Design And Analysis Of Tunnel

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A MINI PROJECT ON ANALYSIS OF UNDERGROUND TUNNELS (According to practical principles)

Submitted in the partial fulfillment of the Requirements For the award of the degree of Bachelor of Technology In Civil Engineering By M. PRATHIGNYA (16281A0141) D. RASAGNA (17285A0104) P. VINEETH KUMAR (16281A0119) V. SRIKANTH (16281A0128) Department of Civil Engineering Kamala Institute of Technology and Science, Singapur

KAMALA INSTITUTE OF TECHNOLOGY AND SCIENCE SINGAPUR, KARIMNAGAR. DEPARTMENT OF CIVIL ENGINEERING

CERTIFICATE This is to certify that the industrial oriented mini project report entitled “ANALYSIS

OF UNDERGROUND TUNNELS

is a bonafied work carried out by

M. PRATHIGNYA (16281A0141) D. RASAGNA (17285A0104) P. VINEETH KUMAR (16281A0119) V. SRIKANTH (16281A0128) Submitted in the partial fulfillment of the requirement of award of Bachelor of Technology in Civil Engineering by JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY, Hyderabad (T.S.) during academic year 2016-2020.

Mr. Project guide & Asst prof.

Dr. MOHAMMAD ALI Prof. & Head of the Department

ACKNOWLEDGEMENT

We express thanks and gratitude to Dr. MOHAMMAD ALI Head of department Civil Engineering, KAMALA INSTITUTE OF TECHNOLOGY & SCIENCE , for her encouraging support in carrying out our project.

We are grateful to Sri. VenkataRamulu, Executive Engineer, I&CADD and

Sri.

V.VasanthRao, Deputy Executive Engineer, I&CADD for the permission to use all necessary material to complete our project. We are highly indebted to Sri. M. Sreenivas, Asst. Executive Engineer, I & CADD, of DR. B.R.AMBEDKAR PRANAHITHA CHEVELLA SUJALA SRAVANTHI PROJECT, Package-8, the executing agency MEIL-SEW-MYTASBHEL-CONSORTIUM for being our project guide as well as for providing necessary information regarding the project and helping us in completing our project successfully.

We are thankful to Sri. Ramesh Naik, Asst. Executive Engineer, I & CADD and other staff members for their co-operation. Special thanks to Sri. S. Konda Reddy (MEIL), for suggesting an excellent project to accomplish our higher goals.

Contents

PART - I Abstract

4

Introduction

5

Tunnel construction plan of package 8

7

PART - II 1. Geological and geotechnical survey

11

2. Design of tunnel

14

2.1. Tunnel layout

14

2.2. Geometry of tunnel

14

2.3. Tunnel supports

15

2.3.1. Need for tunnel supports

15

2.3.2. Estimation of design support systems

15

2.3.3. Design of tunnel support

19

2.4. Marking of tunnel layout 3. Excavation of tunnel

29 29

3.1. Factors to be considered while excavation

29

3.2. Process of excavation

31

3.3. Machinery used in construction of tunnels

36

3.4. Accidents and safety precautions

40

4. Problems encountered during construction and maintenance of tunnels

42

5. Factors to be considered for efficient tunnel construction

43

PART – III The Future

45

Conclusion

45

References

46

Abstract In this project, Scope and significance of Dr. B.R AMBEDKAR PRANAHITA CHEVELLA SUJALA SRAVANTHI LIFT IRRIGATION scheme is introduced. Brief note on overall investment and requirements of the project are given. Location and extension of package- 8 is provided with necessary details. Execution plan of package -8 is discussed in detail. Brief account on Geological and geotechnical investigations is given in this report. Rock load, rock mass quality index and other required properties are calculated and appropriate conclusions are interpreted. Tunnel supporting system is explained. Design and method of constructions of these supports for rock present at the site are worked out. Suitability of the drilling and blasting method and step wise description of this process of construction is elaborated. In this report, details of equipment used for various construction operations are discussed. Specifications of the equipment used in this package are provided. General problems encountered in construction of tunnels and different methods adopted in this package to overcome these problems are explained.

PART-I INTRODUCTION The Dr. B.R. AMBEDKAR PRANAHITA CHEVELLA SUJALA SRAVANTHI LIFT IRRIGATION SCHEME. is designed to link Pranahitha River at Tummidihetti village, Koutala (mdl) in

Adilabad district, to Chevella tank at Rangareddy district, which is

493metres(1617.45ft) higher than starting point, through a series of Tunnels, Pump houses and gravity canals. The Pranahitha - Chevella project comprises of 28 packages each package consists of series of tunnels, Lift system and gravity canals. This is being undergone to lift 160 TMC of water to a height of 493metres in 22 lifts and 7 Links, to envisage irrigation of about 1640000 Acres of Ayacut in 8 districts viz., Adilabad, Karimnagar, Nizamabad, Medak, Nalgonda, Warangal, Khammam and Rangareddy in Telangana region.

While the series of mammoth lift irrigation schemes taken up under Jalayagnam require over 8,600 MW of installed capacity to generate electricity needed to operate their massive pumps and motors to lift the water. Pranahita-Chevella is the major project of Jalayagnam projects, with a revised out lay of Rs. 40,300 crore, requiring 3375 MW of power & annual electricity of 7.5 billion KWhr with 530 meters average pumping head. Lengths of various components of this project including all the packages are: ➢

Total length of the system: 1055kms.



Length of the Gravity canal:849km



Length of Tunnel:206km

PROJECT MAP

The scheme envisages construction of barrage across Pranahitha River, a major tributary of Godavari river at Tummidihetti(v) in Adhilabad (D) and 160TMC of water from of Pranahitha River is proposed to be diverted to Sripada Yellampally project from where it is carried to command areas through lift schemes, Gravity canals, Tunnels, Modernization of tanks and reservoirs for irrigating total ayacut of 16.40 Lakhs Acres and providing drinking water facility to enrooted villages and also providing required water to industries in Hyderabad city. The Link-II from Sripada Yellampally Reservoir to Mid-Manair Reservoir works are made into 3 packages and named as Packages - 6, 7 & 8.

Tunnel construction plan of package 8: It’s a scheme of drawl and lifting of 114.26TMC of water from Rangampet village, Choppadandi(M) to Motevagu reservoir and carrying by a gravity canal to existing flood flow canal to feed Mid Manair reservoir with components such as Lined gravity canals, CM CD works, Lifts, Pressure mains and Lined tunnels. Total length of tunnel is 4133metres from the end of 7th package, i.e., after crossing Kakatiya canal to underground surge pool of 8th package. This tunnel comprises of D shaped twin tunnels, one with 10m diameter and other with 7.5m diameter. The size of underground Surge pool is 350m X 20m X 54m and size of underground Pump house is 210mX 25m X 64 are designed. 5 draft tube tunnels of 50 metres length connect surge pool to pump house. The power requirement of this package is 722MW. 5 Francis turbines each with 121.5 MW is planned to be installed to lift 114.24 TMC of water to head of 109.10 metres. From pump house horizontal shaft of length 30 metres and vertical shaft of length 150 metres, having 5m diameter finished pressure mains are provided to join 50 metres long delivery cistern which delivers water to gravity canal which is 4060kms long to join Motevagu reservoir.

CAD DRAWING

Audit tunnels: The audit tunnel is a temporary tunnel for the main tunnels,there is no need for any permanent final lining. Here adit tunnel constructed at Kistampalli(V). The size of adit tunnel is 8.0m D-shaped tunnel,1609.0m long with 1in 12 slope.It joins at 3.9km(Cumulative Ch:14.438Km from Medaram reservoir) of main tunnel, clearly shown in plan The overburden at juction tunnel is approxiatly 110.0m An Access tunnel to surge pool is provided at 804m of main adit, the size of access tunnel 8.3m D-shaped tunnel,202m long with 1 in 12 slope to facilitate execution of Surge pool and Pump House simultaneously.

The clear width of rock ledge between pump house and surge pool is about 58.5metres. An approach tunnel of 9 m diameter is excavated at 0.135 kms of access tunnel to the surge pool for length of 210 metres to join service bay of pump house for transporting all electrical and mechanical works for pumping arrangements. In between surge pool and pump house two ventilation tunnels with 9m D-shaped tunnels at 65m and 115m from the centre of main twin tunnels are provided. The crown portion of pump house and surge pool 10x10 metres pilot tunnels is completed.

. Drilling cavity for construction of vertical shaft at the end of pump house

For opening the vertical shaft of 9metresdiameter the cavity has been formed at invert level of +234.500 of heading of pump house to create access to the pump house through lift and stair case along with electrical cable. As per the design the systematic rock bolting 25mm diameter TOR steel for length of 6metres at 1.5 metres c/c is being done for the final excavated areas of surge pool and pump house cavities. After rock bolting 100mm thick SFRS (Shotcrete Fibre Reinforced Steel) will be done for final protection.

The plan of this package is based on the results of geological and geotechnical survey. Then the supports for different rock strata are designed. Now, process of excavation is started considering the safety precautions and various problems encountered.

PART – II

1.

Geological and geotechnical survey Thorough geologic analysis is essential in order to assess the relative risks of different

locations and to reduce the uncertainties of ground and water conditions at the location chosen. Key factors to be considered during geological survey include: •

Soil and rock types.



Size of rock block between joints.



Weak beds and zones: Faults, shear zones and altered areas weakened by weathering or thermal action.



Groundwater: Flow pattern and pressure.



Special hazards: Heat, gas, and earthquake risk.

For mountain regions, to assess geological conditions, the large cost and long time required for deep borings generally limit their number. Aerial and surface surveys, plus welllogging and geophysical techniques can be used as best alternatives. Depending on the changes in design and in construction methods, continuous exploration ahead of the tunnel face is done by mining a pilot bore ahead, in older tunnels. Now this is done by drilling bore holes. Japanese engineers have pioneered methods for pre-locating troublesome rock and water conditions Geological and geotechnical investigation carried out give the data about: 1) Nature of the sub surface strata (geological data) in tunnel location 2) Ground water availability and seepage conditions 3) Engineering properties of rock strata 4) Seismic data of the region Geological conditions at tunnel location: The tunnels are excavated at chainage of 3.9 km near Venkataraopalli in Karimnagar district, Andhra Pradesh. The soil and the rocks conditions at this location are defined tectonic elements containing fairly good record of the Archaean, the Middle-Upper Proterozoic and Gondwana strata. The Karimnagar Granulite Belt (KGB) and the Bopalapatnam Granulite Belt (BGB) occur along both flanks of the Pranahita – Godavari (PG) rift basin. So, large percentage of the rock present at the site is hard, very competent granite rock, comprising of grey and pink massive granites with the essence of quartz and feldspar minerals.

Field work done for geological data: For the recording of geological data in package -8, the BORE LOG data and ELECTRO-RESISTIVITYMETHOD is used. Data by bore logs: To know the various engineering properties of the rock 6 bore holes are drilled in alignment of the proposed tunnels. Samples are collected for testing.

BOREHOLE

CHAINAGE (km)

DEPTH (m)

BH6

0.65

100

BH1

0.88

102

BH7

1.20

104

BH2

2.20

109

BH3

3.10

120.2

BH4

3.94

130.1

From BH6: Sample collected range: 89 to 99m Uni-axial compressive strength, MPa 1) Dry strength = 68 (average) 2) wet strength = 67 (average) Specific gravity = 2.70

From BH1: Sample collected range: 87 to 97m Uni- axial compressive strength, MPa 1) Dry strength = 61 (average) 2) wet strength = 56 (average) Specific gravity = 2.67

From BH7: Sample collected range: 89 to 99m Uni- axial compressive strength, MPa 1) Dry strength = 73 (average) 2) wet strength = 70 (average)

Specific gravity = 2.74

From BH2: Sample collected range: 96 to 101m Uni- axial compressive strength, MPa 1) Dry strength = 72 (average) 2) wet strength = 73 (average) Specific gravity = 2.715

From BH3: Sample collected range: 104 to 114m Uni- axial compressive strength, MPa 1) Dry strength = 83.5 (average) 2) wet strength = 84 (average) Specific gravity = 2.712

From BH4: Sample collected range: 110 to 125m Uni- axial compressive strength, MPa 1) Dry strength = 72 (average) 2) wet strength = 73 (average) Specific gravity = 2.691 Availability of ground water from six boreholes: nil Poison’s ratio: 0.3 Conditions of joints: rough Jr=

joint roughness factor

=4

Jw= joint water reduction factor

=3

Jn= joint structure number

=1

Ja= joint alteration number

=1

SRF = stress reduction factor

= 2.5

Therefore, from this geological data, the rock mass quality is calculated and the rock quality is known. By the electro resistivity method other data like the depth of the rock cover on the tunnel is known.

Depth of rock cover = 80m (approx.)

Reference: In package 8, the geological investigation i.e., the bore log data, is carried out by contractor Ashwini Kumar Roy and geotechnical investigation i.e., the ERM is carried out by Sri Sai Siva Ganga Geo- Technics.

2.

Design of tunnel

2.1.

Tunnel layout Tunnel design is made based on the obligatory points. These are the points through

which either tunnel must pass or must not. Tunnel is designed such that it does not disturb residences other main pipe lines. It is also checked if it fills all the possible nearer tanks. This also depends on the borehole data of the underground rock strata. Tunnel is designed such that it passes through the competent rock for maximum length. The project site mainly passes through the Karimnagar Granulite Belt (KGB). It mainly consists of grey granite and pink granite. Till now Very few weak strata are encountered while constructing adit and access tunnels. Required ground and rock supports are given for these areas.

2.2.

Geometry of tunnel Tunnel shape is very important in determining stand-up time. The force from gravity is

straight down on a tunnel, so if the tunnel is wider than it is high it will have a harder time supporting itself, decreasing its stand-up time. If a tunnel height is greater than its width, the stand-up time will increase, making the project easier. The hardest shape to support itself is a square or rectangular tunnel. The forces have a harder time being redirected around the tunnel making it extremely hard to support itself. This of course all depends on the material of the ground. Circular tunnel is best shape in terms of capacity but is preferred when TBM is used. In drilling and blasting method D shaped tunnel is preferred as this also gives greater working area and hydraulic losses are also less in this case. D shaped tunnels prevent the slumping of wet concrete due to their flatter invert.

2.3.

Tunnel supports

2.3.1. Need for tunnel supports

As the tunnel is incrementally excavated the roof and sides of the tunnel need to be supported to stop the rock falling into the excavation. The tunnel requires support for the following reasons: 1) Due to the presence of different classes of rocks in tunnel

2) Due to presence of loose strata at crown 3) Due to increase in overburden pressure at intersections of tunnel 4) Due to the seismicity In our package -8, the tunnel mainly passes through the very competent granite rock and the possibility of encountering loose strata is very rare. Large percentage of rock falls under class1 rock classification so no supports are required. But at some locations of tunnel the supports are required due to the tendency of excavated rock to drop off from the roof of the tunnel.

2.3.2. Estimation of required support systems The tunnel support system design is done as per guidelines by IS codes.

ROCK LOAD: Rock load refers to the height of the rock mass which tends to drop out of the roof. The rock load is to be estimated in order to know the pressure acting upon the supports. The rock load depends upon the stress conditions. The stress condition varies before and after the excavation. The primary stress condition before excavation is less as no factors are considered, and the stress is mainly due to earth pressure, but there is large change in secondary stress conditions due to factors caused by after excavation such as: •

Size and shape of excavation



Depth of excavation



Dislocations in strike and dip in rock formations Rock load at depths less than or equal to 1.5(B+Ht), is considered equal to its depth.

It the depth at which rock load is to be calculated is greater than 1.5(B+Ht) it is calculated by Fenneis ellipse or Russian methods. ESTIMATION OF ROCK LOAD: FOR RIGHT TUNNEL: Width of tunnel opening = B = 12.05 m Height of tunnel opening = Ht= 12.05 m 1.5(B+Ht) = 36.15 m

Rock load at depth = 80 m Therefore Rock load at depth > 1.5(B+Ht) By Terzaghi’s method

Hp Min

0

0

Max

0

0.25B = 3.0125 Average = 1.51

Rock load calculated = 1.51 m

FOR LEFT TUNNEL: Width of tunnel opening = B = 9.02 m Height of tunnel opening = Ht= 9.02 m 1.5(B+Ht) = 27.06 m Rock load at depth = 80 m Therefore Rock load at depth > 1.5(B+Ht) By Terzaghi’s method

Hp Min Max

0 0

0 0.25B = 2.25 Avg= 1.12

Rock load calculated = 1.12 m This is under the limits defined by I.S. code.

Estimation of Rock mass quality and Roof support pressure: The support system in tunnel is designed based on the manual – “Planning and Design of Hydraulic Power by Central Board of Irrigation and Power”. The estimation of rock mass quality and roof pressure can be calculated by Bieniaswski (C.S.I.R) method

Barton’s (N.G.I) method In our package we are using the Barton’s method. The steps to be followed are: 1)

Calculation of rock mass quality index Q

By formula; Q = (RQD JrJw)/ (Jn. Ja. SRF) Where, RQD = Rock quality designation Jr= joint roughness factor Jw= joint water reduction factor Jn= joint structure number Ja= joint alteration number SRF = stress reduction factor

2)

Then calculate De;

De = excavation span, diameter (or) height / ESR Where, De = equivalent dimension ESR = excavation support ratio

3)

Roof support pressure is to be calculated

Proof = [2. (Q)-1/3]/ Jr Where, Proof = Permanent roof support pressure Jr= Joint roughness factor Q

=Rock mass quality

Calculations for right tunnel: RQD = 82.5 Jr= 4 Jw= 3 Jn = 1 J a= 1 SRF = 2.5 Q

= 24.75 (calculated)

Excavated diameter = 11.3m ESR

= 1.6

De

= 7.06 (calculated)

Proof = 0.23

For left tunnel: RQD = 82.5 Jr

=4

Jw

=3

Jn

=1

Ja

=1

SRF

= 2.5

Q

= 24.75 (calculated)

Excavated diameter = 8.75m ESR

= 1.6

De

= 5.4 (calculated)

Proof

= 0.23

Therefore, the rock mass quality = 24.75 De De

= 7.06 (for RT)

= 5.4 (for LT)

So as per manual on planning and design of hydraulic tunnels published by central board of irrigation and power “NO SUPPORT REQUIRED”

ESTIMTION OF PERRMISSIBLE UNSUPPORTED SPAN MAXIMUM UNSUPPORTED SPAN: - It can be defined as the length of span which could resist the drop off from roof of tunnel. If the maximum unsupported span is greater than actual excavation span, then design is safe and no support is required. But the value of maximum unsupported span is related to the rock man quality (Q) which we calculated earlier. Relation: - L= 2*ESR*Q0.4

FOR RIGHT TUNNEL: Q

= 24.75

ESR = 1.6 L

= 11.55(calculated)

Actual excavation span = 12.05 m

Therefore, maximum span > excavation span No support required

FOR LEFT TUNNEL: Q

= 24.75

ESR = 1.6 L

= 11.55(calculated)

Actual excavation span = 9.02 m Therefore, maximum span > excavation span Hence, “NO SUPPORT REQUIRED”.

Thus, according to estimation of rock mass Quality, roof pressure and permissible unsupported span, the design is safe and no support is required.

SEISMICITY: The tunnel location falls under the area of non-active seismic zone. It comes under zone-2 and zone-3 which encounters the low seismic hazards. Hence seismic forces are not considered in the package 8. Therefore, on account of all the estimations of rock load, rock mass quality, permissible unsupported span and even seismicity, are under the safe limit and support design is not required for the complete tunnel. Thus, a simple support design can be adopted at some locations to overcome the problem of loose strata.

2.3.3. Design of tunnel supports The New Austrian Tunnelling Method (NATM) was developed in the 1960s, and is the best known of a number of engineering solutions. By special monitoring the NATM method is very flexible, even at surprising changes of the geo-mechanical rock consistency during the tunnelling work. The main idea of this method is to use the geological stress of the surrounding rock mass to stabilize the tunnel itself, by allowing a measured relaxation and stress reassignment into the surrounding rock to prevent full loads becoming imposed on the introduced support measures. Based on geotechnical measurements, an optimal cross section is computed.

The excavation is immediately protected by a layer of sprayed concrete, commonly referred to as shotcrete, after excavation. Other support measures could include steel arches, rock bolts and mesh. Tunnel supports are classified as tunnel portal, initial supports and final supports. ➢

Tunnel portal:

The opening where the tunnels come out of the ground is called a tunnel portal. As a normal practice whenever the tunnel operation is to be started, a portal has to be constructed at the working face. hence an approach road has to be constructed first to reach the working face. The rock at the working face is highly weathered and drops as it is loose. So, this dropped rock is to be mucked first and portal has to be constructed.

Design of tunnel portal: For the package 8, the tunnel portals are not necessary for the main tunnel as the entry and exit of twin tunnels are at surge pool of package 7 and surge pool of package 8 respectively. Therefore, the only requirement of tunnel portal is at the audit tunnel due to its geological conditions. As the rock in the tunnel location is granite there no need of constructing heavy portals. The audit tunnel doesn’t require the permanent portals as they are used as a passage to construct the main tunnels. Vertical and horizontal lines passing through the center of designed audit tunnel are first marked. With reference to the center lines the shape of the tunnel face is to be marked as done in the excavation method and the portal is to be constructed around the periphery of audit tunnel. After the reinforcement is done, the portal should be shotcrete with 30mm thickness. Tunnel Portal Equipment used for construction tunnel portals: Drill Jumbo, Dump Loader, rear Dumper, Crawler drill and Batching plant for concreting ➢

Initial tunnel support:

This support is provided immediately after the excavation to hold up the loose strata. It is used so that the rock is held in position temporarily or is may be permanent. Earlier, timber sections

were used as initial support. But due to advancement in construction, it is replaced to steel structures. These provision of steel structures as a support positions the loose rock at opening. As the quality of the rock increases, the installation of the initial support decreases. The initial support can be of following types. o Steel support system with shotcrete Shotcrete is used in combination with wire mesh.Shotcrete is concrete (or sometimes mortar) conveyed through a hose and pneumatically projected at high velocity onto a surface, as a construction technique. Shotcrete undergoes placement and compaction at the same time due to the force with which it is projected from the nozzle. It can be impacted onto any type or shape of surface, including vertical or overhead areas.

Shotcrete layer with wire mesh Shotcrete refers to the ‘sprayed concrete’. It is an effective solution when used in combination with steel reinforcement and wire mesh. As the rock in package-8 is competent granite rock, it is not necessary for complete shotcreting of tunnel. In this case, rock bolts are considered as the steel fibers and shotcrete. It could act as the permanent support. shotcrete details: Rock bolt spacing =1.5m Thickness of shotcrete =30mm

o

Steel ribs reinforcement

Steel ribs are used during heading and benching to prevent loose rock strata from dropping down from roof as well as sides of tunnel during construction. They are also used in order to stabilize the rock dislocations. The installing support should be designed by considering the maximum probable load and bridge action period of rock. The bridge action period of rock varies from strata to strata. As in package 8, the rock is granite hence the bridge action period is more and also probable load is yet to be calculated. After the installation of steel ribs support along walls and crown of tunnel it should be suitably back packed with concrete by back filling and grouting techniques.

Support - Steel rib reinforcement In package8, we are using reinforcement of type-RIB-WALLPLATE AND POST. FOR RIGHT TUNNEL: Steel ribs - ISMB 200X100X10 @25.4 kg/m Double beam wall plate – ISMC 200X75X10 @22.1 kg/m (2 no’s) Proposed vertical post under rib ISMB 200X100X10 @25.4 kg/m a)

Baseplate

b)

Diaphragm plate

Splice plates (4 no’s) two on each rib Length of the plate= 400mm Width of the plate

= 160 mm

Thickness of the plate = 10 mm Mild steel tie rods staggered Diameter of rods

= 16mm

Spacing

= 600mm c/c

RCC precast lagging

– 980X200X75 -M25 grade

Backfilling behind lagging –M20 grade Contact grouting

–M20 grade

FOR LEFT TUNNEL: Steel ribs - ISMB 150X80X10 @14.9 kg/m Double beam wall plate – ISMC 200X75X10 @22.1 kg/m (2 no’s) Proposed vertical post under rib ISMB 150X80X10 @14.9 kg/m a)

Baseplate

b)

Diaphragm plate

Splice plates (4 no’s) two on each rib Length of the plate

= 400mm

Width of the plate

= 110mm

Thickness of the plate = 10 mm Mild steel tie rods staggered Diameter of rods

= 16mm

Spacing

= 600mm c/c

RCC precast lagging

– 1180X200X75 -M25 grade

Backfilling behind lagging

–M20 grade

Contact grouting

–M20 grade

o

Rock bolting The use of rock bolts can be dated back to Roman Empire and it was commonly

believed that rock bolts pin surface rock (bedded rock strata or individual rocks) to more stable rock. Rock bolts are pretensioned bolts which consist of a base bearing plate at its bottom and a long cylindrical rod attached to it. It is drilled into the crown of tunnel by making a hole. With the insertion of rock bolt into rock slope, it increases the rock mass’s stiffness and strength with respect to shear and tensile loads. Axial force in rock bolts consist of a force component normal to joint plane which contributes frictional resistance, and a force component parallel to joint plane which contributes to dowel action.

Rock bolts at intersection

Rock bolts are tensioned once the anchorage is attained to actively set up a compressive force into the surrounding rock. This axial force increases the shear capacity and is generated by pre-tensioning of the bolt. The system requires a bond length to enable the bolt to be tensioned. In essence, rock bolts start to support the rock as soon as they are tensioned and the rock does not have time to start to move before the rock bolt becomes effective.

Installation of rock bolt

The rock bolting is referred to as the ground reinforcement as it supports the rock load and helps the different strata of rock to improve its strength. Rock bolting follows the principle of fastening the loose rock at the surface to the solid rods above by the means of anchor bolts. Apart from supporting the loose rock it also assist it to act as load carrying element.

These are inserted in different positions depending on the alignment of the joints. Inclined rock bolts help to stiffen shear and results in an increase in shear strength at smaller displacements. Rock bolts perpendicular to shear planes provides the lowest shear resistance. The optimal inclination of rock bolt is 30o to 60o based on past experimental works. The space between the bolts shall be chosen in accordance with the length and diameter of the bolt.

For greater support, the rock bolts are inserted with epoxy resin cartridges which flow out between the bolt and rock strata and settle over to give a rigid support. The gaps between the hole and bolt are to be filled or concreted to avoid the problem of corrosion.

Dimensions of Rock Bolt: Dimensions of bearing plate=150X150X12 Diameter of bolt=25mm Capacity-12ton proven capacity Hole diameter -32 to 38mm Length of bolt-(RT-4m, LT-3.5m) Spacing of rock bolts-1.5m

ADVANTAGES OF ROCK BOLTING: o

It is economical.

o

Installation process is simple.

o

Time consumption is less.

o

Backfilling

It is the process of filling voids that occur during the excavation of tunnel or voids that exist between excavated rock and initial support. Depending on the final liner used backfilling material and the equipment varies. It also depends on the geology of the surrounding rock and structural and operational requirement of the tunnel. All the backfilling material are essentially composed of neat cement, sanded cement, conventional concrete, flowable fill, cellular concrete. When implementing a backfilling program size shape and extent of the void is generally known prior to the backfilling operation. •

Backfilling reduces permeability of final lining.



It reduces rock deformation around tunnel.



It puts final lining in complete contact with the roof and thereby distributing the load equally.

• o

It Reduces groundwater flow around tunnel

Grouting

Grouting means filling of gaps that are unintentionally created during the excavation of tunnel and lining methods used. The size, shape and extent of void are generally unknown prior to the starting of the grouting operation. Grouting is done to fill •

Voids that may exist between excavated surface and the previously placed backfill



Between backfill and initial support



Between backfill and final lining

These voids generally occur due to Shrinkage or flow blockage of backfill.



Final supports

o

Lining

Selecting efficient lining method is very important for tunnel safety and serviceability. Selection of lining methods is controlled by technical and non-technical factors. Technical

factors represent the project conditions such as ground condition and tunnel shape, etc. Nontechnical factors are cost and time. Tunnels for water transport need smooth lining to prevent the losses due to formation of eddies and air pockets which would reduce the capacity of the tunnels. Groundwater flow into the tunnel is directly relational to the groundwater pressure around the tunnel. Ground water pressure on the lining depends on groundwater table height and relative permeability of the ground. Groundwater inflow rate represents groundwater pressure and ground permeability, the amount of groundwater that the lining method will resist should be taken into consideration during selecting the lining method. In large tunnels batching or mixing plant is necessary to manufacture concrete for lining. The concrete may be mixed in standard batching and mixing plant outside the tunnel and this mixed concrete is taken to the site of placement or the aggregates may be batched and mixed dry outside and mixed with water inside the tunnel. It is advisable to add cement inside the tunnel to avoid setting. Except for small tunnels, generally concrete pumps are inside the tunnel near the site of lining.

Different types of linings are: o

Precast concrete segments

o

Steel segments

o

Reinforced concrete segments

o

Pipe in tunnel

o

Shotcrete lining

o

No final lining

For this package shotcrete lining is suggested based on the rock type. No lining is done to the adit canal which would be closed before the main tunnels starts conveying water.

Different levels of lining designed based on rock class is tabulated below.

Type of rock

Class I

Required lining

M20 plain cement concrete lining of 500mm thick is laid.

In additional to M20 plain cement concrete Class II

lining of 500mm thick 25mm spot bolts of 4metres length is provided.

30mm shotcrete is used for crown in Class III

additional to 500mm thick M20 PCC lining in and 25mm spot bolts with 4metres length.

500mm thick M20 RCC lining. 25mm spot bolts with 4metres length. 50 mm shotcrete in crown where required. Class IV

RCC m25 lagging ISMB 200x100 @1000c/c ISMC 200x75Anchor rods Tie rods M20 backfill concrete m20 base concrete

500mm thick M20 RCC lining. 25mm spot bolts with 4metres length. 100 mm shotcrete in crown where required. Class V

RCC m25 lagging ISMB 200x100 @1000c/c ISMC 200x75Anchor rods Tie rods M20 backfill concrete m20 base concrete

2.4.

Marking of tunnel layout



Marking on surface

Total station is used to mark coordinates along the path which are already specified in design. These coordinates are marked on surface. A point for every 1metres is noted. ➢

Marking underground

These coordinates are fed in the total station under particular job. These coordinates are adjusted by keeping the x and y coordinates constant and varying z coordinate based on the depth of the tunnel. Now the required points are marked by laser beam.

Marking coordinates using total station

3.

excavation of tunnel

3.1.

Factors to be considered while excavating tunnels



Prevention of entry of rain water and seepage water:

Open excavation should be started at a point which is on higher level than the surroundings. But this depends on the availability of the ground. Seepage water and Rain water in the tunnel shall be pumped out through ➢

Pipes along the adit tunnel.



Vertical pumping though bore holes.

This shall be done continuously, as entry of water in the tunnel poses difficulties for construction.



Ventilation: The ventilation is required to remove polluted air, gases and smoke produced by

explosives, dust formed by the disintegration of rock, exhaust gases from the diesel operated equipment like locomotives, dumpers, trucks, shovels, etc., and also to ensure temperatures of not more 29° C at the working place. Mechanical ventilation shall be adopted where necessary to force the air in or exhaust the air out from the working face to the portal through a pipe. The concentration of various gases in atmosphere inside the tunnel by volume shall be as follows: o

Oxygen -not less than 19.5 percent.

o

Carbon monoxide -not more than 0.005 percent.

o

Carbon dioxide -not more than 0.5 percent.

o

Nitrogen fumes- not more than 0.0005 percent.

o

Methane- not more than 0.5 percent at any place inside the tunnel.

o

Hydrogen sulphide- not more than 0.001 percent.

o

Aldehyde- as formaldehyde not more than 0.001 percent.

Volume of Air Required: The volume of air required shall depend on the following: o

Length of heading

o

Size of tunnel

o

Type and number of explosives used

o

Frequency of blasting

o

Temperature and humidity

In tunnel work 4.25 m3 of air/min/man is usually considered the minimum requirement. In addition to this 2.00 m3 of air/ min shall be supplied for such brake horsepower of diesel locomotive or other diesel engine used in the tunnel. Where the temperature is high or heavy blasting is resorted to suitably augmented volume of air shall be provided. •

Lighting:

Adequate lighting shall be provided at the face and at any other point where work is in progress and at equipment installations. A minimum of 50 lux shall be provided at tunnel and shaft

headings during drilling, mucking and scaling. The lighting in general in any area inside the tunnel or outside an approach road, etc. shall not be less than 10 lux. Emergency lights (battery operated) shall be installed at the working faces and at intervals along the tunnel to help escape of workmen in case of accidents. All supervisors and gang-mates shall be provided with cap lamps or hand torches. It shall be ensured that at least one cap lamp or hand torch is provided for every batch of 10 people. Any obstruction, such as drill carriages, other jumbos and drilling and mucking zones in the tunnel shall be well lighted.

3.2.

Process of excavation of tunnels For this project the drill-and-blast method is well suited. A drilling boomer is used to

drill a predetermined pattern of holes in the rock along the tunnel's path. Carefully planned charges of dynamite are inserted in the drilled holes. The charges are detonated in a sequence designed to break away material from the tunnel's path without unduly damaging the surrounding rock Workers generally use two basic techniques to advance a tunnel. In the full-face method, they excavate the entire diameter of the tunnel at the same time. This is most suitable for tunnels passing through strong ground or for building smaller tunnels. The second technique is the top-heading-and-bench method. In this technique, workers dig a smaller tunnel known as a heading. Once the top heading has advanced some distance into the rock, workers begin excavating immediately below the floor of the top heading; this is a bench. One advantage of the top-heading-and-bench method is that engineers can use the heading tunnel to gauge the stability of the rock before moving forward with the project. Then they repeat the process, which advances the tunnel slowly through the rock. In the present package heading and benching method is used. After drilling and blasting the rock, air is circulated through the blast area to remove explosion gases and dust. Rubble dislodged by the blast is hauled away. Pneumatic drills and hand tools are used to smooth the surface of the blasted section and remove loose pieces of rock. This Process is discussed step wise in this section.

Excavation cycle ➢

Drilling Holes are drilled by marking coordinates using Total station. Holes are of 40mm

diameter with depth lesser than the opening of the tunnel. Centre to centre spacing of 0.6 to 1metres is maintained between the holes. Lead line of holes, known as cut holes, is drilled in the same pattern of the shape of tunnel. Particular interval is maintained between two lead lines. In this interval easer holes are drilled maintaining spacing within the range. Outer lead line is drilled as contour holes. Holes are drilled by pusher legs and jack hammers manually or drilling jumbo or drilling boomers are used. This machinery is discussed in detail under 3.3.

Types of holes and Pattern of drilling Holes are classified into three categories. o

Cut holes: These holes shall be drilled in the centre of the cross section of the tunnel to

excavated converging towards the centre of the face to produce an initial cone or wedge. The holes shall be 150 to 300mm deeper than other holes. o

Easer holes: These holes shall be drilled to blast the area around the cone or wedge

created by the cut holes and thereby reducing the burden on other holes. Charge in these holes shall be less than that in cut holes. Easer holes shall be drilled around the cut holes. o

Trimmer or contour holes: these holes shall be drilled along the periphery of the

tunnel to give the excavated section a required shape. These holes shall carry relatively less charge to reduce over breaks. ➢

Loading and Blasting: Blast should be such that there is more rock fragmentation and less vibration level. This

depends on size, depth and spacing of drilled holes. Before blasting high pressure, air jet is blown into holes to remove loose rock and water. Only such explosives that produce less than 4530 ml of poisonous gas (carbon monoxide and hydrogen sulphide) per 3x20 cm cartridge shall be used for underground blasting work. Cartridges are available in 25 to 63mm diameter and length of 100mm to 300mm. Just before loading is started each hole shall be blown out with a high- pressure air jet to remove loose cuttings and water. In the process of charging no material other than clay sticks 25 mm diameter and 10 cm long shall be used for blinding and sealing the holes after charging the same. Generally, cartridges are kept 5mm less than the diameter of hole. Drilled holes are cleaned and blasting material is packed by workers. After material is placed it is covered with clay and sand and tamped. Next, workers evacuate the tunnel and electric power, light and other circuits in the vicinity within 70m of the loading points shall be switched off after charging the explosive and before the blasting operation starts. Power supply is to be switched on only after the blasted area has been properly inspected by the blasting foreman for misfires. All tracks, air lines and vent pipes shall be kept properly grounded. Immediately after a blast has been fired, the firing line shall be disconnected from the blasting machine or other source of power. When at least 5 minutes have passed after the blast was fired, a careful inspection of the face shall be made by the blaster to determine if all charges have been exploded. Electric blasting misfires shall not be examined for at least 15 minutes

after failure to explode. Other persons shall not be allowed to return to the area of blast until an 'ALL CLEAR' signal is given by the blasting foreman. All wires shall be carefully traced and search is made for any exploded cartridge by the Man-in-charge of the blasting operation. Sufficient time shall be given for the fumes to

clear before permitting the labour to work for scaling and mucking operations. Charging blasting material in drill holes

Every hole is not filled with blasting material. These holes help in forming fissures and weakening the rock with fewer vibrations. Blasting sequence is planned such that there is a delay of fraction of seconds within a blast to facilitate the loosening of rock and effective blasting. A good detonation blasts up to 90% of depth of hole. ➢

Ventilation

In this package ventilation is provided using air vents and ventilation tunnels. Tunnel ventilation is provided according to I.S codes. Air ducts can be operated in two ways. Fresh air can be pumped through the duct and the exhaust air travels back along the tunnel.

In another method duct suck out the exhaust air creating low pressure and thus fresh air from outside rushes through the tunnel to low pressure area. This creates better environment than the first one. In this package air ducts suck the fresh air forcing the exhaust air out through the tunnel. ➢

Scaling After vacuuming out the noxious fumes created during the explosion, workers can enter

the tunnel and start scaling operation. Blasting may not blow the required amount of rock. Few rocks may not be weakened enough to fall off. This is cleared by scaling off the loosened rock. Here scaling is done by excavators with Hydraulic hammers. ➢

Mucking

Removal of material after blasting is called mucking. This material is loaded into dumpers, dumpers or rail carts and is dumped outside the tunnel. Hauling roads should be provided from tunnel month to dumping site. The slope in audit tunnel and open excavation should not be greater than 1 in 12 as this reduces the efficiency of dumpers and life of machinery is considerably reduced. In this project, dumpers are used for mucking and slope of 1 in 12 is maintained in audit tunnel. ➢

Installation of supports

Supports are generally installed in following cases o

When the opening of the tunnel is greater than 10 metres

o

At tunnel junctions

o

Where loose or fault rock is encountered

o

When rocks are of different strata

Types of supports for different positions and different classes of rocks are discussed in detail in previous section. ➢

Lining

Shotcrete with wire mesh is used for tunnel portal. For most of the tunnel class I and II rock is encountered so nominal PCC and RCC lining with spot bolts are provided. Lining details for different types of rocks are designed in earlier section.

3.3.

Machinery used in construction of tunnel



Drilling boomers: Drilling Operation

Tunnelling through hard rock almost always involves blasting. Workers use a scaffold, called a boomer, to place explosives quickly and safely. The boomer moves to the face of the tunnel, and drills mounted to the boomer make several holes in the rock. The depth of the holes can vary depending on the type of rock, but a typical hole is about 3 meters deep and only a few centimetres diameter. In this project we use four computerized double boom drilling boomers. Drilling plans are saved in computer precise position and navigation is located by laser beam. Excavated profiles can be scanned for guiding next drilling and blasting.

Double Boom ATLAS COPCO Drilling Boomer

Computerised boomer with drill plan stored



Hydraulic Hammers: Scaling Operation

Nowadays dozens of various corporations throughout the world manufacture a great number of hydraulic hammers models, adaptable for installation on construction machines, such as excavators, lift trucks, manipulating equipment etc. in capacity of the removable attachment. The hydraulic hammers designed to break up various hard constructions and materials.

Hydraulic hammer ➢ Loaders1 2 loaders are being used in this package. Volvo L 180F and CAT 120(caterpillar INC) are used. Details of these loaders are specified below:

Volvo L 180F: Volvo L180F has the power and maneuverability needed to take on and quickly handle demanding applications in log handling, hard bank, and rock.

Volvo L 180F

Components of Volvo L 180F: General purpose bucket with Flat floor, this also helps for maintaining a clean and level work area. Rock bucket with side dump Heavy duty, wear resistant bucket for primary loading of shot rock with side dumping and for tunneling applications. Light material bucket –to carry refuse Grading bucket- For topsoil stripping, small scale dozing, landscaping and levelling. Block handling - Heavy duty forks, designed for lifting and moving blocks in quarry applications. Block handling - Clearing rake for moving objects and clearing debris. Volvo Construction Equipment also provides a wide range of Teeth and adapters for fewer worries and higher profitability.

Excavators: Excavators are heavy construction equipment consisting of a boom, stick, bucket and cab on a rotating platform (known as the "house"). The house sits atop an undercarriage with tracks or wheels. In this package cat 200 by caterpillar INC and volvo210 is being used.

Cat 200: Cat hydraulic excavators are known for swing torque, hydraulic power, controllability, faster cycle times, reliability, lower owning & operating costs, and the best tons per hour productivity in the industry.

Excavator Volvo 210: Components

Specifications

Engine

Volvo D6E

Breakout force

130,4 KN

Bucket capacity

0,92 m3

Max. digging reach

9,9 m

Max. digging depth

6,7 m

Lifting capacity along undercarriage

7,0 t

... at reach / height

6,0 / 1,5 m

Operating weight

20,4-23,7



Dump trucks: Mucking

A dump truck is a vehicle designed for carrying bulk material, often on building sites. A dump truck has its cab in front of the load. The skip can tip to dump the load; this is where the name "dump truck" comes from. They are normally diesel powered. A towing eye is fitted for secondary use as a site tractor Early dump trucks had a payload of about a ton and were 2-wheel drive, driving on the front axle and steered at the back wheels. The single cylinder diesel engine (sometimes made by Lister) was started by hand cranking. The steering wheel turned the back wheels, not front. Having neither electrics nor hydraulics there was not much to go wrong. The skip was secured by a catch by the driver's feet. When the catch is released, the skip tips under the weight of its contents at pivot points below, and after being emptied is raised by hand. Modern dump trucks have payloads of up to 10 tonnes (11 short tons; 9.8 long tons) and usually steer by articulating at the middle of the chassis (pivot steering). They have multicylinder diesel engines, some turbocharged, electric start and hydraulics for tipping and steering and are more expensive to make and operate. 18 trucks are used for the project. Asian Motor Wagons supplies this machinery to the project. We use AMW2523. Specifications of this model are listed below.



A 6x4ft Dump truck.



Loading capacity of 25-Ton.



Comes in outer structural frame with built cabin.



Used for carrying rocks, iron ores, coal

Dumper-AMW 2523

3.4.

Accidents and Safety precautions

Causes of accidents: •

Tripping or slipping.



Rock collapse.



Machinery and vehicles related (cranes, excavators, dump trucks etc.).



Flooding or inrush of water.



Electrical installations.



Fire explosion (gas and explosives).



Air pollution (oxygen deficiency, toxic fumes, radon gas).



Air blast or ground shock.



Falling material during hauling.

Safety precautions: Responsibilities of workers: All workers should get trained in use of safety devices and appliances provided to them. All persons entering trench where hazards from falling stones, timber or other materials exist should wear IS approved and certified safety helmets and they should also wear appropriate IS approved and certified safety footwear.

Responsibilities of personnel: All operations inside the tunnel or shaft shall be carried out under the immediate charge of a competent engineer-in-charge. Workmen shall be thoroughly instructed in safety rules. If the geological data collected and information from other sources indicate presence or likelihood of

gases like methane, personnel shall take additional safety precautions necessary on the advice of experts. An accurate record of all accidents shall be properly maintained. Probable reasons of accidents shall be investigated and precautionary measures taken to avoid further recurrence.

Medical and other facilities: •

First-Aid Arrangements: Arrangements for rendering prompt and adequate first-aid to the injured persons shall be maintained at every work site under the guidance of a medical officer-in-charge of the project.



Depending upon the magnitude of the work the availability of an ambulance at a very short notice (at telephone call) shall be ensured.



At least one experienced first-aid attendant with his distinguishing badge shall be available on each shift to take care of injured persons. Arrangements shall be made available for calling the medical officer, when such a need may arise.



Stretchers and other equipment necessary to remove injured persons shall be provided at every shift and portal.



Where there are more than 50 persons working in a shift, effective artificial respiration arrangements shall be provided, with trained men capable of providing artificial respiration.

Miscellaneous: •

Only the materials required for work in progress shall be kept inside the tunnel.



Suitable warning and “NO SMOKING” signs shall be posted in areas where flammable liquids are stored.



Fire extinguishers and fire-buckets appropriate to the hazard should be conveniently located and identified.



Telephone system – A telephone system shall be provided to ensure a positive and quick method of communication between all control locations inside tunnel and portal of the tunnels when longer than 500 m and for shafts when longer than 50 metres.



Warning signals – Irrespective of length and bends in the tunnel, arrangements shall be made for transmitting of warning signals

Public safety:

Shaft sinking and tunneling fascinate the public. Authorized visitors shall be equipped with safety hats and shall be accompanied by a guide competent to keep the visitors out of dangerous situations.

4.

Problems encountered during construction and maintenance of tunnels

4.1.

Loose rocks In this Pranahita - Chevella lift irrigation scheme, package 8, tunnel passes through

competent rock of granite and pink granite which does not need any tunnel supports. Based on the geological investigations rock class below 3 is not encountered throughout the tunnel. But there is always a chance that these geological survey results do not agree with the actual conditions underground.

Control methods: Rock supports in the form of rock bolts, steel ribs and shotcrete are provided where ever necessary and rock bolts are provided at intersections and for stratified rock layers.

4.2.

Seepage water Seepage and rain water is always a problem in tunnel construction. This problem is

excessive in case of underground construction where water table lies above the point of construction. Apart from the seepage water rain water should also be prevented from entering the tunnel.

Seepage water inside tunnel

Seepage control and pumping: A study of boring data and geological formations shall be made have an indication of locations, where water can be expected. This water inflow may be reduced or even entirely stopped by grouting off the wet seams. In case of a steady flow of water from the roof or side of the tunnel the flow shall be deflected down the sides to sumps by metal shields. To prevent seepage water from entering the tunnel rock can be subjected to freezing or water can be pumped out through pumps. The number of pumps provided at site shall be 50 percent more than the requirements calculated on the basis of the estimated pumping needs or at least one, whichever is more. As the tunnel now being constructed is below the water table, excessive seepage problem is encountered. All the water is collected near the pump house from there water is pumped out through a vertical shaft drilled at the end of pump house. After the tunnel is completely driven it is lined with thick concrete layer. Preliminary reason for lining is to arrest seepage.

4.3.

Vibrations

During the blasting of the tunnel rock the surrounding area suffers a little vibration. As the excavation is way below the ground level these vibrations would not be fatal.

Control methods:

In this case it is recommended that the depth of the blast holes shall be limited to 3 to 3.5 metres. This depth is still limited if the residential area is nearer to site location.

5.

Factors to be considered for efficient tunnel construction



Quality Control

Besides maintaining ground stability around the tunnel and ensuring structural integrity of the tunnel lining, proper alignment of the excavation path must be achieved. Two valuable tools are global positioning system (GPS) sensors that receive precise locational data via satellite signals and guidance systems that project and detect a laser beam within the tunnel. ➢

By-products/Waste

Sometimes the earth removed from a tunnel is simply discarded into a landfill. In other cases, however, it becomes raw material for other projects. For example, it may be used to form the base course for an approach roadway or to create roadway embankments for wider shoulders or erosion control. ➢

Speed of erection of supports

Total cost of the project increases with the time taken for construction. To speed up the erection of supports it is essential to: •

Design the support system with minimum number of individual members.



Design the joints with minimum number of bolts.



Fabricate the members with sample bolt and wrench clearances.



Selection of equipment

In order to increase job-site productivity, it is beneficial to select equipment with proper characteristics and a size most suitable for the work conditions at a construction site. Factors that could affect the selection of excavators include: o

Size and time of the job

o

Availability of equipment

o

Cost of transportation of equipment

o

Type of excavation

o

Characteristics of haul units and soil

o

Location of dumping areas

o

Weather

The choice of the type and size of haulers is based on the consideration that the number of haulers selected must be capable of disposing of the excavated materials expeditiously. Factors which affect this selection include: o

Output of excavators: The size and characteristics of the excavators selected will

determine the output volume excavated per day. The size and weight of the haulers must be feasible at the job site and over the route from the construction site to the dumping area. o

Distance to dump site: Sometimes part of the excavated materials may be piled up in

a corner at the job-site for use as backfill. In this package we are dumping the material nearer to the project site. Mud road is provided till the dumping site. o

Probable average speed: The average speed of the haulers to and from the dumping

site will determine the cycle time for each hauling trip. Dump trucks are usually used as haulers for excavated materials as they can move freely with relatively high speeds on city streets as well as on highways. In this package we use dump trucks with a capacity of 25 tons. We load them up to 80 to 90% of their full capacity.

PART III

The Future Exploration methods, materials, and machinery are possible areas of improvement. Sound waves transmitted through the earth can now generate a virtual CAT scan of the tunnel path, reducing the need to drill core samples and pilot tunnels. Some examples of materials research involve cutting tools that are more effective and durable, concrete with more precisely controlled hardening rates, and better processes for modifying soil to make it easier to cut, dig, or remove. Better remote-control capabilities for digging machinery would improve safety by reducing the amount of time people have to be underground during the digging process.

CONCLUSION: Tunnels are viewed as a “green” alternative in many instances, providing for transportation infrastructure or water conveyance without requiring large disturbances to forested areas or animal habitats. Tunnelling is best method for conveying water to elevated areas. In Pranahita – Chevella lift irrigation scheme series of tunnels, pump houses, gravity canals are used to convey water to elevated lands. Drawbacks of tunnel construction are narrow chances for renovation. It is rather complicated construction compared to other water conveyance methods like pipes and canals. Groundwater and loose rocks pose problems during construction. Lot of amount should be spent on the geological investigations and surveying process while this is very less for surface constructions. Though driving a tunnel is a costly process, it has zero maintenance cost. Once tunnel is constructed it needn’t be supervised constantly, unlike other methods of water conveyance. It is well suited where land acquisition is a problem. Tunnels can shorten the distance, whereas canals have to go around a hill or mountain in its way. There will be no losses due to evaporation. Lining arrests seepage losses and reduces hydraulic losses to a great extent. Tunnels are generally constructed for a life period of 100years without any maintenance and operation costs.

REFERENCES: IS 4880: Code of practice for design of tunnels conveying water Part-1 (1987) – General design Part-2 (1976) – Geometric design Part-3 (1976) – Hydraulic design Part-4 (1971) – Structural design of concrete lining in rock Part-5 (1972) – Structural Design of Concrete Lining in Soft Strata and Soils Part-6 (1971) – Tunnel support Part-7 (1975) – Structural design of steel lining

IS 5878: Code of Practice for Construction of tunnels conveying water Part-1 (1971)

– General design

Part-2: Sec-I (1970)

– Geometric design

Part-2: Sec-II(1971)

– Hydraulic design

Part-2: Sec-III (1971)

– Tunnelling Method for Steeply Inclined Tunnels, Shafts and underground power houses

Part-2 (1972)

– Structural Design of Concrete Lining in Soft Strata and Soils

Part-4 (1971)

– Tunnel support

IS 9012: 1978

–Recommended practice for shotcreting

IS 15026: 2002

–Tunnelling Methods in Rock Masses – Guildelines

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