1. Introduction

2. Construction practices

3. Field Testing and Numerical Simulation

4. Case Studies

Presentation Outlines

Pile foundations have been used as load carrying and load transferringsystems for many years

Early days of civilization from the communication, defence or strategicpoint of view villages and towns were situated near to rivers andlakes.

Strengthen the bearing ground with some form of piling

Timber piles were driven in tothe ground by hand or holeswere dug and filled withsand and stones

In 1740 Christoffoer patheminvented pile drivingequipment which resembledto days pile drivingmechanism.

Steel piles have been used since1800 and concrete pilessince about 1900

• The industrial revolutionbrought about importantchanges to pile driving systemthrough the invention of steamand diesel driven machines

• More recently, the growingneed for housing andconstruction has forcedauthorities and developmentagencies to exploit lands withpoor soil characteristics.

• This has led to thedevelopment and improvedpiles and pile driving systems.Today there are manyadvanced techniques of pileinstallation

And then…

PILE FOUNDATION•Piles are structural membersthat are made of steel,concrete or timber.

•Used to support the structureand transfer the load atdesired depth either by endbearing or skin friction.

•Pile foundations are usuallyused for large structures andin situations. where the soil atshallow depth is not suitableto resist excessive settlement,resist uplift, etc.

What is Residual soils ?

• Soils that form from rock weathering or accumulation of organic material and

remain at the place where they were formed are Residual Soils.

• Residual soil profiles generally show a gradual transition from soil to rock, rather

than a distinct line of separation of soil and rock.

• The degree of disintegration may vary appreciably over the thickness of its stratum.

What is a Large diameter pile ?

• Pile foundations of diameter greater than 1 m are usually termed “Large Diameter”

• Monopiles of 4.0 m and 4.7 m diameter have been used .

• Monopiles of 1.6 m and 1.2 m dia have been used in the construction of the

Bangalore Metro and other major infrastructure projects.

Terminology

• Identifying the transition between the sub-strata layers.

Sometimes IGM can be mistaken for bedrock.

• At what depth should the pile be terminated?

• How large should the diameter of the pile be?

India:1.6m Abroad: Upto 4-4.7 m

• Should one socket in IGM or rock?

• How deep should the socket should be?

• Testing techniques developed, proven for small dia

piles only

• Predicting Load-Displacement relationships

• Know-how on grouting to improve load bearing

capacity.

Issues in Large Diameter Piles Foundations in Residual Soils

*Intermediate geometrical(IGM)

Field exploration &Testing

Geotechnical analysis of Bored cast-in situ

Axial & Lateral ultimate capacity

Load displacement curve

Final GeotechnicalRecommendations

Final Design/Drwg/Specification

constructionFinal QA/QCNon Destructive test

Field testPDA/PIT

Final acceptance

Design and Construction of Pile foundation Process

CURRENT PRACTICES

• IS:2911(Part I/Sec-2)-1979(Reaffirmed 2002) Code of practice forDesign & Construction of pile foundations . Part I: Concrete Piles;Section 2: Bored cast-in-situ concrete piles.

• IS:2911(Part 4)-1980 Code of practice for Design & Constructionof pile foundations. Part 4: Load tests on pile.

• Generally Large Diameter Piles not used in India till recently; lack of availability of large cutters, buckets and drill rigs.

Small Diameter Pile Foundations Large Diameter Pile foundations

Construction Equipment

Silty

Cla

yW

eath

ered

Roc

k

Typical Bore log Report

• Site: Agara Junction, HSR Layout

• Borehole Diameter: 150 mm

• GWT: No

• Type of Boring: Rotary Drilling

13.8

m11

.2 m

1 m Parameters Description

Lege

nd

Dep

th(m

)

Sam

ple

N-V

alue

Greyish Yellow Sand Silt with Clay Binders

0.0 -- --

1.5 DS --

c = 20 KN/m2 4.0 UDS --

Ø = 20º4.5 SPT

DS 7γ =14KN/m3

5.5 UDS --

6.0 SPT DS 13

7.5 SPT DS 18

9.0 SPT DS 26

13.8 SPT DS 40

Yellowish Grey Weathered Rock

with the Prescence of Mica

c = 10 KN/m2

Ø = 35º15.0 SPT

DS 60γ = 20 KN/m3

20.0 SPT DS 80

3.2

m

• There are lot of problems in borehole

method of investigations

• New geophysical methods are available to

identify bed rock and soil profiles – eg.

MASW testing

Single pile under Vertical Axial Load

AIM:

• The purpose of this case study is to simulate the pile-loading test using Numerical simulation, and compare the simulation results with the field pile load test results of Sommer & Hambach (1974) and analytical methods (equations).

* Before I going to my field test results, here excellent field pile load tests results conducted by Sommer & Hambach(1974) by using load cells at the pile base to measure the loads directly at pile base

Field pile load test results of Sommer & Hambach (1974).• The reaction beam was supported by 16 anchors (Fig).

• The loading system consists of 2hydraulic jacks working

against a reaction beam.

• The loads were applied in increments and maintained

constant till the settlement rate was negligible.

• The pile diameter of 1.3m & length of 9.5m

• Load cells were installed at the pile base to measure the

loads carried directly by pile base.

• The upper 4.5m subsoil consist of silt followed over

consolidated clay to great depths.

• The ground water table is about 3.5m below the ground

surface.Fig: Schematic of load test

Layout of 16anchors in load test

Field Vertical pile load test data

Ultimate Load capacity

Method Load(kN)

Single abscissa 2000

12 mm Diameter 2250

Double abscissa 2750

10% Diameter -----

• This test is for a large diameter pile (diameter = 1300 mm), (Length = 9.5m)• Has been carried out properly:

• Linear and non-linear portions clearly visible• Test carried out to failure (12mm)

• Methods to determine Ultimate Load Bearing capacity shown in the table can be used effectively

0

5

10

15

20

25

30

35

0 500 1000 1500 2000 2500 3000 3500

Sett

lem

ent (

mm

)

Load (kN)

Total Load [kN]

Sommer & Hambach (1974-Germany).

Axi Symmetry geometry model.

The element mesh - 15-node element.

Geometry : 2D: 4m x 14.5m

Pile radius:0.65m ; Length: 9.5m .

5 noded beam-column element. 3 DoF per node.

Ground water table is located at 3.5m.

Stage-wise loading done, upto 3250kN.

Numerical Simulations

SOIL PROPERTIES AND PILE DETAILSParameter Symbol Silt OCR Clay Concrete pile Unit

Material Model Mohr-Coulomb Hardening-Soil Linear Elastic [-]

Behaviour Type Drained Drained Non-porous [-]

Dry Weight gunsat 19 20 25 [kN/m³]

Young’s Modulus Eref 10E+3 10E+3 30E+6 [kN/m²]

Poisson’s Ratio n 0.3 0.2 0.2 [-]

Cohesion cref 5 21 - [kN/m²]

Friction Angle j 27.5 21 - [°]

Linear Elastic: Stress & strain are linearly proportional. No failure, tensile stresses allowed. MC: Linear elastic until yield and further perfectly plastic. The model involves five parameters

namely E,ν,φ,c,ψ. Loading and unloading modulus are the same. HS: More versatile. MC strength parameters. Different loading and unloading modulus

Sommer & Hambach (1974).

Very

Fin

e

Fine

Mesh size

• The “Medium” mesh curve is the closest to the field tests data.

• The “Medium” mesh is used in all of the following simulations.

Aro

und

1000

elem

ents

Aro

und

500

elem

ents

0

5

10

15

20

25

30

35

40

0 250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500

Sett

lem

ent (

mm

)

Load (kN)

Total Load [kN]

Fine

Very fine

Medium

Aro

und

250

elem

ents

Medium

Sommer & Hambach (1974).

Evaluating End Bearing & Skin Friction from Numerical simulation

0

5

10

15

20

25

30

35

40

0 250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500

Sett

lem

ent (

mm

)

Load (kN)

Total Load [kN]

Skin Friction [kN]

Base Load [kN]

Total Load with Plaxis

Base Load Plaxis

Skin Friction Plaxis

Method Skin friction (kN)

End bearing (kN)

Total Load( kN)

IS code 3674 1646 5320Meyerhoff’s 1940 8840 10780PLAXIS 2D 2183 1067 3250

Sommer & Hambach (1974).

Where,Qu is the Ultimate Bearing CapacityAp is the Cross Section Area of PileD is the Stem Diameter of Pileγ is the Unit Weight of the SoilNγ and Nq are Bearing Capacity FactorsPD is the Effective Overburden Pressure

Ki is the Coefficient of Earth PressurePD1 is the Effective Overburden of corresponding layerδ is the Angle of Wall FrictionAsi is the Surface Area of the corresponding layerN is the Average SPT in the region of the shaft

Qu = Ap (0.5Dγ Nγ) + Ap (PD Nq) +∑ Ki PD1 tanδ Asi Qu = (40NAp) / 3+ (N As) / 5

Various approaches to determine Ultimate Load Bearing capacity Method 1: IS:2911(Part I/Sec 1) code Method 2: Meyerhoff’s Method

• Based on Shear strength parameters(Lab Testing) • Based on Standard Penetration Test (Field Testing)

Pile Diameter: 1.3 m ; Pile Length: 9.5m

Method Skin friction (kN)

End bearing (kN)

Total Load

( kN)

IS code 3674 1646 5320

Meyhorff’s 1940 8840 10780

ANALYTICAL METHODS

FIELD ULTIMATE LOAD= 2000 TO 2750 KN

*In small diameter piles these methods are quitesuitable , but not in large diameter

• Foundations for urban flyover bridge structures are generally built ondeep foundations using cast-in-situ piles.

• The metro rail project of Bengaluru has employed precast post-tensioned prestressed concrete girders of spans 25 m to 30 m whichare supported on massive cast-in-situ piers supported on large pilecaps combining nine piles of 1 to1.6 meter diameter, each cast at siteover a depth 15m to 30m resting on rocky strata.

Pile Dia 1.2 m

Bangalore Metro Project

4. Flyover (HSR Layout)-Group of piles (4)Dia 1.0 m

2. Metro (M.G Road)-MonopilesDia 1.6 m

1. Metro(Jayanagar)-Group of piles (4)Dia 1.2 m

3.Flyover(Kalyan nagar )-Group of piles (5)Dia 1.2 m

FEW PILE LOAD TESTS WHERE I WAS INVOLVED

Field Tests: Routine Vertical Load Test

•Test load is applied on the pile by jacking against a reaction frame which is either loaded with kentledge• Hydraulic jack to apply load on pile head. For more accurate measurement of load, a load cell or

proving ring may be used• Displacement of the pile head is measured by dial gauges ( 3 or 4 nos.) • Load is applied in suitable increments and settlement observed• Each load should be maintained for 2 hours or till the rate of settlement becomes 0.2 mm/hour, whichever is earlier.

• This test is for a large diameter pile (diameter = 1000 mm)• Has not been carried out properly:

• Non-linear portion incomplete• Test carried out neither to 12mm settlement nor to meet 10%-of diameter regulation.

• The 10% of diameter method to determine Ultimate Bearing Capacity cannot be used.• The double abscissa method would be more accurate if larger loads were used.• 10% of dia is 100mm. Achieving such settlements may be impractical and unnecessary. • Guideless needs to be modified as they were made for smaller dia piles.• Current codes need to be modified or testing till 12mm should be deemed sufficient.

Site : Kalyan Nagar

0

0.5

1

1.5

2

2.5

3

0 2000 4000 6000 8000 10000

Set

tlem

ent

(mm

)Load (kN)

No Ground water table is located.

Stage-wise loading done , upto 8250kN.

Numerical Simulation

Axi Symmetry geometry model.

The element mesh - 15-node element.

Geometry : 2D: 5m x 20m

Pile radius:0.5m ; Length: 15m .

5 noded beam-column element. 3 DoF per node.

Comparison of Field test & Numerical simulationSite 3 :Kalyan nagar

Method Skin friction (kN)

End bearing (kN) Total Load( kN)

IS code 5700 4620 10320

Meyerhof’s 2830 7540 10740

PLAXIS 2D 6608 1642 8250

Ultimate load capacity of pile by different methods

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 3000 6000 9000 12000

Sett

lem

ent (

mm

)

LOAD (kN)

Field curve

PLAXIS 2D CURVE

BASE LOAD BY PLAXIS

ObservationAnalytical method(Iscode) isreasonably matching with skinfriction obtained from Numericalsimulation. It is also noticed that field curvehas shown a different shape startingfrom 2mm settlement, which maybe attributed to field test problems. Out-dated methods used to record data, time consuming, labour intensive, costly. – Quality issues So, we need to suggest some alternative techniques which are more reliable – With proper instrumentation .

0

0.5

1

1.5

2

2.5

3

3.5

4

0 2000 4000 6000 8000 10000 12000 14000

Set

tlem

ent

(mm

)Load (kN)

• This test is for a large diameter pile (diameter = 1200 mm)• Has not been carried out properly:

• linear portion is present – non linear is not present.• Test carried out neither to 12mm settlement nor to meet 10%-of diameter regulation.

• The 10% of diameter method to determine Ultimate Bearing Capacity cannot be used.• The double abscissa method would be more accurate if larger loads were used.• 10% of dia is 120mm. Achieving such settlements may be impractical and unnecessary. • Regulation needs to be studied as they were made for smaller dia piles.• Current codes need to be modified or testing till 12mm should be deemed sufficient.

Site : Jayanagar

Field Pile load test

Comparison of Field test & Numerical simulation

0

0.5

1

1.5

2

2.5

3

3.5

4

0 2000 4000 6000 8000 10000 12000 14000

SETT

LEM

ENT

(mm

)

LOAD kN

FIELD CURVE

TOTAL LOAD WITH PLAXIS CURVE

BASE LOAD BY PLAXIS

SKIN FRICTION BY PLAXIS

Ultimate load capacity of pile by different methodsMethod Skin friction

(kN)End bearing

(kN)Total Load

( kN)

IS code 4700 9700 14400

Meyerhof’s 2830 7540 10740

PLAXIS 2D 1543 10572 12115

Because of many problems in static field pile load tests,

Dynamic load tests are becoming more common now a days

•Dynamic load testing of piles is a fast and effective method of assessing

foundation bearing capacity that requires instrumenting a deep foundation

with accelerometers and strain transducers and analyzing data collected by

these sensors.

Why Dynamic pile load test required ?

•In addition to bearing capacity, Dynamic Load Testing gives information on

resistance distribution (shaft resistance and end bearing) and evaluates the

shape and integrity of the foundation element.

What is Dynamic pile load test ?

Load Testing

Static Load Testing Dynamic Load Testing

PDA/CAPWAP

Comparison of Dynamic load test

with

Numerical simulation

PILE DYNAMIC TESTING

HAMMER & CRANE STRAIN GAUGE & ACCELEROMETER

Pile Dynamic Analyzer (PDA) : Procedure ( ASTM D4945)

• When hammer strikes the top of a pile,

compression wave travels down the pile.

• The impact induces force F and particle

velocity v (particle displacement *angular frequency).

•The force is computed by the product of

the measured strain signal and pile c/s

area and modulus.

•The velocity is computed by integrating

the measured acceleration

•Force/velocity time histories is captured

by PDA.

RESULTS OBTAINED WITH DYNAMIC LOAD TESTS

CORRELATE WELL WITH THE RESULTS OF STATIC LOAD TEST

0.00

2.00

4.00

6.00

8.00

10.00

0.00 200.00 400.00 600.00 800.00 1,000.00 1,200.00

Sett

lem

ent (

mm

)

Load (kN)

PLAXIS 2D

Static Load Test

Base load by PLAXIS 2D

Skin friction by PLAXIS 2D

• Good Quality Soil Investigation Each Pile Cap n – Aim at Good Core Recovery in Rock & Keep Core box at Pile Loaction

• Prepare Core Log & Select Samples for UCS & Point Load Tests• Have a Geologist at Site for better identification & Classification

of Rock• Design Rock Socket (by consultant)& Specify Termination

Criteria• Consult Equipment Manufacturer for Right Equipment & Tools

and Guideline Method• Procure Quality Accessories & Tools• Client- Consultant- Contractor to Have a Team Approach• Adopt Concrete Coring, Contact Coring, Sonic Logging, PIT, Etc.

for Proof of Quality & Integrity

Proposed Process To Achieve a Good Pile Capacity in Rock

Dr. Naveen BP Ph.D. (IISc) Associate Professor & Head,Department of Civil EngineeringAmity University HaryanaHaryana-122413Mobile No:+91-9916232349Email: bp.naveen864@gmail.com

bpnaveen@ggn.amity.eduWeb: https://sites.google.com/site/bpnaveen864/home