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PILE FOUNDATION

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Brief Outline

DEFINITION OF PILE

CLASSIFICATION OF PILE

PILE CAPACITY

SETTLEMENT OF PILES AND PILE GROUP

LATERAL LOADED PILES (Seismic

Consideration)

SUMMARY

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Piles What?

Piles are columnar elements in a

foundation which have the function of

transferring load from the superstructure

through weak compressible strata orthrough water, onto stiffer or more compact

and less compressible soils or onto rock.

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Piles When?

When the strata at or just below the ground surface is highlycompressible and very weak to support the load transmittedby the structure.

When the plan of the structure is irregularrelative to itsoutline and load distribution.

for the transmission of structural loads through deep watertoa firm stratum.

to resist horizontal forces in addition to support the verticalloads.

when the soil conditions are such that a wash out, erosion orscour of soil may occur from underneath a shallowfoundation.

To resist uplift forces - transmission towers, off-shoreplatforms

expansive soils - swell or shrink as the water contentchanges.

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Some Examples

Multistoried Building Resting on Piles

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Some Examples

Piles Used to Resist Uplift

Forces

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Some Examples

Piles used to Resist lateral

Loads

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Classification of Piles

Based on Material

Steel Piles, Concrete Piles, Timber Piles, Composite Piles.

Based on Load Transfer

End Bearing Piles, Friction Piles, Combined End bearing and Friction

Piles Based on Method of Installation

Driven Piles, Driven Cast-in-situ Piles, Bored and Cast-in-situ Piles,Screw Piles, Jacked Piles.

Based on Use

Load Bearing Piles, Compaction Piles, Sheet Piles, Fender Piles,Anchor Piles.

Based on Displacement of Soil

Displacement Piles, Non-Displacement Piles.

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Selection of Piles

Length of pile in relation to the load and type ofsoil

Character of structure

Availability of materials

Type of loading

Factors causing deterioration

Ease of maintenance

Estimated costs of types of piles, taking intoaccount the initial cost, life expectancy and

Cost of maintenance

Availability of funds

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Load Transfer Mechanism

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Load Transfer Mechanism

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Types of Failure of Piles

Buckling in very weak surrounding soil

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Types of Failure of Piles

General Shear Failure in Strong Lower Soil

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Types of Failure of Piles

Soil of Uniform Strength

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Types of Failure of Piles

Low Strength Soil in Lower Layer, Skin Friction

Predominates

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Types of Failure of Piles

Skin Friction in Tension

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Carrying Capacity of Piles

Using Theory (c,)

Using SPT value

Using SCPT Value

Using Dynamic Formula

Pile Load Test

Static Formula

In-situ Penetration Tests

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STATIC METHOD

DNqNcNq

AfAqQ

QQQ

qcp

ssppu

fpu

2

1

Qu = Ultimate failure load

Qp or Qb = Point (base or tip) resistance Qs = Shaft resistance developed by friction (or adhesion)

between the soil and the pile shaft

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STATIC METHOD FOR DRIVEN

PILES IN SAND

End Bearing Capacity

Frictional Resistance

Ultimate Load

n

i

isivbqu

svbqu

vhs

qp

qp

AKAqNQ

AKAqNQ

Kf

qNq

DNqNq

1

tan

tan

tantan

2

1

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STATIC METHOD FOR DRIVEN

PILES IN CLAY

End Bearing Capacity

Frictional Resistance

Net Ultimate Loadssbcu

sss

cp

cp

AfAcNQ

AfQ

cNq

qcNq

Net Bearing Capacity

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Problem 1

A concrete pile of 45 cm diameterwas driven into sand of loose tomedium density to a depth of 15m.The following properties are

known:(a) Average unit weight of soil along

the length of the pile, y = 17.5kN/m3 , average = 30,

(b) average Ks = 1.0 and= 0.750.Calculate (a) the ultimate bearingcapacity of the pile, and (b) theallowable load with Fs = 2.5.Assume the water table is at great

depth.

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Solution

Qu = 1841 kN

Qa = 736 kN

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Problem 2

Assume in Ex. 1 that the water table is at theground surface and

sat= 18.5 kN/m3. All the

otherdata remain the same. Calculate Qu andQa.

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Solution

Qu = 914 kN

Qa = 366 kN

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Calculation of Qb and Qf

Vesic

Tomlinson

Berezantsev

Meyerhof

Janbu

Coyle and Castello

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STATIC METHOD FOR BORED

PILES IN SAND

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Driven Piles - Advantages

Piles ofany size, length and shape can be made inadvance and used at the site. rapid progress of work

Driven into granular soil - compacts the adjacent soilmass - increase in bearing capacity

The work is neat and clean Supervision of work at the site can be reduced to a

minimum.

Storage space required is very much less.

In places where it is advisable not to drill holes for fearof meeting ground water under pressure.

Forworks over watersuch as piles in wharf structuresor jetties.

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Driven Piles - Disadvantages

Must be properly reinforced to withstand handlingstresses during transportation and driving.

Advance planning is required for handling and driving.

Requires heavy equipment for handling and driving.

Since the exact length required at the site cannot bedetermined in advance, the method involves cuttingoff extra lengths or adding more lengths - increasedcost of project

Driven piles are not suitable in soils of poor drainage

qualities Soil heaving or lifting Where the foundations ofadjacent structures are

likely to be affected due to the vibrations generated bythe driving of piles, driven piles should not be used.

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Bored Piles - Advantages

Piles ofany size and length may be

constructed at the site.

Damage due to driving and handling that is

common in precast piles is eliminated in thiscase.

Ideally suited in places where vibrations of any

type are required to be avoided to preserve thesafety of the adjoining structure.

suitable in soils of poor drainage qualities

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Bored Piles - Disadvantages

Requires careful supervision and qualitycontrol of all the materials used in theconstruction.

It needs sufficient storage space forall thematerials used in the construction.

The advantage ofincreased bearing capacitydue to compaction in granular soil that could

be obtained by a driven pile is not produced bya cast-in-situ pile.

where there is heavy current of ground waterflow or artesian pressure - very difficult to

construct

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Based on SPT Values

Displacement piles

For H- piles

Bored Piles

Where

Qu ultimate total load in kN

Ncor average corrected SPTvalue

below pile tip

corrected average SPTvalue

along the pile shaft

Ab base area of pile in m2

(for H-piles including the soilbetween the flanges)

As shaft surface area in m2

scorbcoru

corcorb

scorbcoru

scorbcoru

fbu

ANANQ

N

d

LNqwhere

ANAd

LNQ

ANAd

LNQ

QQQ

67.0133

40040,

40

240

corN

B i C it b d

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Bearing Capacity based on

SCPT

Vander Veen's method

Schmertmann's method

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VanderVeens Method

Ultimate load capacity of pile

Pile base resistance,

Ultimate skin friction

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Schmertmann's method

Pile base resistance

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Ulti t Ski L d C h i l

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Ultimate Skin Load - Cohesionless

Soil

Ulti t Ski L d C h i l

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Ultimate Skin Load - Cohesionless

Soil

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