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

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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

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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

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Buckets

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Large drill bit (for hard rock)

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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