Bridge Course Ts 2010 Fbook

BRIDGE FOUNDATION DESIGN Siva Theivendrampillai Sivakumar Principal Engineer (Geotechnical)

Geotechnical Branch

Overview Brief Discussion on: • Foundation Type • Foundation Design • Pile Load Testing • Approach Embankment to Bridge

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TMR-Specifications • • • •

Cast-in-Place Piles – MRTS63 and 63A Driven PSC Piles – MRTS65 Driven Steel Piles –MRTS66 Dynamic Testing of piles—MRTS68

• Project Specific- Geotechnical Design Standard – Minimum Requirements 3

Basic Foundation Types • Shallow Foundations ¾ Bearing

strata at shallow depths

• Deep Foundation (Piles) ¾ Deeper

bearing strata

ƒ Driven Piles ƒ Cast-in-Place Piles

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Basic Foundation Types

SHALLOW FOUNDATIONS

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When can we use Shallow Foundations? When Surface strata are: • Strong ( Adequate bearing capacity and no settlement issues). • Not vulnerable to Scour • Non-expansive • Low ground water level

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Shallow Foundation Design – Things to Consider

• Concentric / Eccentric Loading • Overturning moment • Sliding • Global Stability ( esp. footing on / adjacent to slope)

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Basic Foundation Types

DEEP FOUNDATIONS - PILES

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When do we need piles? • When surface strata are ¾ ¾ ¾ ¾

Weak Compressible Erodable Expansive

• To resist flood, earth pressures ¾ ¾ ¾

Lateral loads Uplift loads Overturning loads 10

Pile Use: Transfer load through surface strata which may be weak, compressible, expansive etc.

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Pile Use: For resisting lateral loading

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Pile Use: For resisting uplift

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Pile Use: Support against scour or lateral loading due to excavation

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Pile Use – Further example of lateral support for deep excavation induced lateral loading

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Deep Foundations - Pile Types • Driven piles ¾ ¾

Displacement piles Soil is ‘displaced’ within the adjoining soil mass (displaced volume ≈ pile volume)

• Cast-in-place piles or Bored piles ¾

Non-Displacement piles

¾

Soil is removed

¾

The excavation may or may not be supported 16

Driven Piles - Types and basic requirement in design • Types ¾

¾ ¾ ¾

Octagonal Prestressed Concrete (PSC) Reinforced Concrete (RC) Steel “H Pile” Timber Piles

• Limitations on maximum length 17

DRIVEN PILES

PSC Piles in use at Wetheron Creek Bridgesite 18

Pile Driving Frame

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SITE INVESTIGATION FOR DRIVEN PILES

1. Soil strength and stiffness 2. Soil chemical analysis ⇒ corrosion/aggressiveness 3. Possible obstructions to installation 4. Potential for damage to adjoining structure due to “ground heave” 5. Vibrations

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Driven Piles • Will refuse in SPT N>50 material • Loads: e.g.,550mm PSC working 1500kN • Settlement: ~ 10 mm • Vulnerable to: ¾

Lateral movement / Negative skin friction

¾

Excess vertical settlement

• Drive after construction of approach embankments 21

Example of Negative Skin friction

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Bored or Cast-in-place Piles • Types ¾ ¾ ¾ ¾

Short bored piers Cylinders on rock Cylinders socketed into rock** Belled sockets Bedrock

• Bored piles ¾

Could be up to 4 x cost of driven pile 23

Bored Piles - Construction • Bored piles are cast in place cylindrical piles • Excavated by ƒ

Augers

ƒ

Buckets

ƒ

Large drill bit (for hard rock)

ƒ

Chisel grab and casing oscillator for bouldery ground, etc.

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Bored Pile Excavation- Augering

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Bored Pile Excavation - Bucket Cleaning Bucket

Drilling Rig Excavation Bucket

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Bored Piles – Cylinders Socketed into rock

Rock Sockets

Rock Sockets • • • • •

High compression loads Greater resistance to lateral movement Socket length 2 to 5 x diameter Diameter from 900mm to 1800mm High strength rock ¾ Point

Load (Is50 > 1 MPa) ¾ Rock anchors preferred to resist large uplift loads 28

Rock Sockets • May need casing in overburden soils and XW rock (SPT N<50) • Sealing/control of groundwater important • Capacity to take heavy loads dependent on extremely clean socket bases – inspection important (WH&S) • More expensive - so fewer, larger piles may be more economical 29

Loads on Bridge Foundations Structural Engineer to advise, consists of but not limited to •

Vertical Compressive (Dead + imposed) loads

¾ Imposed Loads ¾ + ½ Dead Load – highway bridges ¾ + 2/3 Dead Load – railway bridges • Vertical Uplift ¾

flood loads in transverse direction 30

Loads on Bridge Foundations • Horizontal Loads ¾

braking force of vehicle in longitudinal direction

¾

flood loads in transverse direction

¾

Earthquake

• Horizontal Loads create Bending Moments 31

Selection of Foundation Type What influences the decision for driven or bored piles? The following factors will influence the choice of foundation type: 9 Loads 9 Environment 9 Logistics

and

9 Geology

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Selection of Foundation Type: Loads • Structural Loads ¾

Heavy compressive loads from large spans

• Hydraulic Issues ¾

Lateral and uplift loads from flood loading

¾

Scour in loose sands and silts

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Selection of Foundation Type: Environment

• Vibration ¾ ¾ ¾

proximity to people vulnerable structures damage to services

• Aggressiveness due to groundwater • Obstructions ¾

overhead power lines / headroom

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Selection of Foundation Type: Logistics • Transporting fresh concrete in western Queensland ¾

Distance and temperature

• Availability/Transporting PSC piles ¾

Max length around 25 – 27m

• Quality of access roads • Accessibility at foundation locations ¾

Crane pads, piling rig pads 35

Selection of Foundation Type: Geology • Depth to competent strata • Obstructions to pile driving ¾

Coffee rock (Indurated Sand)

• Steeply dipping bearing strata ¾

Basalt flows

• Interbedded rock types with different properties 36

Selection of Foundation Type: Geology • Compressible deposits • Defects with soft infills • High head of groundwater ¾

Sealing issues

¾

Hole stability

¾

Concreting

• Rock excavatability 37

Coffee Rock (Indurated Sand)

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Steeply Dipping Bearing Strata

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Pile Design - Approaches PILE DESIGN THEORY

Engineering Geology Soil Mechanics Rock Mechanics Structural Mechanics

EMPIRICISM

To account for various methods of pile installation

EXPERIENCE

Regional (geology + local construction practices)

FIELD LOADING TESTS Static Dynamic

Design Stage

Construction Stage

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PILES - design The following aspects should be considered in design: 1. Load carrying capacity (Geotechnical Engineer) - strength and stiffness ⇒ “serviceability” 2. Pile material strength (Structural Engineer) 3. Pile material durability (Structural Engineer)

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Pile Design - Geotechnical The following DESIGN ELEMENTS should be accounted for in design:

• Foundations: ¾ ¾ ¾ ¾

Load capacity Settlements Lateral Fixity Uplift resistance

• Scour Issues ¾

Land/water structures

• Approaches ¾ ¾

Stability Settlements

• Interaction ¾ ¾

Abutments Widening/ duplication 42

Pile Capacity • Q

= Pile Capacity

Q

• Qend = End Resistance • Qshaft = Shaft Resistance • Q

Qshaft

= Qend + Qshaft Qend 43

End versus Shaft Bearing Piles • Pile in Clay

• Pile in Sand

Qshaft

Qend = 5-10% Qshaft

ƒ End Bearing Pile

Qshaft

Qend

Qshaft

Qend 44

Ultimate load

Low load

fs = τ max fs = τ max

fs << τ max

Base resistance, fb, mobilized

for the full length

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Driven Pile Capacity

Design of Piles Traditional Approach Ultimate Geotechnical Capacity = Ult. Skin Friction + Ult. End Resistance Allowable Geotechnical Capacity = Ult. Skin Friction/1.5 + Ult. End Resistance/3.0 OR

Allowable Geotechnical Capacity = Ultimate Geotechnical Capacity/2.5 The allowable geotechnical capacity should be compared with design load (unfactored) from the structure. 47

Design of Piles Limit State Design (e.g AS2159) Rug (Ultimate Geotechnical Capacity) = Ult. Skin Friction + Ult. End Resistance Rg* (Design Geotechnical Capacity) = Ф x Rug Rg* >= N* or S*

(Design Action Effect or Ultimate Design Load)

Rg* should be compared with ultimate design load (not driving capacity or structural capacity) 48

Load and Settlement- (idealized) (600 mm, 10 m long bored pile in stiff clay)

PILE DESIGN – WIDELY ACCEPTED BEHAVIOUR Increasing unit base or shaft resistance Pile NONDISPLACEMENT Drilled shafts Micropiles in soils

CFA (Auger cast)

PARTIAL DISPLACEMENT H-Piles Open-ended pipe piles (in some soils)

FULL DISPLACEMENT Precast concrete Closed-ended pipe piles Open-ended pipe piles (in some soils) Franki

Spectrum of soil displacement caused by pile installation and Its relationship to bearing capacity.

2nd Session • Pile Load Testing • Site Investigation – Need to get it right • Design Elements – Stability and Settlement at Bridge Approaches • Selection of Design Parameters • Design Charts – for estimating shaft resistance and settlement of piles

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Pile Load Test • Why Pile Load Test ¾

Derivation of design parameter

¾

Verification of design load or pile carrying capacity

• MRTS63 Requires that at least 10% of piles at a site to be tested • Common methods of pile load test ¾

Static Load Test (Kentledge or Reaction Piles)

¾

Dynamic Test (PDA with CAPWAP) 52

Static Load Test Kentledge

Reaction Piles

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Kentledge Set up for Static Pile Load Test

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Static Load Test – Further example of Kentledge

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Dynamic Load Test – Pile Driving Analyser (PDA) • The PDA system consists of ¾

Two strain transducers (to measure strain/force)

¾

Two accelerometers (to measure velocity)

Attached to opposite sides of the pile (near the top of the pile).

• The measured force and velocity at the pile top provide necessary information to estimate soil resistance and its distribution. 56

PDA – Set Up

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Typical arrangement of PDA - Schematic

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Force & velocity wave traces recorded during initial driving and restriking

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Load-settlement Behaviour

Test Pile: Predicted versus Measured Performance

Site Investigation - Need to get it right

• What can go wrong? • How can we manage undue contractual claims as well as save construction time • Limited investigation can be disastrous as this could lead to undue claims • Example – Six Mile Creek, Central Qld

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Six Mile Creek, Central Qld

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Six Mile Creek – Footing Plan Area

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Six Mile Creek: Additional Investigation-DCP

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Six Mile Creek - Footing Excavation

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Six Mile Creek: Footing re-design

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Design Element – Stability and Settlement at Bridge Approaches

• Stability • Settlement

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Different Origins that could Lead to Formation of Bump at the Approaches to a Bridge

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Abutment Stability and Settlement • Compression of Natural Soil Due to Embankment Load • What are compressible Soils? ¾ Soft

clays (SPT N = HW to 6 or Su <25kPa)

• Where can we find soft clays (compressible soils)? ¾ Old

River Channels ¾ Paleo-channels (very dangerous) 70

Paleo-channels • GUP, near Schultz canal • From old topography maps and airphotos

Abutment Stability and Settlement

•

Paleochannels ƒ

Old buried channels from previous creek routes

ƒ

Deposits of softer younger alluvium

ƒ

Can be difficult to identify

ƒ

Create a sudden change in ground conditions 72

Paleo-channels – Long Section

10 – 15m soft clay

Abutment Stability and Settlement • Risks associated with soft clays ¾Embankment stability and settlement ¾Structures (damage, bumps) ¾Pavements Deterioration - unevenness ¾Retaining wall foundations ¾Construction delays ¾Construction access 74

Abutment Stability: Soft Clay Issue Slip Failure - Schematic

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Abutment Stability and Settlement: Soft Clay Issue

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Abutment Stability and Settlement: Soft Clay Issue, Bump at Bridge Approach

Vertical Settlement 77

Abutment Stability and Settlement: Soft Clay Issue, Differential Settlement

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Abutment Stability and Settlement: Typical Examples on Projects in South East Queensland

• Gateway Arterial @ Bald Hills Creek • East – West Arterial @ Pound Drain • Ipswich Motorway – BR340 @ Dinmore

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Gateway Arterial – Bald Hills Creek, Stability

Gateway Arterial - Bald Hills Creek • 3m high embankment • 100m failure during construction • Boreholes 150m apart

Bald Hills Creek - Mitigation Strategy • Stability failure reinstated with timber piled raft • Abrupt differential settlement between embankment sections ƒ

Embankment on piles didn’t settle

ƒ

Embankment on natural did (4-5mm /month)

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Bald Hills Creek, Settlement

≈ 150 mm predicted in 1986 by consultant ≈ 800 mm by Jul 98

East – West Arterial @ Pound Drain

East – West Arterial @ Pound Drain • Damaged by lateral loading on piles from the approach embankment • Differential settlement also ¾Loads on abutment piled foundations ¾Interaction effects on adjacent structures ¾Functionality of drainage structures ¾Problems at relieving slab and pavement 85

Ipswich Motorway - Bridge BR340, Stability •

Number of Spans = 3

•

Span Length = 13m, 18m & 13m

•

Bridge Spillthrough Embankment 9m high with batter Slopes 1(H):1(V)

•

Number of Piles at Abutments = 3 Spaced at 6.5m c/c

•

Number of Piles at Piers = 5 Spaced at 3.3m c/c

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Ipswich Motorway - 2009 Approach embankment failed. Cracks in embankment plus Pier piles displaced.

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Risks Associated with Soft Clays – Managing Stability and Settlement

• How can we manage stability and settlement

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Overview of Management Strategies

Light-weight Fill

Stone Columns

Embankment on Piles

Vacuum Preload

Partial Replacement

Stage Construction

Reinforced Embankment

Total Replacement

Temporary Surcharge Counter Berms

Height reduction.

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Vertical Drains

SELECTION OF DESIGN PARAMETERS • SOILS • ROCKS

90

Soils CLAY

SAND

Soft

Stiff

CPT

SPT

UU

SPT: Standard Penetrometer CPT: Cone Penetrometer CPTu: Piezocone UU: Triaxial VS: Vane Shear Test

CPT

CPTu

UU

VS

Oedometer Consolidation 91

Selection of Design Parameters : CPT

CPT Sands / Stiff Clays

fs Shaft resistance

qc End bearing resistance

92

Selection of Design Parameters : CPTu CPTu

Soft Clays

qc Su (Undrained Strength for stability)

u Cv (Rate of settlement)

Fs/qc/u Drainage lenses 93

Selection of Design Parameters : Su Undrained Strength

Soft clay

Stability

Stiff Clay Shaft Resistance End Bearing 94

Selection of Design Parameters: Rock XW/HW

Visual

SPT

MW/SW

Point Load

Visual

USC

Point Load

Pressure -meter

95

Selection of Design Parameters: Rock Tests Point Load (Is)50

UCS

Pressuremeter

HW/MW/ SW/Fr Shaft Resistance End Bearing

CNS

MW/SW/Fr

Settlement of Sockets

Shaft Resistance 96

Design Charts (after Poulos) • Design charts for the estimation of shaft resistance and settlement of piles ¾Driven Piles ¾Bored Piles

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Shaft Resistance

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Settlement

(Poulos 1989)

Settlement

(Poulos 1989)