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Piling In Difficult Ground Conditions

Dr.K.S.Rama KrishnaLarsen & Toubro Ltd

ECC-DivisionChennai

Difficult Ground Conditions for Piling

1.Piling in Soft Soils Over Rock

2.Piling in Bouldary Soils

3.Piling with Socketing in Rock

4.Piling on Slopes

5.Piling in Soils with Under water Streams

7.Piling Over Water

Piling with Socketing in Rock

6.Piling Through Loose Fills under High Water Table

27-11-2010L&T-ECC Division : Dr.K.S.Rama Krishna : Piling in Difficult Ground, IGS, Madurai

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Piling With Socketing in Rock

1.Bored Cast-In-Situ Piles with Socketing in Rock

2.Precast Concrete/Steel Piles with Socketing in Rock

Bored Cast-In-Situ Piles with Socketing in Rock


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Bored Cast-In-Situ Piles with Socketing in Rock

Contents: A. Our Current Projects

B. Some Design Aspects

C. Construction Practices

D. Importance of Equipment & Tools

E. A Process Approach Being Followed In L&T Sites

F . Use of Polymer as Drilling Mud

G. Suggested Process for a Sound Rock Socket


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A. Current Infrastructure Projects of L&T with

Bored Piles Socketed in Rock


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Bored Piles Socketed in Rock

-:L&T Projects:-

Project Type of Rock

1. MIAL, Mumbai - Basalt, Breccia, Trachyte

2. Mono Rail, Mumbai - Basalt, Breccia, Trachyte

3. Nasik Elevated Corridor - Breccia, Basalt

4. Bangalore Metro Rail Project - Granite, Gneiss, Schist

5. Chennai Metro Rail Project - Charnockite

6. Hyderabad Metro Rail Project - Laterites, Basalts


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Pile Sizes and Capacities

Project Pile Diameter

(mm)

No of

piles

Compression

Capacity(MT)

MIAL(Mumbai International

Air port)

600,800,1000 5000 140,250,400,500 T

MONO RAIL, Mumbai 800,1000 3000 350,500 T

Nasik Elevated corridor 1000 500 500 T

Bangalore Metro Rail Project 1200 900 500T

Chennai Metro Rail Project 1200 500 500T

Hyderabad Metro Rail Project Design Stage – Monopile Under Consideration


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B. Some Design Aspects for Rock Socketed Bored Piles


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• Rock Socket Friction is a function of

• Surface Roughness of Rock Socket

• Unconfined Compressive Strength of

– Intact Rock

• Confining Stiffness Around the Socket

– in Relation to Fractures of Rock Mass &

– Socket Diameter

• Socket Length-to-Diameter Ratio

Cole & Stroud MethodIS 2911, Part-1, Section 2

• In Hard Rock – 300mm Penetration for Large Diameter Piles

• In Weathred or Soft Rocks:

1) Shear Strength of Rock based on Rock Type

& Quality ( Easy methods of Identification in

Field)

2) Standard Pile Capacity Estimate using inputs

from Point 1 and arrive capacity/Socket

Length27-11-2010

L&T-ECC Division : Dr.K.S.Rama Krishna : Piling in Difficult Ground, IGS, Madurai

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Cole & Stroud

Chart for Piles

socketted in Weak rocks – Basis for Draft IS-

2911 Part I Sec 2


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Cole & Stroud Table for Piles socketed in Weak rocks(Ref: Draft IS-2911 Part I Sec 2)


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IRC SPECIFICATIONS

Qu = Ksp x qc x df x Ab + As x Cus

qc = average UCS of rock

Ksp = An empherical coefficient whose value

ranges from 0.3 to 1.2 for the rocks where

core recovery is reported.

Cus = Ultimate shear strength along socket length =

0.225√(qc), The same shall be restricted to 5Mpa

CR : Core Recovery ; RQD : Rock Quality Designation


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Method -1: Where Rock Cores can be taken & UCS Established

(CR+RQD)/2 Ksp

30% 0.3

100% 1.2

27-11-2010

Pile capacity chart Based on IRC78:2000-Cole and Stroud

Strength/

Consistency (qc)

Strong Moderately

Strong

Moderately

Weak

Weak Very

Weak

Approx N Value > 600 600-400 400-200 200-

100

100-60

Compressive

Strength in Mpa

80-40 40-10 10-4 4-1.4 1.4-0.8

Qu = Re+Raf = Cu.b x Nc x Ab + Cus x As

Where,

Cub = Average shear Strength below base of pile for the depth twice the

diameter/ least lateral dimension of pile.

Cus = Ultimate shear strength along socket length = 0.225√(qc), The same

shall be restricted to 5Mpa

L = Length of socket

Nc = 9

Factor of safety : Skin friction = 10 and End bearing = 5


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Method – 2: When RQD shows Highly Fragmented Strata

IRC SPECIFICATIONS

• Large Diameter Bored piles : Pile Dia > 600mm

• Design :

Safe load capacity = Socket friction+ End Bearing

Minimum socket length: Hard rock = 300mm

Weathered Rock = 0.5x Dia of pile

Ignore top 300mm socket length for calculation of socket friction capacity.

• Friction Capacity Shall be limited to 6 times Diameter of piles

• The allowable end bearing component after dividing by factor of safety

shall be restricted to 5Mpa.

• Minimum Grade of concrete : M35

• Factor of safety on Friction component : 10

• Factor of safety on End Bearing Component : 5

• Minimum Diameter of Pile:

Bridges on land :1000mm

River Bridges : 1200mm


1527-11-2010

• Large Diameter Bored Piles(LDBP) : Pile Dia>600mm

• Design: Granitic & Volcanic Bed Rocks

Safe Load Capacity = Socket Friction + End Bearing

Socket Length ≤ Min (2 x Pile Dia Or 6m)

Ignore top 600mm socket length

• For LDBP : Minimum Grade of Rock = Gr. III

• Allowable Socket Friction:

– Min Gr.II + TCR ≥ 95% + UCS ≥ 50MPa = 700 kPa

– Min Gr.III+ TCR ≥ 85% + UCS ≥ 25MPa = 500 kPa

– Concrete Min 30MPa

– In Case Gr. II & Gr. III met in Pile Bore – USE Gr.III for Socket Friction

• Soil Investigation : – At Every Pile Point:BH = 1 For Pile Dia < 2.5m & 2 for Pile Dia >2.5m

– Continuous Rock Core(N-Size) for Length = 600mm+1.5 Pile Dia below Bed Rock Level

Hong Kong Specifications


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Hongkong- Stringent Quality Standard for Piling

100% predrilling prior to pile drilling

100% verticality check, 10% verticality check by Koden

or as per Specifications

100% Sonic Logging

100% Interface

Full core of pile 5% to 10% depending on

Specifications

Material testing such as cube crushing and Rebar

Tensile Test as per Specifications


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From Tomlinson


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C. Construction Practices


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Design & Construction Compatibility

1. Design of Bored Piles in general & Rock

Sockets in Particular MUST Consider

Construction Practices


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2. Equipment, Tools & Methods Play an Important

Role in Quality, Time and Cost

3. Construction Process(QA/QC) Determines the Capacity

Tripod, Bailer & Chisel Method

3.5 T CHISEL

BAILER

Conventional Tripod System

Productivity :

No.of days per pile,

Depends on Many factors


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Limitations of Tripod- Chisel- Bailer Method

1. Very Slow and some times indefinite

2. Capacity of Chisel is limited by the Winch Capacity

3. It is highly Operator Oriented

4. Very High Quality Supervision Required

5. The Actual Rock in which Pile is socketed is assessed by

indirect method- by energy input

6. Energy is Spent breaking the Entire Rock Mass within the

Socket Portion – Inefficient Method


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Rock Socket Using Rotary Piling Rigs


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BORE PILE CONSTRUCTION SEQUENCE

Bentonite (drilling fluid) fillingCommence drilling

Drilling soil & rock


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BORE PILE CONSTRUCTION SEQUENCE

Solid Rock Core Extracted

Working Sequence for Rock Socket

Construction –Kelly Drilling Method with

Bentonite Mud


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Koden Test For Verticality


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Cores for Concrete Quality


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Pile Toe-Rock Contact Verification by Contact Coring

Tsing Yi Viaduct

Interface Cores recovered


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D. Importance of Equipment & Tools


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Equipment

The Pile Drilling Rig must have sufficient

– Torque

– Crowd Pressure

– Engine Capable of Running without getting heated


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Supported by • Right Type and Quality Tools• Right Method• Experienced Operator


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Bauer-BG-25

27-11-2010

MAIT-HR180


3427-11-2010

Nasik Elevated Corridor Project


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Core Coming

out of the core

barrel

Retrieved

Cores of length

0.5m to 1.4 m

Casagrande

B180

27-11-2010


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Solid rock core recovered on Route 8 Stonecutter

Approach Viaducts

Roller Bit Core Barrel used on Tsing Yi

Viaduct

Solid Rock Cores recovered on Tsing Yi

Viaduct


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THANK YOU


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