A introuduction to Piling foundations.

PILE FOUNDATION

Brief Outline

DEFINITION OF PILE

CLASSIFICATION OF PILE

PILE CAPACITY

SETTLEMENT OF PILES AND PILE GROUP

LATERAL LOADED PILES (Seismic Consideration)

SUMMARY

Piles – What? Piles are columnar elements in a

foundation which have the function of transferring load from the superstructure through weak compressible strata or through water, onto stiffer or more compact and less compressible soils or onto rock.

Piles – When? When the strata at or just below the ground surface is highly

compressible and very weak to support the load transmitted by the structure.

When the plan of the structure is irregular relative to its outline and load distribution.

for the transmission of structural loads through deep water to a firm stratum.

to resist horizontal forces in addition to support the vertical loads. when the soil conditions are such that a wash out, erosion or

scour of soil may occur from underneath a shallow foundation. To resist uplift forces - transmission towers, off-shore platforms expansive soils - swell or shrink as the water content changes. Collapsible soils

Some Examples

Multistoried Building Resting on Piles

Some Examples

Piles Used to Resist Uplift Forces

Some Examples

Piles used to Resist lateral Loads

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.

Selection of Piles Length of pile in relation to the load and type of soil Character of structure Availability of materials Type of loading Factors causing deterioration Ease of maintenance Estimated costs of types of piles, taking into

account the initial cost, life expectancy and Cost of maintenance Availability of funds

Load Transfer Mechanism

Load Transfer Mechanism

Types of Failure of Piles

Buckling in very weak surrounding soil

Types of Failure of Piles

General Shear Failure in Strong Lower Soil

Types of Failure of Piles

Soil of Uniform Strength

Types of Failure of Piles

Low Strength Soil in Lower Layer, Skin Friction Predominates

Types of Failure of Piles

Skin Friction in Tension

Carrying Capacity of Piles

Using Theory (c,φ) Using SPT value Using SCPT Value Using Dynamic Formula Pile Load Test

Static Formula

In-situ Penetration Tests

STATIC METHOD

DNqNcNq

AfAqQ

QQQ

qcp

ssppu

fpu

21

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

STATIC METHOD FOR DRIVEN PILES IN SAND

End Bearing Capacity

Frictional Resistance

Ultimate Load

n

iisivbqu

svbqu

vhs

qp

qp

AKAqNQ

AKAqNQ

Kf

qNq

DNqNq

1

tan

tan

tantan

21

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

Problem 1 A concrete pile of 45 cm diameter

was driven into sand of loose to medium density to a depth of 15m. The following properties are known:

(a) Average unit weight of soil along the length of the pile, y = 17.5 kN/m3 , average φ = 30°,

(b) average Ks = 1.0 and δ= 0.750.Calculate (a) the ultimate bearing capacity of the pile, and (b) the allowable load with Fs = 2.5. Assume the water table is at great depth.

Solution Qu = 1841 kN Qa = 736 kN

Problem 2 Assume in Ex. 1 that the water table is

at the ground surface and γsat= 18.5 kN/m3. All the other data remain the same. Calculate Qu and Qa.

Solution Qu = 914 kN Qa = 366 kN

Calculation of Qb and Qf

Vesic Tomlinson Berezantsev Meyerhof Janbu Coyle and Castello

Thank you

STATIC METHOD FOR BORED PILES IN SAND

Driven Piles - Advantages Piles of any size, length and shape can be made in

advance and used at the site. – rapid progress of work Driven into granular soil - compacts the adjacent soil

mass - 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 fear

of meeting ground water under pressure. For works over water such as piles in wharf structures

or jetties.

Driven Piles - Disadvantages Must be properly reinforced to withstand handling

stresses 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 be

determined in advance, the method involves cutting off extra lengths or adding more lengths - increased cost of project

Driven piles are not suitable in soils of poor drainage qualities – Soil heaving or lifting

Where the foundations of adjacent structures are likely to be affected due to the vibrations generated by the driving of piles, driven piles should not be used.

Bored Piles - Advantages Piles of any size and length may be

constructed at the site. Damage due to driving and handling that is

common in precast piles is eliminated in this case.

Ideally suited in places where vibrations of any type are required to be avoided to preserve the safety of the adjoining structure.

suitable in soils of poor drainage qualities

Bored Piles - Disadvantages Requires careful supervision and quality control of

all the materials used in the construction. It needs sufficient storage space for all the

materials used in the construction. The advantage of increased bearing capacity due

to compaction in granular soil that could be obtained by a driven pile is not produced by a cast-in-situ pile.

where there is heavy current of ground water flow or artesian pressure - very difficult to construct

Based on SPT Values Displacement piles

For H- piles

Bored Piles

WhereQu ultimate total load in

kNNcor average corrected SPT value below pile tip

corrected average SPT value

along the pile shaftAb base area of pile in

m2 (for H-piles including the soil

between the flanges)As shaft surface area in m2

scorbcoru

corcorb

scorbcoru

scorbcoru

fbu

ANANQ

NdLNqwhere

ANAdLNQ

ANAdLNQ

QQQ

67.0133

40040,

40

240

corN

Bearing Capacity based on SCPT Vander Veen's method Schmertmann's method

Vander Veen’s Method Ultimate load capacity of pile

Pile base resistance,

Ultimate skin friction

Schmertmann's method Pile base resistance

Ultimate Skin Load - Cohesionless Soil

Ultimate Skin Load - Cohesionless Soil