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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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