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A introduction to piling foundations
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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