 = C10xFF50 (no units)
4. Calculate the 50 year peak flow rate (Q50). Adopt the Rational Method formula. Q50 = F×C50×Icr,50×A………………………………….…………………..(3) Where; Q50 =
peak flow rate (m3/s) for ARI =50 years
F=
conversion factor to balance units used. = 0.278 if A is in km2 = 0.000278 if A is in hectares (ha).
C50 =
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I cr,50=
average rainfall intensity (mm/hr) for the critical duration
A=
catchment area (km2 or ha).
The peak flow rate is utilised in determining how much water is likely to rain onto a catchment and thus enabling the sizing of the drainage system under consideration.
C4-5
Surface Drain Design The following steps can be used to correctly determine the required size of surface drainage: Step A: Determine the required channel capacity Prior to estimating the size of a surface drain the required capacity must either be known or calculated using Equation 1. QPF = QR + QS + QC…………………………………………………………..(1) For surface drains " QS " and " QC " can usually be neglected. In this case, Equation 1 becomes QPF = QR = Peak flow rate (m3/s). Example 1: A rainfall runoff quantity of 0.15m3/s was calculated to act on a catchment for the 50-year ARI critical duration storm (from the “Rational method”). There is no subsurface water intercepted, but a nearby stormwater pipeline enters the channel and adds 0.07 m3/s. What is the total water quantity the channel will need to be designed for? Solution 1: The design flow capacity can be determined from Equation (1)
QPF = QR + QS + QC = 0.15 + 0 + 0.07 = 0.22 m3/s
The channel will need to be sized to take a 0.22m3/s flow rate or greater.
Step B: Select a Mannings roughness coefficient A value of the roughness coefficient 'n" must then be selected from Table 3. Channel Material
Roughness Coefficient ‘n’
Closed Conduits concrete pipe or box
0.012
corrugated steel pipe - helical
0.020
vitrified clay pipe
0.012
fibre cement pipe
0.010
P.V.C. pipe
0.009
steel pipe
0.009 - 0.011
Lined open channels concrete lining
0.013 - 0.017
gravel bottom concrete sides
0.017 - 0.020
gravel bottom rip rap sides
0.023 - 0.033
asphalt rough
0.016
asphalt smooth
0.013
Unlined channels - Earth uniform section
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clean channel
0.016 - 0.018
with short grass
0.022 - 0.027
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Channel Material gravelly soil
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Roughness Coefficient ‘n’ 0.022 - 0.025
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Channel Material
Roughness Coefficient ‘n’
Unlined channels - Earth fairly uniform section no vegetation
0.022 - 0.025
grass plus some weeds
0.030 - 0.035
dense weeds
0.030 - 0.035
clean sides gravel bottom
0.025 - 0.030
clean sides cobble bottom
0.030 - 0.040
Rock smooth and uniform
0.035 - 0.040
jagged and irregular
0.040 - 0.045
Table 3: Value for Manning's roughness co-efficient "n" for different pipe & channel types. Step C: Determine the slope of the drain The minimum slope of a drain is 1 in 200 (i.e. 1 metre fall vertically for every 200 metres horizontally), though a minimum slope of 1 in 100 is preferred for self-cleaning purposes. It should be noted that as the slope of the drain becomes flatter, the tendency for a drain to become blocked due to sediment build-up increases. Consequently the maintenance of the drain also increases. Step D: Select a trial channel size Using the value of slope "S" and the roughness coefficient "n" selected previously, the capacity of the trial drain can be calculated using Equation 4 (Manning's equation) or a simplified version (Equation 5).
Q=
1 × A × R0.67 × S0.5 n ………………………………………..………(4)
Where; Q=
flow rate or capacity (m3/s)
n=
roughness co-efficient. From Table 3
A=
channel cross-sectional area
R=
hydraulic radius - examples given in Table 4
R=
A/P where P = wetted perimeter (i.e. the surface in contact with the water)
S=
slope of the drain.
If X = A x R0.67 Equation 4 becomes:
Q=
1 × X × S0.5 n ………………………………………….. (5)
See Table 4 for values of "X" for various channels:
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Channel Types: Type 1 - Trapezoidal
Type 2 - Rectangular
A B
C
B
Channel Dimensions (mm) No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
A 200 200 200 200 200 300 300 300 450 300 300 300 300 300 450 300 300 300 450 300 450 450 450 300 450 450 450 600 600
A
B 200 300 200 200 300 200 450 300 200 450 300 450 200 300 300 450 300 450 450 300 450 600 600
C 300 450 300 300 450 450 300 300 450 450 300 450 600 450 600 600 600 900 450 900 900 450 600 900 600 900 900 600 900
C Area (m2)
Wetted perimeter (m)
Hydraulic radius (m)
“X” (Eqn 5)
0.060 0.090 0.100 0.120 0.130 0.135 0.150 0.180 0.203 0.195 0.225 0.225 0.240 0.270 0.270 0.270 0.315 0.330 0.338 0.360 0.405 0.405 0.405 0.405 0.473 0.540 0.608 0.720 0.900
0.700 0.850 0.860 1.021 1.016 1.050 1.021 1.149 1.350 1.171 1.382 1.299 1.321 1.532 1.500 1.449 1.682 1.621 1.532 1.749 1.800 1.723 1.682 1.441 1.873 1.982 2.173 2.297 2.597
0.086 0.106 0.115 0.118 0.128 0.129 0.147 0.157 0.150 0.167 0.163 0.173 0.182 0.176 0.180 0.186 0.187 0.204 0.220 0.206 0.225 0.235 0.241 0.281 0.252 0.272 0.280 0.313 0.347
0.012 0.020 0.024 0.029 0.033 0.034 0.042 0.052 0.057 0.059 0.067 0.070 0.077 0.085 0.086 0.088 0.103 0.114 0.123 0.125 0.150 0.154 0.157 0.174 0.188 0.227 0.260 0.332 0.440
Table 4: Calculation of “X” for various channel sizes. Note: Smaller channels tend to become blocked with built up sediment very quickly.
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The following are typical examples of calculations to determine the capacity of an open channel. Example 2: For a trapezoidal channel (shown below) with a slope of 1 in 200 and a roughness coefficient "n" of 0.030. Calculate the channel capacity using a) equation 4 and b) equation 5 and Table 4:
300 450
600
450
Solution 2a) - using Equation 4 S = 1 in 200 = 0.005 n = 0.030 A = (600 × 300) + 2 × (0.5 × 300 × 450) A = 315,000 mm2 A = 0.315 m2 R = A/P
P = 2 × (300) × 2 + (450) × 2 + 600 P = 1682 mm
P = 1.682 m
R = 0.315/1.682
R = 0.187 m
Q=
1 × A × R0.67 × S0.5 n
Q=
1
× 0.315 × (0.187)0.67 × (0.005)0.5 0.03
Q = 0.243 (m3/s)
Solution 2b) - using Equation 5 and Table 4. S = 0. 005
n = 0.030
From Table 4, X = 0.103
Equation 4
Q=
1
× X × S0.5 n
Q=
1 × (0.103) × (0.005)0.5 0.03
Q = 0.243 (m3/s)
Step E: Check channel capacities Once the capacity of the trial drain is determined “Q” it must be compared with the required capacity found using Equation 1 “QPF”. If the capacity of the trial drain “QPF” is considerably greater or lesser than the required capacity “Q”, then a new trial drain should be selected and steps (c) and (d) repeated until the trial capacity is approximately equal to or slightly greater than the required capacity.
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Example 3: Check that the channel in Example 2 has is sufficient capacity to cater for the design storm as calculated in Example 1. Solution 3: The channel capacity “Q” of 0.243m3/s (Example 2) is greater than the design storm flow rate “QPF”of 0.220m3/s (Example 1). Therefore it has sufficient capacity. Step F: Calculate water velocities Once the required capacity is obtained, the flow velocity of water within the channel may be calculated. The velocity is calculated using Equation 6 as shown below: V=Q/A………………………………………………………………..(6) Where: V=
velocity (m/s)
Q=
flow rate (m3/s) calculated using Equation 1
A=
area of selected channel (m2)
Example 4: Calculate the flow velocity of water within the channel in Example 2. Solution 4: Q=0.22m3/s
A=0.315 m2 (from example 1-assumed flowing full)
V = Q/A = 0.220/0.315 = 0.69 m/s
Step G: Check channel lining In some cases it may only be possible to install a small drain and the flow through this drain may have a velocity greater than the maximum permissible velocity and consequently the channel must be lined. Table 5 gives the maximum permissible velocity of varying ground coverings. Channel Type Fine sand Silt loam Fine gravel Stiff clay Coarse gravel Shale, hardpan Grass Covered Stones Asphalt Boulders Concrete
Velocity (m/s) 0.45 0.60 0.75 0.90 1.20 1.50 1.8 2.5 3.0 5.0 6.0
Table 5: Maximum permissible velocities for various types of channel lining. Lining a channel changes the roughness coefficient "n"', and thus the capacity of the channel may be altered either up or down (See Table 3). A lining is selected such that the allowable velocity for the type of lining is greater than that calculated in step F, this is used as a first trial value.
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Example 5: The channel in example 4 is lined with grass covering. Is it sufficient to withstand the flow velocity. Solution 5: Velocity of water in channel = 0.69m/s (solution 4)
The maximum permissible velocity of grass lining = 1.8m/s (Table 5).
Therefore, grass has the required resistance and the lining is sufficient.
Step H: Completion If the capacity of the channel is inadequate or the ground cover velocity insufficient then modifying the channel size, slope or lining type will need to be done until all aspects are satisfactory. Complete Example
Example 6:
Calculate the required Channel size and lining type given that the required capacity of the 3 channel is 0.40 m /s. The existing soil is clay. Solution 6: Trial 1:
Step A: No subsurface water or connecting system. So QPF =0.40m3/s
Step B: n=0.016 (Table 3)
Step C: Adopt S=0.01 (desirable minimum slope)
Step D: Select Channel No. 14 from Table 4. A = 0.270 m2. X = 0.085
Q=
1 × X × S0.5 n = (1/0.016)x(0.085)x(0.01)0.5 = 0.53m3/s (Eq’n 5)
Step E: Channel capacity 0.53 m3/s> design capacity 0.40m3/s. ok Step F: V = Q/A = 0.40/0.270= 1.48m/s (Equation 6) Step G: Clay has permissible velocity capacity of 0.9m/s (Table 5) which is less than the design flow of 1.48m/s. Could modify size or change lining. Opt for a change of lining type to grass covered (capacity 1.8m/s). Step H: Must redo calculations, as n will change Trial 2: Try lining with higher permissible velocity – say grass lining Steps A, B & C: QPF =0.40m3/s. n=0.024 (Table 4). S=0.01 Step D: Same Channel No. 14 from Table 4. A = 0.270 m2. X = 0.085 Q= (1/0.024)x(0.085)x(0.01)0.5 = 0.35m3/s (Equation 5) <0.4m3/s therefore no good. Could modify size or change lining. Trial 3: Try smoother lining, with high permissible velocity - say asphalt Steps A, B & C: QPF =0.40m3/s. n=0.013 (Table 4). S=0.01 Step D: Same Channel No. 14 from Table 4. A = 0.270 m2. X = 0.085 Q= (1/0.013)x(0.085)x(0.01)0.5 = 0.65m3/s (Equation 5) Step E: Channel capacity 0.65 m3/s> design capacity 0.40m3/s. ok Step F: V = Q/A = 0.40/0.270= 1.48m/s (Equation 6)
Step G: Asphalt has capacity of 3.0m/s (Table 5) which is greater than the design flow of
1.48m/s. Therefore it is satisfactory.
Step H: Channel No 14 laid in bitumen at a 1% slope is satisfactory.
C4-6
Subsurface Drain Design
C4-6.1
Pipe Drains
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The following steps can be used to correctly determine the required size of subsurface drainage pipes: Step A: Determine the required pipe capacity Prior to estimating the size of a subsurface drain the required capacity must either be known or
calculated using Equation 1.
QPF = QR + QS + QC …………………………………………………………..(1)
Refer to Section 4.5 for more detail.
Step B: Select the pipe type The pipe type selected should be adopted based on the suitability of the system to the site. Unslotted pipes must be used for undertrack pipes whereas either slotted or unslotted pipes can be used elsewhere. Acceptable pipe materials by type are detailed in Table 1. Step C: Adopt a Mannings roughness coefficient A value for pipe roughness “n” can be obtained from the manufacturer for the product being adopted. Table 3 details typical values that are also acceptable. Step D: Determine the slope of the pipe The pipe slope may be determined from the geometry of the site to best suit site constraints. However, the minimum pipe slope is 1 in 300, (although a slope of 1 in 100 is preferable for selfcleaning purposes). The steeper the slope the lesser the maintenance requirements). Step E: Select a pipe size A trial pipe size can be found using Table 6 by selecting a pipe where “Q” is greater than the peak flow required “QPF”. Alternatively, The capacity of the pipe can be found by using Mannings Equation (Equation 4). Pipe Dia.
Pipe Material
225
F.C.
1 in 100 200
Max Flow Q (l/s) 58.3 41.2
225
Concrete
1 in 100 200
300
F.C.
300
450
F.C.
1 in 100 200
Max Flow Q (l/s) 370.3 261.8
53. 0 37.4
450
Steel
1 in 100 200
264.5 187.0
1 in 100 200
125.6 88.8
450
Concrete
1 in 100 200
336.6 238.0
Steel
1 in 100 200
104.6 74.0
525
F.C
1 in 100 200
558.7 395.0
300
Concrete
1 in 100 200
114.1 80.7
525
Concrete
1 in 100 200
507.9 359.1
375
F.C.
1 in 100 200
227.7 161.0
600
F.C.
1 in 100 200
797.7 564.0
375
Steel
1 in 100 200
175.1 123.8
600
Steel
1 in 100 200
498.5 352.5
375
Concrete
1 in 100 200
207.0 146.6
600
Concrete
1 in 100 200
725.1 512.7
Drain Slope
Pipe Dia.
Pipe Material
Drain Slope
Table 6 Capacities for various pipe types and sizes. L Notes to Table 6 1. FC = fibre cement pipe
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Steel = corrugated steel pipe Concrete = concrete or vitrified clay pipe PVC pipes are not to be used for track drainage design. They are included in Table 6 for assessment of existing pipe systems. To convert m3/s to l/s multiply by 1000 (ie 1000 litres = 1 cubic metre) The values of Mannings' roughness co-efficient used in the calculations for the values given in table 5 are as follows:
5. 6.
Concrete
n = 0.011
Fibre Cement
n = 0.010
P.V.C.
n = 0.009
Steel
100 - 300 dia
n = 0.012
375 dia
n = 0.013
450 dia
n = 0.014
600 dia
n= 0.015
Step F: Check the flow rates within the pipe Utilising Equation 5 (V=Q/A), the velocity of flow within the pipe can be determined. The flow velocity within the pipe shall be at an acceptable level so as not to cause damage to the pipe surface. The manufacturer has recommended maximum limits. Step G: Determine the strength of the pipe (pipe class) The pipe must be checked to see if it is suitable for the design and construction loads that are imposed on it. The method of calculation of pipe strength is to follow the relevant Australian Standard (eg AS 3725 – Loads on buried concrete pipes). If pipes are within a 45-degree projection of the outside of the sleeper (in any direction), then railway loading must be included. Dynamic loads must also be applied – Refer to section 4-2.3. If pipes are situated within a 45-degree projection of the outside of an access road (in any direction) then the loads applicable to the access vehicle must be included. Dynamic loads must also be applied – Refer to section 4-2.3. Pipe strength is also highly dependent on the type of trench excavation, fill material and compaction technique. When determining the class of pipe to be specified in a drainage system, type “U” bedding should be assumed, even if better bedding is specified on the drawings. Most track drainage is constructed during track possessions where the specified placement and compaction of bedding material cannot always be achieved. Where slotted pipes are used, strength reductions for the slots shall be included in the design and shall be based on manufacturer’s recommendations. Manufacturer supplied computer software is acceptable for this purpose of pipe strength design, provided it is in accordance with AS 3725. Minimum strength requirements are detailed in Table 1. Complete Example: Example 7: 3 A rainfall runoff quantity of 0.10m /s was calculated to act on a catchment for the 50-year ARI critical duration storm (from the rational method). There is no subsurface water intercepted, but a nearby stormwater pipeline enters the system and adds 0.02m3/s. What size reinforced concrete pipe is required to satisfy flow requirements?
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QPF = QR + QS + QC = 0.10 + 0 + 0.02 = 0.12 m3/s Step B: Reinforced concrete (given) Step C: Roughness n=0.011 (from Table 6 – notes) Step D: Pipe slope 1 in 200 (given) Step E: From table 6, a 375mm diameter RC pipe has capacity of 146.6l/s (0.146m3/s) which is greater than the design flow capacity. Also, the size is greater than the 225mm minimum. Step F: Flow rate within the pipe V=Q/A = 0.12/(3.142x0.375x0.375/4) = 1.1m/s which is less than the acceptable limit for concrete (6m/s). Therefore ok.
C4-6.2
Aggregate drains Aggregate drains are only suitable for use where small flow or seepage is expected. If a larger flow is expected a slotted pipe should be added to the system, and then the drain should be sized as described previously. A typical example of an aggregate drain is a blanket drain. Another type of aggregate drain is a French drain. Aggregate drains are to be lined with a geotextile. The capacity of an aggregate drain may be determined using Darcy's equation (Equation 7). Q = k × i × A ……………………………………………..……………….(7) Where: 3 Q = flow (m /s)
k = permeability of the aggregate i = hydraulic gradient or slope. A = cross sectional area (m2) The permeability of clean gravel can range from 0.01 to 1.0 m/s. The aggregates used in aggregate
drains are either 20 mm nominal diameter or 53 mm diameter (ballast), the permeability of these
aggregates is:
20 mm aggregate k = 0.15 m/s
53 mm aggregate k = 0.40 m/s
Equation 7 may be simplified if K = k × i, and Equation 8 becomes:
Q = K × A …………………………………………………………………(8)
Table 7 below gives values for "K" for use in Equation 8 in order to determine the capacity of
aggregate drains:
Slope
K = k × i (m/s) 20 mm
53 mm
1 in 100
0.00150
0.0040
1 in 200
0.00075
0.0020
1 in 300
0.00050
0.0013
1 in 400
0.00038
0.0010
1 in 500
0.00030
0.0008
Table 7 Values of K = k.i for various slopes.
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Example 8: If Q = 0.01 m3/s or 10 l/s an aggregate drain using 20 mm aggregate at a slope of 1 in 200, what size drain is required? Solution 8: Q=K × A this may be rearranged to: A = Q/K Therefore: A = 0.01/ 0.00075 A = 13.3 m2 For the same flow using 53 mm aggregate at a slope of 1 in 200, the area required is: A = 0.01 / 0.002 A = 5.0 m2
C4-7
Other Design Considerations When selecting a pipe, the type of environment must also be considered (i.e. is the water abrasive, acidic or alkaline). The manufacturer’s specifications should be consulted regarding the pipe’s suitability to various environments. Sizing of surface and subsurface drainage should consider maintenance implications. Using oversized channels may reduce sediment build-up and reduce maintenance. Adopting larger pipes may be beneficial fro access and cleaning requirements. The possible effects of non standard ballast profiles shall be considered. Geometry effects of laying longitudinal pipes adjacent track around curves shall be considered (eg may require reduced sump centres). The permanent effects of the drainage system located alongside existing structures (eg OHWS, retaining walls, platforms, embankments etc) shall be taken into account. The possibility of causing instability of an existing structure during the excavation stage must also be highlighted and accounted for. Conflict with existing services shall be included. Service searches shall be conducted and the locations of these services indicated on the design documentation.
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Chapter 5 Construction of Track Drainage This section deals briefly with the various forms of drainage construction. One important consideration is that each and every site must be assessed on its own merits. No two sites are ever exactly the same. This must be taken into account when selecting the site protection, equipment, and personnel required for each particular site. This section discusses the various steps involved in the construction of both surface and subsurface drainage systems.
C5-1
Line and Grade The line and grade of the drainage system, be it surface or subsurface, may be set out by one or a combination of the following methods: 1. Stakes, spikes, shiners (small reflective metal discs), marks or crosses set at the surface on an offset from the desired centre line. 2. Stakes set in the trench bottom on the pipeline as the rough grade for the pipe is completed. 3. Elevations given for the finished trench grade and pipe invert while laying the pipe or excavating the trench is in progress. Of these three methods, method (1) is the most commonly used for track drainage. Method (1) involves stakes, spikes, shiners, or crosses being set on the opposite side of the trench from where the excavated material is to be cast at a uniform offset, in so far as practicable, from the drain’s centreline. A table known as a cut sheet is prepared. This is a tabulation of the reference points giving the offset and vertical distance from the reference point to either: the trench bottom, the pipe invert or both. When laying the pipe it may be more practical to give two vertical distances, one to the trench bottom (excavation depth) and one to the top of the pipe, which is generally easier to measure to than the pipe invert. The grade and line may be transferred to the bottom of the trench by using batter boards, a tape and level, or patented bar tape and plumb bob unit. This method may be adapted to suit. For example it is common practice to have the proposed route surveyed with the reference points marked on the datum rail (either the Down rail or the low rail on a curve). The offset and vertical height may be easily transferred from the rail by use of a straight edge, spirit level and tape (see Figure 27 below).
Spirit level Straight edge
Measure depth from underside of straight edge to bottom of trench
Ballast
Sub soil
Trench
Figure 27 - Method of measuring the depth of a trench and offset to pipe centreline. If the track is on a constant grade that is suitable for the pipeline and trench, this grade may be adopted. This gives a constant vertical depth from the datum rail to the trench bottom and pipeline, making construction and grade control much easier. © Rail Corporation Issued December 2009
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Another method of controlling the line and grade is the use of lasers. A laser beam is passed through the centre of the pipeline at the desired grade. It strikes opaque targets attached to the end of the pipe, and the pipe may then be either lifted/packed or lowered until the laser passes through the centre of the target.
C5-2
Site Preparation The amount of preparation varies from site to site. Operations that should be classified as site
preparation are:
−
clearing;
−
removal of unsuitable soils;
−
preparation of access roads;
−
detours and bypasses;
−
improvements to and modification of existing drainage;
−
location, and protection or relocation of existing utilities.
The success of the construction phase depends to a great degree on the thoroughness of the
planning and the execution of the site preparation work.
C5-3
Excavation With favourable ground conditions, excavation can be accomplished in one simple operation. Under more adverse conditions it may require several steps, such as; clearing, rock breaking, ripping or blasting and excavation. When excavating for a pipeline the trench at and below the top of the pipe should be wide enough to ensure adequate compaction on the sides of the pipe can be achieved. The minimum width on either side of the pipe shall be in accordance with C4.2.3.3. The amount of excavation and the types of equipment required may vary, so each site must be assessed on its merits to determine the type and quantity of equipment necessary. Excavation in the vicinity of structures shall comply with the requirements of TMC 411 Earthworks Manual. Particular conditions that should be taken into account when selecting equipment are: −
Site access
−
Size and amount of excavation necessary
−
Site conditions i.e. firm or boggy ground conditions
−
Location and availability of plant
−
Whether the plant item required has to be floated to the site. (If so the offloading conditions and a suitable area should be checked).
−
Services in the area.
Typical items of plant (equipment) utilised are:
−
Gradall (normal or highrail)
−
Backhoe
−
Tiltable dozers
−
Graders
−
Front end loaders
−
Tracked excavators
−
Hydraulic excavators
−
Bogie tippers and 4wd dumpers, etc.
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C5-4
Surface Drain Construction
C5-4.1
Requirements The main purpose of surface drains is to remove surface water from near the tracks and disperse it as quickly as possible. To do this, the drainage trench or ditch should be constructed at a uniform even grade, with no low sections where water may pond and seep into track formation, thus defeating the purpose of the drainage system. The grade of the drainage trench should be a minimum of 1 in 200 where practicable. Flatter grades may be used but require more regular inspection and maintenance, since they tend to become blocked with sediment more quickly than drains with steeper grades. Where the velocity of the water is greater than that shown in Table 5 in C4-5, some form of scour protection is required eg. lining the channel. Where doubts exist as to the erodability of a soil, RailCorp’s Geotechnical Engineer should be consulted. Where any surfaces are cleared of vegetation, these areas must be re-vegetated at the end of construction, to prevent unnecessary build-up of silt in nearby drains.
C5-4.2
Construction Steps −
Survey the proposed drainage route. This may be carried out during the preliminary investigation.
−
Establish and mark out reference points for use during construction. Marking out may consist of paint marks on the datum rail or star pickets. The interval used for the reference marks depends on the length of the drainage system. For example, for a short drain the interval may be 5.0 metres.
−
Clear the site. This should be part of any site preparation work carried out. This may involve relocation of signal troughing, clearing vegetation, etc.
−
Excavate to required level. When excavating the trench, use a bucket width equal to the width of the trench base, then add a batter to the sides of the trench formed. Monitor excavation with the method described in Section 5.1. Once the trench has been constructed, level and compact the trench base making sure that no low points exist.
−
Check for risk of erosion. If this is expected to be high the drain may require lining.
−
Clean up the site and revegetate any denuded slopes.
Note: It is good practice to work from the lowest to the highest point. That way if work is interrupted for any reason at least part of the drainage system will function correctly in the event of any rainfall occurring before completion.
C5-5
Subsurface Drain Construction The following sections detail construction methods for the following subsurface drains:
C5-5.1
−
Longitudinal drains
−
Lateral drains
−
Blanket drains
−
Horizontal and vertical drains
−
Pipe drain using unslotted pipes
−
Sump installation
Longitudinal Drain Construction This is the most commonly used form of subsurface drain used for track drainage. The basic construction steps are as follows: −
Survey the site.
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−
Establish the reference points. These may be paint marks on the rails or star pickets. The purpose of these marks is to provide points from which the depth of the trench and pipe invert level may be measured accurately. (See Section 5.1).
−
Excavate to the desired level. The type of equipment used to excavate the trench differs from location to location, depending on such parameters as; access, material, volume to be excavated and clearances for the safe operation of equipment.
−
The depth of the excavation depends on the pipe location, and outlet and inlet requirements. For pipes running parallel to the track, the minimum pipe cover is to be 600mm below the design cess level. Where this is not feasible, the minimum pipe cover is to be 300mm below the design cess level or 1000 mm below the adjacent rail level (whichever produces the lowest invert level). Note: the design track formation profile shall be as set out in TMC 411. The width of trenches should only be as wide as necessary to ensure proper installation and side compaction. The minimum width shall be pipe diameter plus 150mm on each side. For longitudinal drains located either within 2500mm of the track centre line or between tracks where track centres are less than 6000mm, the minimum trench width shall be pipe diameter plus 100mm on each side. 150/100 Pipe dia
150/100
Figure 28 - Trench width Installing drainage system. The method of installing this type of subsoil drain depends on the type of subsoil and other conditions encountered. (a). Impervious soil - aggregate filled excavation (that is, most clays are relatively impervious). Refer also to Figure 15. i.
Lay the geotextile in the bottom of the trench. Where joints need to be made in the geotextile a minimum overlap of 1 metre should be made.
ii.
Place a layer of aggregate in the bottom of the trench approximately 50mm thick. The aggregate used for this should be 20mm nominal diameter aggregate.
iii.
Lay the pipe sections, one section at a time on top of the aggregate.
iv.
Place pits/sumps and remove knockouts
v.
Check and adjust the pipe level and grade if necessary by packing aggregate under the pipe.
vi.
Place aggregate around and over the pipe, tamping the aggregate on the sides of the pipe as the trench is filled. Once the pipe is covered, complete the filling of the trench compacting the aggregate in layers no greater than 150 mm thick, using a vibrating plate compactor or similar.
vii. Fold geotextile over the top of the trench, ensuring that the ends are overlapped a minimum of 300mm. viii. Place a minimum 100mm thick layer of aggregate over the geotextile and grade the surface ix.
Pack knockouts from the inside of the pits using sand/cement mortar (or geotextile if detailed in this manner)
x.
Complete associated works (eg pit lids/pots, ballasting etc).
(b). Pervious soil – aggregate filled excavation (for example sandy soils). Refer also to Figure 16. When laying a drain in pervious soil it is necessary to place an impervious layer in the base of the trench. Typical impervious layers are concrete, cement or lime stabilised fill or clayey fill. © Rail Corporation Issued December 2009
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The impervious layer is to be 100mm thick at the edges of the trench and slope towards the centre of the trench where it is to be 50mm thick. Once an impervious layer is installed, the remaining construction steps are the same as steps "i" to "x" for drains in impervious soils above. (c). Geotextile wrapped pipes Sometimes it is beneficial to wrap the pipe inside a geotextile rather than around the outside of a trench. In this case repeat the procedure of (a) with the exception of: (i) the geotextile is wrapped and lapped a minimum 300mm around the pipe and (vii) is not required. (d). Earth Filled excavations - unslotted pipes i.
Place bedding sand/roadbase in the trench and compact as per the design
ii. Lay the pipe sections, one section at a time on top of the bedding. iii. Check and adjust the pipe level and grade if necessary. Adjust pipes by removal of base material or ramming additional bedding under the pipe. Alternatively, slings may be used around pipe ends. iv. Place pits/sumps and remove knockouts v. Place side zone material and compact to the required relative density as shown on the drawing. vi. Place a 150mm maximum layer of material over the pipe and use a vibrating plate compactor or similar to compact the fill to the required relative density. Repeat backfilling and compaction until fill is at final level vii. Pack knockouts from the inside of the pits using sand/cement mortar (or geotextile if detailed in this manner) viii. Complete associated works (eg pit lids/pots, ballasting etc). (e). Limited length due to outlet restrictions. In some locations a subsoil drain cannot be located deep enough to prevent it being disturbed by track maintenance machines. In this case the pipe may be wrapped in geotextile, then placed in the trench on a bed of aggregate to allow any adjustments to the level and grade of the pipe to be made, the trench may then be filled with a suitable pervious fill and compacted in layers. (f). Ash Pockets Where isolated pockets of ash are encountered, an impervious membrane may be placed in the trench before the fabric is laid. This membrane should cover the ash pocket and extend approximately 2 metres either side of it. The rest of the drain is constructed as set out in (a) above. This method is used only where the soil on either side of the ash pocket is impervious, otherwise the drain is constructed as per (b) above. If an impervious membrane is not available the section of the drain above the ash pocket may be constructed as for a drain in a pervious soil. See Figure 29 for the treatment of ash pockets.
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Geotextile
Impermeable membrane
Soft material (eg ash)
Impermeable membrane Subsoil drain
Ash pocket
2m
2m
Figure 29 - Construction of a drain over an ash pocket.
C5-5.2
Lateral Subsurface Drain Construction This type of drain is commonly used to drain under turnouts and isolated water pockets in embankments. For turnouts the construction of lateral drains is the same as that for longitudinal drains, the main difference is the depth of the pipe below rail level which is a minimum of 1200 mm. For embankment drainage, a lateral trench is excavated to the desired level, using a backhoe or similar. Once the trench is excavated to the desired level, the base is graded to fall away from the embankment centre. The construction methods are the same as for longitudinal drains (point (d) above).
C5-5.3
Blanket Drain Construction This type of drain is most commonly found at the base of embankments. Blanket drains are usually constructed during embankment construction, embankment widening or repairs to a slip. The construction steps are as follows:
C5-5.4
−
Excavate. For embankment widening or slip repair, steps should be cut into the existing embankment (see RailCorp Manual TMC 411)
−
Level and compact the base with a fall away from the embankment centre.
−
Lay out the geotextile. Any joints should have a minimum 1 metre overlap.
−
Place aggregate, usually 20 - 53 mm aggregate up to 300mm thick. (This should be laid and compacted in layers).
−
Fold sides of geotextile up over the top of the aggregate, then cover with a layer of Geofabric over the top of the aggregate.
−
Place riprap (100 - 150 mm stone) over the exposed face of the drainage blanket as protection.
−
Build up the embankment to the desired level and compact in layers.
Other Types Included in this section is the construction of horizontal and vertical drains. These drains are not often used for track drainage and consequently will not be dealt with at this stage, with the exception of the following. The most commonly used vertical drain is used to drain water from behind retaining walls and bridge abutments. This drain consists of a geotextile layer placed at the back of the wall and connected to a pipe at the base of the wall.
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Water reaching the geotextile can flow along the plain of the fabric that is down the back of the wall, and is then removed by the pipe at the base. This may also be combined with horizontal layers of geotextile to collect water seeping through the embankment or backfill behind the wall, which is conducted towards the vertical drain and then to the carrier pipe and removed. This type of drain may be placed during construction and backfilling, or an area behind the wall can be excavated for their installation.
C5-5.5
Construction of an Unslotted Pipe Drain Follow the procedure as per (d) above.
C5-5.6
Sump Installation Sumps shall be spaced at 30 to 50 metre centres, except through platforms where spacing shall be 20 to 30 metre centres. Reduced centres may be applicable in the 6-foot between tracks to account for track curvature. At the location at which a sump is to be placed the trench is widened and deepened to accommodate for the sump. The base of the trench is then levelled and covered with a layer of compacted sand or road base, which is a minimum 150mm deep. This layer may be added to so that the sump is positioned at the correct height. Prior to placing the sump the wafer of concrete covering the inlet and outlet is knocked out to approximately the desired size. Drains using slotted pipes and geotextile are connected to sumps as shown in Figure 30 below. Once the pipe is in place any remaining gaps between the pipe and the sump are grouted. The trench is then filled and compacted. Sump cage Grate Sump
Geotextile Aggregate
Slotted pipe
Fabric is wrapped and twisted to hold back stone
Fiqure 30 - Method of joining longitudinal subsoil drain to sumps.
C5-6
Other Types of Construction Other construction methods that may be used are: −
Pipe jacking
−
Tunnelling
−
Augering
−
Cast in place
These are seldom used for track drainage, and therefore will not be dealt with.
C5-7
Inlets and Outlets Some typical examples of inlet and outlet protection used are:
−
Precast concrete units
−
Grouted sand bags (Figure 21)
−
Concrete (Figure 22)
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−
Reno mattresses and gabions (Figure 23)
−
Revetment mattress (Figure 24)
−
Spalls grouted or hand packed (Figure 25).
Inlet and outlet protection is to be installed as shown on the Drawings and in accordance with manufacturers’ instructions. Typical details for a gabion headwall are: 500 min
100 min 100 min
500 min
500 min
2000
300
Figure 31 – Gabion Headwall – Typical details
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Chapter 6 Maintenance of Track Drainage C6-1
General Good track maintenance and effective track drainage are closely associated. The stability and condition of the track and the formation is intimately related to the effectiveness of the drainage systems. The track’s drainage system must be carefully maintained. The consequences of poor or blocked drains can range from small areas of foul ballast to large washaways or embankment failures. Water must be drained away from the track as quickly as possible, so that it does not affect the track stability. Where sub-drainage work has been carried out; the outlets must be kept clean to allow water to run off. The cesses in cuttings must be kept formed so that the water will run at the toe of the batter. On banks the cesses must be graded away from the track. Where bog holes exist, ample metal ballast should be kept on hand to replace the continued loss of metal through fettling. The attention of the Team Manager must be drawn to this so that he may have sub-drainage work carried out, when practicable. Effective drainage is a major factor in minimising maintenance work necessary on welded track.
C6-1.1
Drainage Principles The basic principles of drainage are that drains will: Allow water to drain away: It is important that water is drained away from the track structure as quickly as possible. Keep water flowing: If there are low spots in the drainage path water will pond and will saturate the sensitive track structure and weaken the material in that area. Control the path of water: Water should not be permitted to flow from the drain into areas that will be damaged by water e.g. flowing into sink holes or from the cess back into the track because of debris in the cess. Control the flow rate of water: Water should not flow too slowly as to cause saturation (ponding) or too rapidly as to cause erosion. Reduce erosion: certain materials are prone to erosion and require additional treatment otherwise drains block rapidly or slopes become undercut and cause instability. Keep water as far away as possible: Where the countryside is very flat and recommended grades cannot be achieved, water should be drained away from areas that can be damaged by saturation e.g. allow water to pond at the railway boundary rather than the toe of the embankment.
C6-1.2
Indications of ineffective drainage The following are indications of ineffective drainage: −
Foul or dirty ballast
−
Pumping sleepers
−
Rotting sleepers
−
Bad top and line
−
Silted drains
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−
Pumping joints and crossings
−
Pools of water
−
Broken or blocked pipes.
If drainage is ineffective,
−
Look for the cause, and
−
Fix the problem.
Pools of stagnant water lying near the track must be drained and the problem that caused them rectified. The proper action is:
C6-1.3
−
Locate the problem
−
Drain the pools
−
Check all drains have proper cross-fall and grading.
Possible causes of ineffective drainage Possible cause of ineffective drainage are:
−
Broken pipes
−
Street gutters
−
Septic Tanks
−
Unlawful diversion of water by Property Owners.
To maintain good drainage the Team Leader must:
know where the drains are
know which way they flow
know where they discharge
clear any blockages immediately
−
repair any weak spots.
If Team Leaders cannot do the necessary work, they should:
−
report it to their Team Manager
−
request extra staff, material, or equipment.
Backhoes , bobcats, small bulldozers and dumpers are some equipment which can be used to clear drains.
C6-2
Surface Drainage
C6-2.1
Maintenance Considerations Maintenance operations carried out on surface drains usually fall into one, or a combination of the
following:
−
Weed control.
−
Removal of debris from other track maintenance activities.
−
Removal of sediment.
−
Regrading.
A build-up of weeds within the surface drain tends to slow the passage of water through the drain,
which, in turn, allows sediment to settle leading to a blockage of the drain. Such a blockage can
render a drain useless and lead to a decline in the effectiveness of other drains in the system. For
example, if a cut-off drain at the top of a cutting becomes blocked water may overflow the drain,
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run down the cutting face increasing erosion of the face and the cess drain will eventually block up due to the additional sediment load. Weeds may be removed using normal weed control practices. Sleepers and rails, for example, left in the cess drains after maintenance work, tend to act as dams allowing water to pond alongside the track and seep into the formation. This will also allow sediment to settle. Thus old sleepers and rails should be removed to a suitable dump at the completion of any track work. When a drain fills with sediment, whether it is due to a blockage or a flat grade, this sediment should be removed and the drain regraded if necessary. The type of equipment used to remove the sediment depends on the extent of the blockage and the accessibility (equipment used may range from a shovel to a gradall). Regrading is sometimes necessary due to scouring or to increase the grade of the drain slightly to reduce the amount of sediment that can settle in the ditch (channel). See Table 8 for a summary of Surface Drain Maintenance. Where cutting faces are exposed, thus undergoing unnecessary cutting face erosion leading to an acceleration of sediment build-up in cesses, these should be protected. Forms of protection commonly used are spray grasses, or seeding, sodding and shotcrete. Type of drain CESS DRAIN
Problems encountered
Possible remedies
Blockages - Weeds
Poison
- Old sleepers and railetc
Should be removed and cess regraded. Old sleepers and rails should be removed when replaced and not left lying in the cess drain, if not removed from site sleepers should be gathered up and disposed of.
- Other discipline infrastructure
Approach other disciplines about equipment relocation.
Spillages and Spent ballast.
Remove and regrade cess.
Blockages may lead to - Silt build up - Water ponding
Clean out cess drain and regrade if necessary.
- Overflow Uneven grades
Regrade cess.
Scour
May be possible to widen cess or regrade cess to decrease water velocity, if not the cess should be regraded and/or lined.
- Due to high water velocities Often found on down stream side of blockages CATCH DRAIN
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As above Animal (rabbit) burrows are also a problem in some areas
Eradicate or remove animals and fill in burrows.
Poorly graded
Regrade the drain.
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Problems encountered Scour - Especially at outlets for catch drains above cuttings, where drains tend to be steep producing high velocities
Possible remedies Use more regular outlets. Therefore, producing less water at lower velocities at each outlet. Or regrade and/or line the drain.
MITRE DRAIN
As above for cess drains. Greatest problem is Scour
Regrade or line the drain. If necessary provide some means of retarding the flow out of these drains
GRADED SHOULDER
Water ponding
Regrade the shoulders so that they fall away from the track.
Table 8 - Summary of maintenance of surface drains.
C6-3
Subsurface Drainage
C6-3.1
Outlets Outlets are the most critical element of a subsurface drainage system because they are susceptible to events that can impede the free flow of water. The main concerns are blockages due to weed growth, siltation of the adjacent ditch or stream, debris from the track or slope and the activities of animals or man. A system of marking outlets of subsurface drains should be implemented to enable easy location of outlets. It is recommended that outlets and outlet markers be inspected and repaired, if necessary, as part of routine maintenance at least once a year. As with the inspection of other drainage system components this should preferably be carried out in the period of least rainfall.
C6-3.2
Pipes and Sumps Pipes and sumps are susceptible to blockages due to ballast and rubbish from the track, tree roots in search of water, siltation and pipe breakages or crushing. Sumps may be cleaned by either digging the sediment, ballast and rubbish out of the silt traps or by using a vacuum device (mainly used for deep sumps). Sumps filled with ballast are most effectively cleaned using post-hole shovels, but these are ineffective for the removal of fine noncohesive silt. Square nose shovels of varying widths are suitable only where sediment fills the silt trap. Where a sump is deeper than two metres it becomes too difficult to clean using shovels. In this case a vacuum device may be used. Once the sumps have been cleaned the adjoining pipes may be cleaned if necessary, by either rodding, hydroblasting or similar. Rodding of the pipes involves the pushing of a circular plug, of slightly less diameter than the inside of the pipe, through the pipe using flexible rods. Rodding is done working from sump to sump starting at the downstream end. Any sediment or other debris pushed out of the pipe is then cleaned out of the sumps. Hydroblasting involves the removal of sediment by using a low pressure, high volume water jet, since high-pressure low volume water jets tend to damage pipes. Hydroblasting is most effectively carried out using experienced Contractors. The process involved is as follows: Sections of the pipe network are cleaned from sump to sump working from the outlet pipe. Various nozzles are used to break up any encrustations and remove debris by either jetting it out into the sump or by relying on the volume of water and the grade of the pipe to create a self cleaning effect and remove any sediment.
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Once this operation is completed the sumps are cleaned either by the methods previously
mentioned or by sludge pumps.
This process is then repeated in the next pair of sumps and so on.
Care must be taken to replace any displaced sump grates or covers removed during the cleaning
and inspection of the drainage system.
See Table 9 for a summary of Subsurface Drainage Maintenance.
Problems Encountered
Type Of Drain Pipe, Aggregate Geotextile Filter and Sump Type Drain (Longitudinal Drains)
Sump Grates and Covers
Blockages:
Possible Remedies Clean out rubbish and ballast.
- Rubbish & Ballast - Silt
Hydroblast or rod pipe. Remove sludge with sludge pump or shovel.
Scour outlet
Provide scour protection and/or decrease water velocity.
Blocked by
Remove cover and or grate, clean sump if necessary. Clean and replace grates and cover. Remove rubbish etc. from site.
Rubbish and Silt
Aggregate & Geotextile Drains e.g. Blankets
Blocked Outlets
Outlets
Scour
Provide scour protection and or decrease water velocity.
Blockages
Clear away vegetation from outlet. Clear any other debris away from outlet e.g. spent ballast etc.
Remove vegetation. Clean outlets ensure no water ponds at outlets.
Table 9 - Summary of Maintenance of Subsurface Drains
C6-4
Typical problems and solutions This section looks at typical drainage problems, suggests possible reasons for their occurrence and practical maintenance solutions which range from simple cleaning to upgrading drainage.
C6-4.1
Cuttings Drainage problems are exhibited by:
−
Water ponding
−
Poor track alignment and level through the cutting
−
Pumping of mud up through the ballast
−
Rock pumping.
The main causes of these problems are:
−
Poorly graded cess drains.
−
Blocked cess drains i.e. drains silted up due to cutting face erosion or debris (e.g. sleepers
and spent ballast etc.).
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Foul ballast i.e. spillages from coal and wheat trains or mud causing the water to be trapped in the ballast. Another possible cause is the damming of water caused by the dumping of spoil by ballast cleaners at the ballast toe.
Another problem associated with cuttings is where cut off drains have been provided but not maintained. Thus water can pond within these drains resulting in the saturation of the cutting face which would lead to slipping, slumping or piping of the cutting face. This may also allow water to overflow the drains and run down the cutting face causing excessive cutting face erosion, which in turn causes the cess drain to silt up quicker. There are a number of solutions to these problems depending on the size of the cutting and the number of tracks. These are:
C6-4.2
Narrow or Steep Cuttings Depending on the severity of the problem it may only be necessary to clean, regrade the cess and ballast clean the problem section. The other alternative is to install subsoil drains. The cess is deepened and a subsoil drain installed, the ballast is then allowed to fall over the drain. Thus if the surface (cess) drain becomes blocked (i.e. silted up) the subsurface water is still being drained away from the formation. This system can also be used on multiple track, provided the formation is in good condition and graded towards the cess drains. Otherwise the formation may need to be reconstructed.
C6-4.3
Wide Cuttings In wider cuttings or if widening of the cutting is possible, the cess drains need only be deepened and widened so that water is drained out of and away from the track and does not prevent water flowing away from the track. This method should be used where easy access is available allowing regular maintenance to be carried out. Note: Cutting faces should be stabilised to reduce erosion and subsequent silting up of cess drains. For example spray grassing.
C6-4.4
Embankments The main drainage problems associated with embankments are; water being trapped in the ballast due to fouling of the ballast (either from spillages or mud) and the build up of spoils from previous ballast cleaning operations. Another problem is that of water ponding at the embankment base, which may lead to slips. This water may cause saturation of the embankment base consequently causing further consolidation and settlement of the embankment. To prevent water being trapped in the ballast, leading to formation failures, the shoulders of the embankment must be kept clean and graded away from the track. Thus windrows of spent ballast must not be allowed to build up on embankment shoulders. Depositing ballast cleaning spoil over the side of the embankment stops water being trapped in the ballast but can cause water to be trapped in the embankment itself. The spent ballast tends to from an impermeable layer over the outside of the embankment. Catch drains must be installed and maintained such that water is prevented from ponding at the embankment base. An alternative to catch drains in flat areas is to grade surrounding ground away from the embankment such that if water does pond in the area, it is away from the embankment base. At areas of heavy seepage through embankments, a transverse subsoil drain should be installed to drain the water from the embankment, thus reducing the possibility of embankment saturation and any resulting problems.
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On multiple tracks where drainage problems have been encountered it may be necessary to install a transverse drain with suitable outlets to effectively drain water from the ballast. Note: Embankment faces should be stabilised to reduce erosion problems (e.g. spray grassing or sodding or geotextile, etc.).
C6-4.5
Soft Spots or Bog Holes Because this condition is often the result of water collecting in depressions in the formation caused by inadequate or poorly maintained drains the first consideration should be to upgrade or clear existing drainage. The provision of suitable drainage to preserve the stability of the formation is of prime importance.
The disposal of the impounded water from these depressions is achieved by excavating to the
lowest level and providing suitable permanent outlet drains.
Before deciding the actual method of treatment, the local conditions must be investigated. The
objective of the investigation is to try and determine the source of the water and to obtain the depth
of the water pocket or depression.
To investigate a soft spot, trial holes are sunk at about 2m intervals. This will determine the depth of ballast and soft formation. This enables selection of the best type of drainage system or solution to the problem. The procedure to follow in the solution the problem is as follows: 1. Determine the position and depth of the outlet drain or 'tap' drain by using trial holes to locate the depth of ballast or the soft area. 2. Excavate and remove the 'soft spot' and foul ballast. The lower level of the trench for any sub drains used must be graded longitidinally at least 1:100 toward the outlet drain. Sub drains should be lined or covered with a geotextile fabric and filled with clean new ballast. 3. Cess drains are also upgraded so that surface water will not penetrate the treated area upon completion of the work. Where possible, they should be widened and graded uniformly to the mouth of the cutting. This will help in allowing the water to run freely away. 4. If the capping layer has been disturbed it is then restored with crossfall angled towards the drains. 5. The track is restored with 'clean' new ballast and resurfaced.
C6-4.6
Scours and Washaways During heavy and prolonged rain, the normal drainage channels provided may not be able to deal with the extra water flowing through them, with the result that flooding occurs. In flat country, embankments may become submerged and saturated. If the water level rises uniformly on both sides of the bank, there will not be a great amount of water flow. As a result, little damage will occur. If, however, the flooding is confined to one side of the line, bridge and culvert openings will be liable to scour. Should the water run over the top of the track, very serious damage can result. The amount of damage will be dependant on the velocity or rate of flow of the water. Any steps taken to reduce the velocity will, therefore, assist in reducing damage. The danger point is reached as water first commences to trickle over the formation. Scouring then starts, first in the ballast and then in the formation. If there is a large difference in the water levels on the two sides of the bank, the velocity will be high and damage extensive.
C6-4.6.1
Temporary Repairs During heavy flooding, washaways may be numerous. They may range from small sections of ballast washed away to deep cuts where the whole embankment has been removed. The method of affecting temporary repairs will depend on the nature and size of the washaway and also the materials and equipment available. If the ballast only is scoured out and it is not possible to get ballast to the site, quick repairs may be made by redistributing the remaining ballast. This will lower the track into a long 'slack' and is only
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a temporary measure to restore traffic. More permanent repairs must be completed as soon as possible. Where shallow scouring of the formation occurs, continuous sleeper pigsties may be used. For deeper scouring, pigsties, trestles and temporary beams will be required. Permanent repairs will then require the closure of the track and reconstruction of the embankment.
C6-4.7
Slips This type of earthwork failure comes within the experience of nearly every person associated with track maintenance. They need not be large to cause serious damage and are very dangerous in that they can occur suddenly and without warning. It is desirable, in the initial construction of the track, to avoid unsuitable soils. However, track staff are generally involved with tracks constructed for many years. As such, conditions must be dealt with as they are found. Terracing and flattening of slopes will assist in bringing about stable conditions. Cuttings, in soft material or in slopes liable to fail, may be widened to provide space for falling debris clear of the track. Material removed from cuttings should not be placed on or pushed over embankment sides without prior investigation of the embankment stability. Embankments can only be widened using the correct procedures. Advice on the appropriate batter slope, terraces and procedures for the widening of embankments should be sought from the Geotechnical Services Section. Small slips may be foreseen and prevented by the removal of loose material or the building of some form of protective structure. The removal of only the 'toe' of a slip will lead to increased sliding. When it is necessary to clear the toe, only the minimum quantity to permit the passage of trains should be removed. Mud flows, which result mainly from heavy rainfall, cannot always be foreseen and prevented but continual maintenance of top drains will assist in reducing their incidence. Slips may be of several types or include features of each type.
C6-4.7.1
Flow Movements The soil material of a hillside or side slope may become so saturated with water that it moves downward in the form of a mud flow. The rate of flow may be slow or rapid depending on the degree of saturation and type of material. The slopes from which the flow starts need not be steep if excess water is present. The potential effect of this type of slip is to cover the track, push it out of line or destroy any form of support or retaining wall.
C6-4.7.2
Shear Failure Sometimes an embankment or hillside is composed of soil without any great strength or cohesion between its particles. It may be standing too steeply and cracks may develop which will permit the entrance of water. Movement or a large part of the slope takes place slowly at first but can become very rapid as complete failure takes place. This type of slip may occur at any time, even many years after the railway is constructed. The effect on the track is seen as a depression if the movement is minor or a total loss of support if major movement occurs.
C6-4.7.3
Slope Adjustment This is a natural occurrence due to erosion. Quantities of spoil or rock fall away from the sides of cuttings and fall onto the track. They may be composed of fine material or rocks that are large enough to derail trains.
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Protection against the damage can be afforded by periodically removing any loose stones and by the provision of a wide bench at the toe of the cutting in which debris may collect clear of the track.
C6-4.8
Platforms The main problem associated with platforms is the ponding of water that consequently causes formation failures, exhibited as poor track alignment, pumping sleepers and bog holes. The solutions available depend upon the severity of the problem. These are: −
Clean all sumps and pipes
−
Install a suitable drainage system in the six foot
−
Recondition track and install subsurface drainage system
−
Completely excavate problem area and replace with densely compacted fill up to the next formation level, then provide a 150mm compacted granular capping layer and 300 mm of ballast cover. During reconstruction install a subsurface drainage system.
Also at stations with island platforms there is often a problem with water ponding at the ends of the platform. This can be remedied by placing a sump in the six-foot connected to an existing drainage system or suitable outlet. Note: Runoff from station buildings and platforms may be piped into sumps. This provides relatively clean water which can be used to help flush drainage systems.
C6-4.9
Turnouts With the increased axle loads and cyclic forces exerted on turnouts it takes very little water for them to start pumping mud up through the ballast, consequently fouling the ballast and compounding the problem. Some solutions to this problem are as follows: −
Deepen and widen the cess drains on each side to drain water from the ballast and keep it clear of the formation
−
Install subsurface drains under problem areas during turnout reconditioning or renewal. Major problem areas are under heel blocks and crossings. These are points where the most pounding (greatest impact load) tends to occur.
In come cases during turnout and crossing renewals asphaltic concrete has been used as a capping layer to help increase the impermeability of the formation thus giving it a longer life.
C6-4.10
Yard Drainage The problems associated with yard drainage are similar to those of any other track work except on a larger scale. Where on most lines the drainage must cater for between one and four tracks in yards there are usually many more. Also yards tend to be constructed on very flat areas, thus there is very little fall available for surface and subsurface drainage systems. The simplest solution for any drainage problems in yards is to clean and regrade cesses and provide regular outlets in the form of sumps such that the best possible grades can be applied to the surface drains. The most effective method is to have the formation graded as shown in Figure 31 below.
Figure 32 - Typical "saw tooth" formation used in yards Subsurface drains are located at the low points. If large flows are expected it may be necessary to install carrier pipes. Carrier pipes may be placed at a deeper level thus allowing the grades of subsoil drains to be increased between sumps.
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Subsurface drains
Carrier pipe
Figure 33 - Carrier Pipe Arrangement
C6-4.11
Bridge abutments and retaining walls Unless adequate weep holes are installed during construction and kept clear by routine maintenance, weep holes tend to block, trapping water behind the abutment or retaining wall. This causes saturation of the earth (fill) behind the walls, which can lead to further consolidation and settlement of the fill. Weep holes are required at and above the capping layer level as well as at the base of a wall. Weep holes should also be located at regular intervals down the wall, thus if the bottom holes become blocked the upper ones can still allow some water to escape. Existing weep holes should be cleared during routine bridge maintenance. New holes should be bored through the wall if no holes exist or the existing holes are inadequate, especially if there are no weep holes present above the capping layer level.
C6-5
Preparation for Flooding
C6-5.1
General Each Region is to have an emergency plan for dealing with major flooding that would effect train operations. Major flooding can occur with little warning and quick action may be necessary without time to prepare. The "Flood Plan" is to be documented and regularly updated. Copies are to be issued to each Team Manager and other senior staff. In particular, a copy is to be part of the "Handover Notes" for relief officers. The Regional staff should be the railway source for forecasting the effect of a flood on railway facilities and be the adviser to Network Control. The Civil Maintenance Engineer is to arrange this service when a flood is forecast.
C6-5.2
Historical information The collection of data during flooding is most valuable in planning measures which will reduce or avoid damage by future floods. The heights of water levels at bridges, culverts and on railway embankments should be marked so that flood levels may be recorded. At large bridges, the water level may be different at each end or on up and down stream sides. Levels at all of these points should be recorded. Any appreciable difference in the up and down stream flood levels at a bridge may indicate an inadequate waterway. The records of previous floods in each river in the Region are to be kept up to date. Frequency and severity of flooding are usually available on Working Plans and office files. Other instructions require all flood heights to be recorded. Local Councils and other local bodies can provide a wealth of information on flood heights that will allow up river peak height information to be related to timing and severity of railway bridge flooding levels.
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Local papers and local residents can also advise on the time the river takes to rise, water movements and other essential local knowledge. Bureau of Meteorology Rainfall patterns assist in assessing runoff rates, saturation figures as well as river peaks and times. From all available information a river flow chart should be prepared that will provide an accurate forecast of the effect of future floods in the river systems on railway facilities once upriver reports are received.
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Chapter 7 Documentation Requirements C7-1
Introduction The aim of this section is to provide a guide for external consultants in the preparation of design drawings and hydrology reports for minor track drainage projects within the rail corridor. It also covers external party development works discharging onto or through the rail corridor. The requirements are also applicable to RailCorp field staff doing track drainage design. This guide is provided to achieve standardisation of documentation associated with track drainage design and external works discharging onto the rail corridor. All documentation is to be retained on the project design file. Minor drainage works within the railway corridor include open cess, pipes, pits, covers such as lobster cage, and minor under track drainage openings.
C7-2
Review Process When the drainage design/hydrology report is at minimum 90% completion, drawings/reports are to be submitted to RailCorp’s Design Delivery Manager (DDM), who will forward them to the Bridges and Structures Design Section for review. The review will be conducted in two parts: 1.
Drawing review
2.
H ydrology/hydraulic review.
The following documentation is required for this process: Drawing review: −
1 hardcopy set of prints - A3 size (or softcopy pdf files).
Hydrology/hydraulic review: −
2 hardcopies of a Hydraulic/Hydrology report (or softcopy pdf files). Where the nominated Civil reviewer determines that a full hydrology report is not required, then a summary document shall be prepared as a minimum – refer to section C7.4.
−
A softcopy of the hydrology/hydraulic computer design file (eg ‘Drains’ drn file) or hand calculations shall be provided.
The time for Railcorp to undertake the review is highly dependent on the availability of RailCorp staff and their existing work commitments. Typically this may be 2-3 weeks but may extend up to 6 weeks in some instances. It may be a requirement for the Reviewer to undertake a site inspection, in which case, it may be necessary for the consultant to attend an on site meeting. The Reviewer will look at the information provided and highlight any changes/additions/comments that may be needed to meet RailCorp requirements. Once acceptance has been given (and all modifications incorporated), then the consultant/designer must provide final acceptance documentation. For acceptance and final sign-off, the following documentation will be required: −
1 signed set of drawings (A1) size with all necessary signatures.
−
CAD drawing files in MicroStation Version 8 format and on labelled CD.
−
2 signed copies of the final hydrology report.
−
A softcopy of the final hydrology/hydraulic computer design file.
A senior member of the Bridges and Structures Design Section will sign the documentation as ‘accepted’ for use by RailCorp. The drawings will then be registered in the Plan room. The DDM
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can then arrange copies of the approved drawing for distribution to the Consultant and appropriate RailCorp field staff. RailCorp acceptance signatures on drawings prepared by Consultants designate only that the drawings appear to be consistent with the requirements of the design brief and that the presentation is satisfactory. No dimensional, drafting or design check will be undertaken by RailCorp. The responsibility of the structural adequacy, safety, compliance with codes & legislative requirements and dimensional accuracy remains with the consultant. Note: Any costs associated with undertaking changes requested in the review process will be borne by the Consultant.
C7-3
Drawing requirements All drawings are to comply with the relevant sections of the RailCorp CAD and Drafting Manual – ED 0022P, ED 0026P and ED 0027P. Typically, most rail drainage projects are site specific in that they have different site constraints, varying terrain and unique rainfall catchments. For this reason, RailCorp has not developed standard drawings. However, it is fair to say that many details of track drainage remain generic. The following aspects are considered the minimum requirements that should be detailed on track drainage drawings. General −
All drawings are to be completed using CAD (Microstation or AutoCAD). There is to be only one drawing sheet per CAD file.
−
Drawings are to be detailed using standard RailCorp drawing sheets (A1 size). Electronic file of the standard RailCorp drawing sheets in dwg format will be provided to the Consultant
−
Each drawing is to have a unique RailCorp drawing number (CV No’s). These numbers will be supplied on request. Note: if more drawings are required than originally requested, then additional numbers must be requested. These numbers probably will not be a continuation of numbers previously given.
−
The RailCorp drawing numbers shall be used for cross references and not drawing sheet number or consultant internal filling numbers.
−
Title blocks are to be filled out to RailCorp Standard as detailed in the CAD Manual.
Plan −
Drainage layout drawn at a minimum scale of 1:200 with Sydney shown on the left.
−
The layout shall include identification or marking of drainage pits/sumps eg pit P1, P2 etc.
−
All railway tracks (including turnouts, crossovers and sidings) to be shown and labelled eg Main West - Down
−
Kilometrage marks to be shown along the track – say at 20m centres. Text labelling at even 100m centres (20.100km). Note: OHWS structure numbers may not coincide with track km.
−
Show the North point.
−
Indicate and label railway boundary line.
−
Show the top and bottom of cuttings, embankments, drainage channels, depressions etc.
−
Show and label trackside furniture - if applicable (eg signal footings, signal troughing, air lines, train stops, services, face of platforms, retaining walls, bridge abutments & piers etc).
−
Show and label any applicable surveyed items (eg trees, power poles, nearby buildings, edge of roads or access roads etc).
−
Show locations of any external services (as determined from a dial before you dig requestsubmitted by the consultant).
−
Existing drainage to be indicated and labelled (dotted if they are to be removed).
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−
Proposed drainage with dimensions of extent, pipe size/type/class. Arrows indicating flow direction. Each pit to be labelled (e.g. P1).
−
Extent of scour protection (dimensioned and labelled fully).
−
Pipe Jacking - temporary excavation lines shown and pipe jacking direction indicated.
−
OHWS shown with footing outline and structure number indicated. Note: OHWS comprise of a pedestal and either piled or spread footing base. Normally only the pedestal is visible. RailCorp Bridges and Structures Design Section personnel may be able to help determine the footing size/type if a structure number is known.
The plan shall be drawn from and based on a detail survey. However, at the discretion of RailCorp (due to time or budgetary restraints), a schematic layout such as a “track diagram” may be inserted into the drawing. If a “track diagram” is used, then the following note is to be included alongside (in a highlighting box): 1. This plan has been taken from track books and is not to scale. 2. The effects of track curvature and clashes with existing OHWS footings or trackside furniture is to be confirmed on site prior to ordering materials and/or construction. 3. The possible effects of undermining of existing structures have been investigated and are covered in the design.
Locality Map −
Such as a street directory format showing the general area is to be included.
−
Label “From Sydney” & “To Country” at the edge of the map.
−
Show North point.
−
Circle and identify “Site of Works”
Typical Sections −
Are to be drawn at a suitable and legible scale (usually 1:20 is adequate)
−
Show the track, ballast and cross fall of the track formation
−
Show nearest track and dimension the offset to the centreline of the drainage system.
−
Dimension the depth below rail of the pipe system and the pipe cover to ground surface.
−
Indicate width of trench, pipe type/size, geofabric type and fill and bedding material.
Dimension and label compaction layers.
−
If an open channel is adopted, fully dimension the channel and label any scour protection. A table can be incorporated if the channel size varies along the length.
−
If different methods of pipe installation are covered, then a typical section is required for each method (eg cess pipe installation different from undertrack pipe installation)
Longitudinal Sections (for pit/pipe & open channel)
−
A separate longitudinal section is required along all pipe/drainage lines.
−
Draw at a suitable scale (vertical exaggeration can be used to highlight grades)
−
Table along the bottom of the longitudinal section with headings indicating ‘Track km’, ‘design
rail level (low rail)’, ‘cess level’ and ‘pipe invert level’.
−
Indicate track km, rail levels and cess levels at a minimum of 20m centres and at pit locations.
−
Indicate pipe invert level at all pit locations.
−
Indicate grade and extent of pipe runs/open channel.
−
All levels nominated shall be to AHD. Where assumed level is adopted the assumed benchmark must be clearly identified.
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Additional Details Include any additional details that are essential for the construction of the project. These may be
individual details or separate drawings and may include items such as (but not limited to):
−
How new pipes are to be joined in with existing drainage.
−
Energy dissipating device details.
−
Scour protection details.
−
Pipe jacking collaring.
−
Detention basin details.
−
Lobster pot details.
−
Temporary support of existing structures.
Pit Table A pit table is to be included and shall be set up in the following format Pit No
Pit type
Riser
Top
P1
# 1/ 600 sq. x 1200 deep (internal)
# 1/ 300 high riser
1/ 150 high LID.
# 1/ 150 high riser
1/ HD galv. cast iron grate. 1/ Ballast Cage
# - designates step irons required in pit Notes −
Design Criteria (e.g. Design: Average Recurrence Interval (ARI) of 50years, Loading: pipes designed for 300LA + DLA train live load etc.)
−
Pipe/pit notes.
−
Any other notes particular to the project (eg shotcreting)
References (Drawings) −
The first drawing in the set is to reference all other drawings. The remaining drawings need to refer to the first drawing and any other drawing that is referred to in the details on that sheet.
Typical Example Drawings Examples of typical drainage design drawings are in Appendix 5.
C7-4
Hydrology/Hydraulic Report requirements Where a hydrology report is required, the following format is recommended and the items listed are considered the minimum requirements to be incorporated. −
Document Control Table – To incorporate the revision number, revision date, revision details/change and the relevant QA signatures.
−
Table of Contents.
−
Executive Summary (for large reports only).
−
Site description & background.
−
Catchment Details – provide a description of how the catchment has been divided up. For large projects where multiple systems operate and/or catchment break-up is hard to define, then an Illustration/map will be required.
−
Design Methodology – Describe the concept of the design, the software program utilised and a description of the other options considered.
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Hydrology – Describe any relevant hydrology issues and include a table of the hydrologic parameters adopted for the analysis. Example Hydrologic Parameter
Value
Design ARI 1 in 50 years Typical hydrology parameters as adopted in the ‘Drains’ software are: paved (impervious) area depression storage, grassed (pervious) area depression storage, soil type, Antecedent moisture content (1-4), Annual Recurrence Interval ARI, Storm duration range considered, soil permeability %. −
Hydraulics – Describe any relevant hydraulic issues and include a table of the hydraulic Parameters adopted for the analysis. Example Hydraulic Parameter
Value
eg RC pipe Manning’s No 0.002 Typical hydraulic parameters as adopted in ‘the ‘Drains’ software are: minimum pipe slope, minimum pit freeboard, minimum fall across pits, minimum pipe diameter, pit blocking factor, minimum pipe cover, pressure loss coefficients, maximum ponding depth, maximum ponding volume, pipe Manning’s No). −
Analysis Results – Describe the results of the analysis and include a results summary table. In some cases (such as external developments), it may be a requirement to compare various Options or compare between the pre-development and post development scenarios. Example Drainage line
Total Catchment area
Peak Discharge at outlet
Max velocity
Storm event
Pipe 5
1500 m2
40l/s
1.2m/s
ARI 50, 45min storm
(critical case) The table heading and values should be modified to incorporate the type of system being modelled and the critical output relevant to the project. −
Conclusions.
−
Appendix A – Output from computer modelling (from ‘Drains’ this would both ‘input data’ and ‘Results’)
−
Appendix B – Photographs of the site.
For the majority of hydrology reports the above details will be satisfactory. For more complex hydrology scenarios, it may be required to incorporate additional information. Typical examples of this may be when dealing with detention basins, considering backwater effects or examining complex flooding interactions. At the discretion of RailCorp (due to RailCorp time or budgetary restraints), a summary document (report, letter or e-mail) incorporating major aspects of the items above, may be submitted in preference to a report. This will be determined by the Design Delivery Manager (DDM) at the commencement of the project.
C7-5
External party development discharging onto or through the rail corridor The Developer shall provide the minimum supporting documentation as detailed below:
C7-5.1
Hydrology/Hydraulics report A hydrology/hydraulics investigation report shall be prepared by a professional services organisation with the appropriate expertise. The investigation and analysis shall include any
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possible impacts of any additional discharge downstream or backwater effect upstream. This is to include discharge into Council stormwater systems. The report shall be set out as per C7-4, and shall be structured to compare between predevelopment and post-development scenarios. The report shall look at an Average Recurrence Period (ARI) of 50 years and should investigate a range of storms from 5 minutes to 24-hour duration. Note: RailCorp will accept reports done for ARI 100 years (as stipulated by some council’s) as long as the results satisfy RailCorp requirements. It is RailCorp’s policy to reject any submission where the development will adversely affect discharge rates onto or through the rail corridor. To control this, the developer may be required to incorporate a retention/detention system within the developer’s property. Such a system must be covered in the hydrology/hydraulics report. It will also be the consultant’s responsibility to submit a ‘Long-term Maintenance Management Plan’. It is RailCorp’s policy to reject any submission where the development will increase scouring potential within the railway boundary. A drainage solution particular to the site may be required to effectively disperse flow. Alternatively, provision of scour protection may be required. Where the existing track drainage is found to be inadequate to accommodate the site discharge, the developer shall document the upgrade of the track drainage required at their costs. The costs (to be borne by the developer) shall include of upgrading of the RailCorp drainage system.
C7-5.2
Drawings Where upgrading of the RailCorp track drainage system is required, or additional drainage works are required within the railway boundary, the documentation shall be prepared in accordance with the requirements specified in C7-3. Where the developer confines all drainage works to within their property, then a layout plan shall be supplied that conveys the overall stormwater drainage system. This shall include any pipes/pits/basins/channels/downpipes and is to include the outline of the proposed dwelling and ground contour lines (including any ground level survey points taken). Any labelling of pipes and/or pits shall conform to the labelling conducted in the hydraulics/hydrology report. All pipe inverts shall be clearly identified in plan or on cross sections. Any non-related information shall be filtered out. For construction works carried out within the railway boundary, work-as-executed drawings are to be submitted once works have been completed.
C7-5.3
Long Term Maintenance Management Plan Where a developer incorporates a detention/retention system to control discharge, then a ‘Longterm Maintenance Management Plan’ will be required. This shall detail the actions and frequency of inspection and maintenance tasks to effectively maintain the system over its design life. Responsibility shall be clearly defined in the Maintenance Plan eg who is responsible for the nominated inspection and who is responsible for carrying out the maintenance tasks. Any costs incurred by RailCorp as a direct consequence of failure of the stormwater system will be passed onto the developer/owner.
C7-5.4
Other considerations The Developer shall seek the appropriate approval from the affected Council or other relevant Authorities & parties. The cost of design, documentation and construction for any works within the railway boundary shall be born by the developer. The developer must ensure that works are carried out in accordance with railway safety requirements with appropriate RailCorp safety accreditation for all workers.
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Flow Charts Flow Chart 1 – Overall Design Process
1. 2. 3. 4. 5.
Design Investigation. Objective Information required Collection & study of existing information Site investigation Catchment estimation
Drainage System capacity 1. Recurrence interval 2. Design system
Rational method Section C4-4.3
Peak surface runoff flow
Is the drainage system required a surface or subsurface system? Surface
Subsurface
Flow chart 2
Flow chart 3
Produce any drawings and tables necessary for system installation
Design stage complete proceed to construction phase
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Flow Chart 2 – Surface Drainage Design From C3.6 Calculate the peak flow rate QPF
Determine the local soil type such that the maximum permissible velocity and roughness (Table 3) can be established.
Determine the slope from the preliminary investigation survey (Standard is 1 in 100).
Select trial channel size from Table 4.
Calculate the maximum flow rate for the selected trial channel size (Q1)
yes
Is Q1 ≈ QPF?
no
Check the water velocity (V1)
Is the velocity less than the maximum permissible velocity? Table 5
no
Provide either a larger channel or line the drain
yes The channel size & water velocities are satisfactory
If new lining was chosen, then the cost of the lining versus a larger unlined channel should be compared.
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Flow Chart 3 – Subsurface Drainage Design From C4-6.1 Calculate the peak surface runoff (QR)
Is QS =0?
no
Carry out a hydrological study to establish Qs or estimate a value for QS
no
Estimate the value of QC from the size of the upper drain & approximately how full it flows
yes
Is QC =0? yes
QPF = QS + QC + QR (equation 1)
pipe
Is the subsurface drain a pipe or aggregate drain?
Determine the slope of the drain
Determine the slope of the drain (Standard is 1 in 100)
Size pipe for all pipe materials (min dia 225mm) Select pipes from Table 6 such that max flow > QPF determined from eqn 1
Select the size of the aggregate
no
Is the
flow rate in the
pipe acceptable?
yes
aggregate
Choose a value for K from Table 7
Once the required flow is known, the drain area required can be calculated using equation 8
Calculate the strength of pipe required (C4-6.1) Select other drainage components eg. fabric etc (C4-2.3) Compare the cost and availability of each type of pipe
Select a pipe
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Drainage Design Checklist The following checklist is used by RailCorp’s Bridges and Structures Design Section when undertaking track drainage design. It provides a useful guide for consultants and RailCorp field staff.
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Checklist D06
Drainage Design & Investigation Checklist Project Identification Location
Line
Details
Project Number or Identification
File
Design Delivery Manager
Delivery Plan prepared
YES
Target Dates
Documentation
In House
Deliverable requirements
Hydrology/Hydraulics Report Detailed Design Technical specification Review of External design/report
NO External
Investigation Report Scope of Works
Prepared by: Scope of Work/Project Brief − − −
What type of drainage is it? (i) Track (ii) Bridge – UB/Culvert (iii) External Party Development Has a scope of works been provided for Civil Works? Has a project brief been provided? − Have the key design parameters been defined in the scope/brief? − Are Mandatory Legislative or Regulatory requirements defined in the scope /brief? − Have any validation methods been established in the scope/brief? − Is a Technical Maintenance Plan (TMP) required? − Has functional and performance requirements been identified by the client? − Have Interface requirements been scoped (see below)? Are there any future proposals that has been identified (eg– access road, embankment widening, quadruplication, turnbacks, upgrades, track lifts etc).
(i)
(ii)
(iii)
YES YES YES YES
NO NO NO NO
YES YES YES YES YES
NO NO NO NO NO
Do installation or maintenance manuals need to be developed or changed?
YES
NO
Do you know what the operating conditions are? − Class of line − Speed − Maximum Axle load − Operation (inspection/maintenance regime etc) − Usage factors such as numbers of trains − Will the configuration change affect the conditions of operation?
YES YES YES YES YES YES
NO NO NO NO NO NO
Is training required prior to the installation of the design? Have all the stakeholders (both internal & external) been identified.
YES YES
NO NO
−
N/A N/A N/A N/A
N/A N/A N/A N/A N/A
Discipline Interface Track − −
Impact on track vertical & horizontal alignment (eg Is there a need to lift or move the tracks)? Are design track levels (low rail) known?
YES
NO
YES
NO
YES YES
NO NO
Geotechnical − −
Are founding parameters required for drainage design? Is there any possible stability concerns with adjacent structures or embankments?
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Survey − − − −
Is a detailed survey scope required? Is additional survey required to define the catchment area (eg cross sections, additional points) Do existing drainage systems and services need to be identified? Items required survey (cross out/add as appropriate) – exist drainage, pipe sizes, locations of pits, invert levels, inlet/outlet , cess levels, rail levels, existing OHWS+footings, visible services, banks, ballast edge, road edge, site markers, survey pegs, fenceline, trees, surface levels, define wingwalls, water level, local depressions, sketches
Electrical − Are there any Electrical requirements such as electrolysis, transmission lines & other services? Services − Has RailCorp internal services searches been conducted? − Has ‘Dial Before you dig’ external services searches been carried out? − Does it look possible that conflict will exist with structure footings External Bodies? − Has external hydrology reports been carried out in the area (eg local Council/previous reports)? − Are external bodies required to be involved? If Yes, then circle or itemise:
Local Council development Consultant
RTA
………………
EPA
Water Authorities
………………
………………
NO NO
YES YES
NO NO
YES
NO
YES YES YES
NO NO NO
YES
NO
YES
NO
YES YES
NO NO
Land Owner External ………………
Will any proposed configuration changes − Impact on RailCorp’s accreditation with Minister of Transport?
−
YES YES
Require approval from external bodies (EPA, RTA, Water Authorities, Local Councils etc)?
Site Data Site − − − − − − −
Is the proposed works located in an (i) embankment, (ii) cutting or (iii) open track Project type: (i)Renewal / (ii)Refurbishment (UB & Culvert) or (iii) Upgrading for Track Drainage Is there possible impact with existing structures – OHWS, Signal Gantry, Bridges, footings (eg alignment conflicts, undermining of footings, embankment stability concerns)? Site access – is there an existing access road? Is there surrounding drainage systems? – Local Council, RTA, private parties Is there possible scouring concerns or evidence of site scouring? Are details (drawings) of existing drainage available?
(i) (i)
(ii) (ii)
YES
NO
YES YES YES YES
NO NO NO NO
YES YES YES YES YES YES
NO NO NO NO NO NO
(iii) (iii)
What are the Physical Interfaces with Other Property Owners/Stakeholders − − − − − −
Road crossings (including private crossings) Interface between earthworks and other properties Drainage flow to other properties Installations such as pipelines laid within the corridor Private sidings and bridges Other statutory authority requirements eg environment?
Hazard & Risk Identification and Analysis Hazard sources from −
Normal operation
YES
NO
−
Environment
YES
NO
−
Equipment failure
YES
NO
−
Improper use or maintenance
YES
NO
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Risks to − Maintenance or Construction staff
YES
NO
−
Public
YES
NO
−
Operators
YES
NO
−
Other equipment
YES
NO
−
Environment
YES
NO
Has the Design/Analysis considered the effect of potential hazards and risks during −
Construction, including any temporary works required as part of the project
YES
NO
N/A
−
Maintenance
YES
NO
N/A
−
Operation
YES
NO
N/A
−
De-commissioning and disposal
YES
NO
N/A
YES
NO
N/A
Has a proper hydrology & hydraulics calculations been carried out by staff with the proper Engineering Authority (including correct design parameters)?
YES
NO
N/A
For complex hydrology studies – has an external service provider been nominated?
YES
NO
N/A
Have possible mitigation measures been identified and documented?
Design and Documentation Checklist Hydrology & Hydraulics
Hydrology report / Investigations Has the following information been documented −
Document Control Table (revision no, date, details, signatures)
YES
NO
N/A
−
Site Description & Background
YES
NO
N/A
−
Options for refurbishment or renewal
YES
NO
N/A
−
Catchment Details
YES
NO
N/A
−
Design methodology
YES
NO
N/A
−
Hydrology Parameters adopted
YES
NO
N/A
−
Hydraulic Parameters adopted
YES
NO
N/A
−
Other design input (eg survey, recorded flooding, measured values, consultation with councils or authorities)
YES
NO
N/A
−
Analysis Results
YES
NO
N/A
−
Conclusions & Recommendations
YES
NO
N/A
−
Recommendation and concurrence by stakeholders
YES
NO
N/A
Comments:
Detailed Design drawings Has the following information been documented −
Location & description and extent of the drainage works
YES
NO
N/A
−
Drawing sheets and title block to RailCorp current standards
YES
NO
N/A
−
Plan view (Sydney on the left, layout of drainage, existing drainage, banks/depressions, all tracks labelled, nth point, boundary line, OHWS, services, scour protection, flow direction, survey items etc)
YES
NO
N/A
−
Locality Map
YES
NO
N/A
−
Typical sections(offsets to rail, depth to rail, cover to pipe, trench details, compaction layers, geofabric, scour protection, pipe labelled,)
YES
NO
N/A
−
Longitudinal Section along each pipe run (includes, track km, design low RL, cess level, pipe invert levels, grades)
YES
NO
N/A
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−
Relevant notes – design criteria, reference to appropriate Standards and manufacturers.
YES
NO
N/A
−
Drawing References
YES
NO
N/A
−
Additional details (join with existing, energy dissipators, scour protection, pipe jacking, detention basin, lobster pots, temporary support etc)
YES
NO
N/A
−
Specific maintenance requirements eg retention basin – responsibilities and frequency of silt removal
YES
NO
N/A
Does the design document and the information it contains complies with the standards?
YES
NO
N/A
Does the design reflect sound engineering practice?
YES
NO
N/A
Have all known relevant project constraints have been considered?
YES
NO
N/A
Is this document fit for purpose?
YES
NO
N/A
Is it suitable for construction use?
YES
NO
N/A
Is it Suitable for record (plan room) purposes?
YES
NO
N/A
YES
NO
N/A
Are dimensions correct?
YES
NO
Is the drawing to scale?
YES
NO
Is the designer's intention clear?
YES
NO
Is sufficient information given?
YES
NO
Practicality
Can the work be constructed as efficiently as possible?
YES
NO
Consistency
Is the drawing consistent with existing drawings of the same type?
YES
NO
Does the design generally comply with the RailCorp track drainage guide? Drawing Check (Reference – Part 4.8 & 4.9 EM0323) Accuracy
Clarity
If not, can the change be justified?
YES
NO
Standards
Have relevant drafting standards and practices been adhered to?
YES
NO
Is the drawing presentation consistent with RailCorp drafting standards
YES
NO
References
Are all the necessary cross-references included?
YES
NO
Status
Has the drawing status been updated? Eg from tendering & construction
YES
NO
Title
Is the drawing titled according to RailCorp practice?
YES
NO
Corrections
If corrections have already been marked on a previous check print held by the checker, are they included in the current print?
YES
Distribution
Have the drawings been distributed to the relevant stakeholders by the DDM?
YES
NO
YES
NO
NO
N/A
N/A
Verification and Approval The drawing has been signed by the drafter, drawing checker and designer Drafting Checker
Signature
Printed Name
Date
I certify that I have completed the drafting check The drawings reflect the design intent, details and completeness. Designer
Signature
YES Printed Name
NO
Date
I certify that I have completed all required actions.
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Have independent actions have been taken to verify the design as detailed on the drawings Independent Verifier
Signature
Printed Name
YES
NO
N/A
Date
I certify that I have completed an independent design check The design, drafting and checking functions have been carried out by people with appropriate Engineering Authority
YES
NO
The design and drawing reflect sound engineering practice
YES
NO
Reviews at progressive stages have been carried out with the client, to ensure that the design takes into account the client’s needs, the functional requirements and constraints of all relevant codes, standards, regulations, practices and statutory requirements.
YES
NO
N/A
Comments:
The drawing is satisfactory for construction purposes
YES
NO
The design phase for the discipline is complete
YES
NO
YES
NO
Has the relevant information been entered in Bridge Management System (DAD)? RailCorp Engineering Division objectives and standards have been applied Approver
Signature
Printed Name
Date
Signature
Printed Name
Date
I certify that I have reviewed the design and have approved its issue Accepted I have accepted the design for use by RailCorp
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Design Investigation Form Date:___/___/____
Form 1 - Design Investigation. Site Investigation Form. (To be filled out during site investigation). 1
Location. (ie Track Region and kilometrage). ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________
2
Track structure to be drained. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________
3
Condition of existing drainage system (if any). ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________
4
Length of drainage system. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________
5
Restraints? – Inlet/outlet, existing adjacent structures, track curvature etc ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________
6
Estimate catchment area. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________
7
Site access. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________
8
Any specific site safety requirements. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________
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Conduct Services Search. Any visible services noted: ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________
10
Other comments. ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________
11 12
Photographs: to be attached Site Sketch
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RailCorp Engineering Manual — Geotechnical Track Drainage
Appendix 4
TMC 421
Calculation of Capacity Required Form
Form 2 - Calculation of Capacity Required.
a).
Location
_______________________________________________________________ _______________________________________________________________ _______________________________________________________________ _____________________ (b)
Average Recurrence Interval (ARI)
(c)
Size of Catchment Area acting at section under investigation
(d)
ARI
= 50 (All RailCorp)
years
A
=
m2
Convert to km2 x10-6
=
km2
Critical Rainfall duration (tc) Method 1: the normal procedure is to calculate the equal area stream slope by graphing the catchment elevation, drawing a line between the start and finish of the catchment dividing equally the area above and below the line. For ease of calculations below it is assumed this is equivalent to the catchment slope. Mainstream Length (L).
L
=
km
change in height from start of catchment to point under consideration (h).
h
=
m
S =h/L
=
m/km
tc
=
mins
convert to hrs (/60)
=
hrs
tc
=
hrs
convert to mins (x60)
=
mins
Catchment Slope (S) tc = 58 L / (A 0.1 S 0.2) from AR&R (2001) book4 eq’n 1.3
Method 2: using the basic formulae (for Eastern New South Wales). tc = 0.76 A 0.38 (where A=km2) from AR&R (2001) book 4 eq’n 1.4
e).
Hydrology constants. These are looked up on contour style maps from AR&R Volume 2. 2
MAP 1.7 Æ 1hr duration, 2 year ARI
i 1hr
=
mm/hr
MAP 2.7 Æ 12hr duration, 2 year ARI
2
i 12hr
=
mm/hr
MAP 3.7 Æ 72hr duration, 2 year ARI
2
i 72hr
=
mm/hr
MAP 4.7 Æ 1hr duration, 50 year ARI
50
i 1hr
=
mm/hr
MAP 5.7 Æ 12hr duration, 50 year ARI
50
i 12hr
=
mm/hr
MAP 6.7 Æ 72hr duration, 50 year ARI
50
i 72hr
=
mm/hr
G
=
MAP 8 Æ Geographical factor F2
F2
=
MAP 9 Æ Geographical factor F50
F50
=
Figure 5.1 Æ Runoff coefficient for a 10 year ARI
C10
=
i 6min
=
MAP 7c Æ skewness factor G
Calculate 6min duration, 2 year ARI.
2
mm/hr
From AR&R (2001) book 2 formulae B(3.1). 2
i6m = F2 ( 2 i 1hr )0.9
© Rail Corporation Issued December 2009
UNCONTROLLED WHEN PRINTED
Page 74 of 82 Version 1.2
RailCorp Engineering Manual — Geotechnical Track Drainage
TMC 421
50
Calculate 6min duration, 50 year ARI.
i 6min
=
mm/hr
From AR&R (2001) book 2 formulae B(3.2). 50
i6m = F50 ( 50 i 1hr )0.6
(f)
Determine the critical rainfall intensity Icr,50 for the critical duration tc and an ARI of 50 years. Method 1: Graphical method. Plot the points in e) on a Log-Pearson Type III Interpolation diagram (see Diagram 2.2) and join lines between these 2-year and 50-year ARI’s. Refer to AR&R (2001) Volume 1,Book 2. Method 2: Adopt AR&R Formulas that interpolate between rainfall durations. Determine modified intensity values (I1hr,50, I12hr,50, I72hr,50) using skew lines at the bottom of the graph. Plot these values as well as 50i6m on the Duration Interpolation Diagram 2.1 and read off the critical 50 year intensity, Icr,50. Refer to Section A.3 of AR&R (2001) book 2. Method 3: Utilise computer software (eg “IFD” or “Drains”) by entering values from e).
(g)
=
C10
=
mm/hr
Determine the 50 year runoff co-efficient C50. C10 - from previous (e) Geographical zone. From Figure 1.2 AR&R (2001) book 4.
zone
= zone B (for Sydney Metro area)
Determine Frequency factor (FF50). Using Formulas or interpolating values given in Table 1.1 AR&R (2001) book 4.
FF50
=
C50
=
Calculate C50 = C10 FF50
(h)
Icr,50
Calculate the 50-year peak flow rate Q50 utilising the Rational Method. This represents the amount of water that will flow on a catchment for the critical 50-year storm. F
Conversion factor for formulae F = 0.278 if A is in km
= 0.278
2
Q50 = F C50 Icr,50 A
Q50
=
m3/s
from AR&R (2001) book4 eq’n 1.1 (i)
Determine the required drain capacity To calculate I use Figures 2.18, 2.19, 2.20, 2.21 and equations 2.3, 2.4, 2.7 and 2.8 in AR&R (1977). QR = runoff quantity collected = Q50
QR
=
m3/s
QS = subsurface water intercepted
QS
=
m3/s
QC = watering entering from another system (eg separate drainage line)
QC
=
m3/s
QPF
=
m3/s
QPF = QR + QS + QC =
Note: this procedure determines the amount of water passing at a single point based on the original catchment area. If multiple catchment areas are incorporated into a system, then this process should be repeated for each catchment. Because of the repetitive and time-consuming nature of this procedure, it is recommended that such method be entered into a spreadsheet, or computer program. Alternatively, hydrology software incorporating AR&R methods may be a cost-effective method to use in preference.
© Rail Corporation Issued December 2009
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Page 75 of 82 Version 1.2
RailCorp Engineering Manual — Geotechnical
Track Drainage
TMC 421
10 10
§:
0.0
0.0
0.1
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Back to rable of Contents
HU~EAU
1.0
"" r· "
..."
N~ "
~
STANDARD DEVIATE ( YK) fOR AVERAGE RECURRENCE INTERVAL Y YRS FOR LOG · Pe:ARSON TYPE ll[ DISTRIBUTION
OF
METEOROLOGY
LOG • PEARSON TYPE Ill INTERPOLATION DIAGRAM FOR STANDARD AVERAGE RECURRENCE INTERVALS (ARI)
© Rail Corporation Issued December 2009
UNCONTROLLED WHEN PRINTED
DIAGRAM 2.2
Page 76 of 82
Version 1.2
RailCorp Engineering Manual — Geotechnical
Track Drainage
TMC 421
IIlO
800
lillO
600
SOil
500
100
100
llO
300
200
200
100
100
80
80
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IIJI
201
3IJI
IH
211
3H
611
1211
21ft
\$1
7a1
.3
DURATION (minutes: Mand hours: H)
Back t o Table of Contents
a
© Rail Corporation Issued December 2009
BUREAU OF
METEOROLOGY
DURATION INTERPOLATION DIAGRAM
UNCONTROLLED WHEN PRINTED
DIAGRAM 2.1
Page 77 of 82
Version 1.2
RailCorp Engineering Manual — Geotechnical Track Drainage
Appendix 5
© Rail Corporation Issued December 2009
TMC 421
Drawings: Typical Examples
UNCONTROLLED WHEN PRINTED
Page 78 of 82 Version 1.2
RailCorp Engineering Manual — Geotechnical
Track Drainage
TMC 421
r u,. ,.,.,
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sou: 1:15
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© Rail Corporation Issued December 2009
N/A
l/151 tWt IISD V151115HIISO
TOP 1)0-KJ ,., CASl JIQI II) tiRATE CAST fRQN IIJ liiRATl, ~POT
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UNCONTROLLED WHEN PRINTED
Page 79 of 82
Version 1.2
RailCorp Engineering Standard - Geotechnical
Appendix 6
ESC 420
Approved Track Drainage Products
Manufacturer ADS
Version: 2.0 Draft A Issue Date: May, 2009
Supplier
Type
Cubic Solutions High density polyethylene (HDPE)
© Rail Corporation 2009
Page 80 of 82
RailCorp Engineering Standard - Geotechnical
Version: 2.0 Draft A Issue Date: May, 2009
ESC 420
© Rail Corporation 2009
Page 81 of 82
RailCorp Engineering Standard - Geotechnical
Appendix 7
ESC 420
R Loading Configuration The ‘R’ vehicle is a rigid truck with the same configuration as the prime mover portion (first 3 axles) of the ‘T’ vehicle and the numerical portion is the vehicle’s weight in tonnes.
Standard
T44
Vehicle
4.9
9.8
9.8
9.8
Axle Loads (Tonnes)
1800
9.8
3700
1200
1200 Variable 3000-8000 To produce maximum loading effect
R20
Vehicle
Design Vehicle Configurations
Version: 2.0 Draft A Issue Date: May, 2009
© Rail Corporation 2009
Page 82 of 82
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