BRIDGE FOUNDATION DESIGNSiva

TheivendrampillaiSivakumar

Principal Engineer (Geotechnical)

Geotechnical Branch

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OverviewBrief 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

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Basic Foundation Types

• Shallow FoundationsBearing strata at shallow depths

• Deep Foundation (Piles)Deeper bearing strata

Driven PilesCast-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

WeakCompressibleErodableExpansive

• To resist flood, earth pressuresLateral loadsUplift loadsOverturning loads

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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 pilesDisplacement piles

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

• Cast-in-place piles or Bored pilesNon-Displacement pilesSoil is removedThe excavation may or may not be supported

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Driven Piles - Types and basic requirement in design

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

• Limitations on maximum length

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DRIVEN PILES

PSC Piles in use at Wetheron Creek Bridgesite

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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. VibrationsVibrations

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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:

Lateral movement / Negative skin frictionExcess vertical settlement

• Drive after construction of approach embankments

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Example of NegativeSkin friction

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Bored or Cast-in-place Piles

• TypesShort bored piersCylinders on rockCylinders socketed into rock**

Belled sockets

• Bored pilesCould be up to 4 x cost of driven pile

Bedrock

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Bored Piles - Construction

• Bored piles are cast in place cylindrical piles

• Excavated byAugers

Buckets

Large drill bit (for hard rock)

Chisel grab and casing oscillator for boulderyground, etc.

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Bored Pile Excavation- Augering

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Bored Pile Excavation - Bucket

Cleaning Bucket

Excavation Bucket

Drilling Rig

Rock Sockets

Bored Piles – Cylinders Socketed into rock

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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

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

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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

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Loads on Bridge Foundations

Structural Engineer to advise, consists of but not limited to

• Vertical Compressive (Dead + imposed) loads

Imposed Loads+ ½ Dead Load – highway bridges+ 2/3 Dead Load – railway bridges

• Vertical Upliftflood loads in transverse direction

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Loads on Bridge Foundations

• Horizontal Loadsbraking force of vehicle in longitudinal direction

flood loads in transverse direction

Earthquake

• Horizontal Loads create Bending Moments

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Selection of Foundation Type

What influences the decision for driven or bored piles?The following factors will influence the choice of foundation type:

LoadsEnvironmentLogistics andGeology

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Selection of Foundation Type: Loads

• Structural LoadsHeavy compressive loads from large spans

• Hydraulic IssuesLateral and uplift loads from flood loading

Scour in loose sands and silts

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Selection of Foundation Type: Environment

• Vibration proximity to people vulnerable structuresdamage to services

• Aggressiveness due to groundwater • Obstructions

overhead power lines / headroom

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Selection of Foundation Type: Logistics

• Transporting fresh concrete in western Queensland

Distance and temperature

• Availability/Transporting PSC pilesMax length around 25 – 27m

• Quality of access roads

• Accessibility at foundation locationsCrane pads, piling rig pads

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Selection of Foundation Type: Geology

• Depth to competent strata• Obstructions to pile driving

Coffee rock (Indurated Sand)

• Steeply dipping bearing strataBasalt flows

• Interbedded rock types with different properties

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Selection of Foundation Type: Geology

• Compressible deposits• Defects with soft infills• High head of groundwater

Sealing issuesHole stabilityConcreting

• Rock excavatability

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Coffee Rock (Indurated Sand)

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Steeply Dipping Bearing Strata

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PILE DESIGN

THEORY EMPIRICISM EXPERIENCE FIELD LOADING TESTS

Engineering GeologySoil Mechanics

Rock MechanicsStructural Mechanics

To account for various methods of

pile installation

Regional (geology + local construction

practices)

StaticDynamic

Design Stage

Construction Stage

Pile Design - Approaches

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PILES PILES -- designdesign

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

• Foundations:Load capacitySettlementsLateral FixityUplift resistance

• Scour IssuesLand/water structures

• ApproachesStabilitySettlements

• InteractionAbutmentsWidening/ duplication

The following DESIGN ELEMENTS should be accountedfor in design:

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Pile Capacity

• Q = Pile Capacity

• Qend = End Resistance

• Qshaft = Shaft Resistance

• Q = Qend + Qshaft

Q

Qshaft

Qend

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End versus Shaft Bearing Piles• Pile in Clay • Pile in

SandEnd Bearing Pile

Qshaft

Qend = 5-10% Qshaft

Qshaft

Qend

Qshaft

Qend

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Low load Ultimate load

fs = τ max

fs = τ max

for the full

lengthfs << τ max

Base resistance, fb, mobilized

Driven Pile Capacity

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Design of PilesTraditional ApproachUltimate 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.

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Design of PilesLimit 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)

Load and Settlement- (idealized)

(600 mm, 10 m long bored pile in stiff clay)

PILE DESIGN – WIDELY ACCEPTED BEHAVIOUR

Pile

NONDISPLACEMENTDrilled shafts

Micropiles in soils

CFA(Auger cast)

PARTIAL DISPLACEMENTH-Piles

Open-ended pipe piles(in some soils)

FULL DISPLACEMENTPrecast concrete

Closed-ended pipe pilesOpen-ended pipe piles

(in some soils)Franki

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

bearing capacity.

Increasing unit base or shaft resistance

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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 TestDerivation of design parameter

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 testStatic Load Test (Kentledge or Reaction Piles)

Dynamic Test (PDA with CAPWAP)

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Static Load Test

Reaction Piles

Kentledge

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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 ofTwo strain transducers (to measure strain/force)

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.

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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

Load-settlement Behaviour

Test Pile: Predicted versus Measured Performance

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

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

Old River ChannelsPaleo-channels (very dangerous)

Paleo-channels

• GUP, near Schultz canal

• From old topography maps and airphotos

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• Paleochannels

Old buried channels from previous creek routes

Deposits of softer younger alluvium

Can be difficult to identify

Create a sudden change in ground conditions

Abutment Stability and Settlement

Paleo-channels – Long Section

10 – 15m soft clay

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Abutment Stability and Settlement

• Risks associated with soft claysEmbankment stability and settlementStructures (damage, bumps)Pavements Deterioration - unevennessRetaining wall foundationsConstruction delays Construction access

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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

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Abutment Stability and Settlement: Soft Clay Issue, Differential Settlement

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Abutment Stability and Settlement: Typical Exampleson Projects in South East Queensland

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

Dinmore

Gateway Arterial – Bald Hills Creek, Stability

Gateway Arterial - Bald Hills Creek

• 3m high embankment

• 100m failure during construction

• Boreholes 150m apart

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Bald Hills Creek - Mitigation Strategy

• Stability failure reinstated with timber piled raft• Abrupt differential settlement between

embankment sectionsEmbankment on piles didn’t settleEmbankment on natural did (4-5mm /month)

Bald Hills Creek, Settlement

≈ 800 mm by Jul 98

≈ 150 mm predicted in 1986 by consultant

East – West Arterial @ Pound Drain

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East – West Arterial @ Pound Drain

• Damaged by lateral loading on piles from the approach embankment

• Differential settlement alsoLoads on abutment piled foundations

Interaction effects on adjacent structures

Functionality of drainage structures

Problems at relieving slab and pavement

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Ipswich Motorway Ipswich Motorway -- Bridge Bridge BR340, StabilityBR340, Stability

•• Number of Spans = 3Number of Spans = 3

•• Span Length = 13m, 18m & 13mSpan Length = 13m, 18m & 13m

•• Bridge Bridge SpillthroughSpillthrough Embankment Embankment

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

•• Number of Piles at Abutments = 3Number of Piles at Abutments = 3

Spaced at 6.5m Spaced at 6.5m c/cc/c

•• Number of Piles at Piers = 5Number of Piles at Piers = 5

Spaced at 3.3m Spaced at 3.3m c/cc/c

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Ipswich Motorway - 2009

Approach Approach embankment failed. embankment failed. Cracks in embankmentCracks in embankmentplus Pier piles displaced.plus Pier piles displaced.

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Risks Associated with Soft Clays – ManagingStability 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

Total Replacement

Temporary Surcharge

Height reduction.Counter Berms

Stage Construction

Vertical Drains

Reinforced Embankment

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SELECTION OF DESIGN PARAMETERS

• SOILS• ROCKS

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Soils

SAND

CPT SPT

CLAY

OedometerConsolidation

Stiff Soft

UU CPT CPTu UU

SPT: Standard PenetrometerCPT: Cone PenetrometerCPTu: PiezoconeUU: TriaxialVS: Vane Shear Test

VS

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Selection of Design Parameters : CPT

CPT

Sands / Stiff Clays

fs qc

Shaftresistance

End bearing resistance

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Selection of Design Parameters : CPTu

CPTu

Soft Clays

qc u

Su (Undrained Strength for stability)

Cv (Rate of settlement)

Drainage lenses

Fs/qc/u

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Selection of Design Parameters : Su

Undrained Strength

Soft clayStiff Clay

StabilityShaft Resistance

End Bearing

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Selection of Design Parameters: Rock

XW/HW

Visual SPT Point Load

MW/SW

Visual USC Point Load

Pressure -meter

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Selection of Design Parameters: Rock Tests

UCS PressuremeterPoint Load (Is)50

HW/MW/SW/Fr

Settlement of Sockets

Shaft Resistance

End Bearing

CNS

MW/SW/Fr

Shaft Resistance

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Design Charts (after Poulos)

• Design charts for the estimation of shaft resistance and settlement of pilesDriven PilesBored Piles

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Shaft Resistance

Settlement (Poulos 1989)

Settlement (Poulos 1989)