Pile Foundation

Civil Engineering
Practice
Chapter # 4
Pile Foundation
1
Pile Foundation

CHAPTER # 04
CHP # 04: Pile Foundation
---(Pile Foundation)---
* * *
Piles are relatively long and slender members used to transmit
foundation loads through soil strata of low bearing capacity to
* *
deeper soil or rocky strata having a high bearing capacity.
I th d th l d i l t itt d t th il bIn other words, the load is properly transmitted to the soil by
driving long vertical members of either timber or concrete or
steel called “Piles”.
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Civil engineering practice

Depth at which rocky or hard strata is available can normally be
Depth at which rocky or hard strata is available can normally be
60 to 80 ft, showing the range of depth for the piles.
Piles usually carry excessive loads as load of traffic on a bridge
where the underneath strata can be of sand and silt fully
saturated with watersaturated with water.
Bore logs drawn after soil investigation is used to find out depthg g p
of piles, diameter of piles and the numbers of piles required.
Pile can also be defined as an element of construction placed in
the ground either vertically or slightly inclined to increase the
load carrying capacity of the soil.
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d c y g c p c y s

Piles are required for setting out of towers for high power
Piles are required for setting out of towers for high power
transmission lines and in some cases are also used for supporting
the multistory buildings.
4.1 Types of Piles (Based Upon Use)
1- Sheet Piles
Sheet piling is used primarily to resist lateral pressures such asSheet piling is used primarily to resist lateral pressures such as
flow of water and loose soil. Typical uses include cut-off walls
under dams, cofferdams, trench sheeting, etc.
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2- Load Bearing Piles
These are used primarily to transmit loads through soil
formations with poor supporting properties into or onto
formations that are capable of supporting the loads Dependingformations that are capable of supporting the loads. Depending
upon how load is transferred to the soil, load-bearing piles can
be further classified into:
(a) End Bearing Piles
If l d i i d h il h h h l i h il iIf load is transmitted to the soil through the lower tip, the pile is
called an “End Bearing Pile”.
These piles transmit the superimposed load to stronger strata
such as a rock bed. End area of pile times the bearing capacity of
h k i h l l d hi h b li d
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the rock is the total load, which can be applied.

Considering reasonable factor of safety, we can find diameter of
the pile required.
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(b) Friction Piles
These are designed to transmit the loads by the frictional force
existing between the sides of the pile and the ground such as the
stuff clays or dense sandy depositstuff clays or dense sandy deposit.
Friction can be developed for full length as in first figure or it canp g g
be developed in lower portions only depending upon the
stratification of soil.
Surface area times the safe friction which can be developed per unit
area determines the load to be carried by the pile. Selectingy p g
diameter or length of pile, the other quantity can be calculated.
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(b) Friction Piles
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(c) End Bearing and Friction Piles
These are the piles that dissipate part of the load by friction and
transfer the remaining load to firm strata.
3- Piles as Soil Compactor
Sometimes closely spaced piles are driven to compact theSometimes closely spaced piles are driven to compact the
surrounding soil.
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4.2 Types of Piles (Based on material used and method of
construction)
On the basis of the material from which they are made and the
method of constructing and driving them load bearing pilesmethod of constructing and driving them, load-bearing piles
may be classified as follows:
– Timber
U da. Untreated
b. Treated with a preservative
– Concrete
a. Pre-cast
b. Cast-in-place
S l– Steel
a. I-section
b. Steel-pipe
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p p
– Composite

Driven timber piles, Pacific Highway
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p g y

4.3 Factors Affecting Selection of Piles
Among the factors that will influence the selection of type of piles
for a given project are the following:
1. Type, size, and weight of the structure to be supported.1. Type, size, and weight of the structure to be supported.
2. Physical properties of the soil at the site.
3. Depth to a stratum capable of supporting the piles.
4. Possibility of variations in the depth to a supporting stratum.
5. Availability of materials for piles.
6 Number of piles required6. Number of piles required.
7. Facilities for driving piles.
8. Comparative costs in place.
9. Durability required.
10. Types of structures adjacent to the project.
11 Depth and kind of water if any above the ground into which
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11. Depth and kind of water, if any, above the ground into which
the piles will be driven.

4.4 Significance of Pile Foundation
Pile foundation is suitable for works over water such as
bridge`-piers, foundation of transmission towers and
foundation of multistory buildingsfoundation of multistory buildings.
From head or cap of piles, we can construct the grids with
beams and columns.
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4.4 Significance of Pile Foundation
The number of piles depends on the type of pile and the load
coming from the buildings.
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ooden Pilesooden Piles
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4.5 Wooden Piles
These piles, if used below the ground water level, last for a
very long period but ordinarily they last no longer than 30
years or so even if treated.yea s o so eve t eated.
The circular piles vary in diameter from 12 inch to 16-inch. If
square sizes are used, they also vary in size fro 12 inch to 16-
inch square. The length of the piles is about 20 times the top
width.width.
The timber point may be protected or replaced by a metallic
shoe; shoes are used while driving through soils containing
boulders, gravels, hard clays etc.
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4.5 Wooden Piles
They may be of C.I. and should have sufficient length of
wrought iron straps to connect them with the pile.
The head of the pile is subjected to a heavy impact of the
driving machine; hence, rings of wrought iron are fitted to theg ; , g g
pile head. They vary in cross-section from 2 in. to 4 in.
Timber piles should not be loaded above 15 to 20 tons and
should be carefully driven.
Whenever it is necessary to use a longer pile than available in
usual lengths, it is necessary to splice the piles together, with
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their ends abutting each other.

4.5 Wooden Piles
Additional strength can be obtained by the use of steel
fishplates bolted to the sides of the piles.
Among the advantages of timber piles are the following:
1. The more popular lengths and sizes are available on short
notice.
2. They are economical in cost.
3. They are handled easily, with little danger of breakage.
4. They can be cut off to any desired length after they are driven.
5. They can be pulled easily in the event removal is necessary.
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4.5 Wooden Piles
Among the disadvantages of timber piles are the following:
1. It may be difficult to obtain piles sufficiently long and straight
for some projects.
2. It may be difficult or impossible to drive them into hard
formations.
3 I i diffi l li h i h i l h3. It is difficult to splice them to increase their lengths.
4. While they are satisfactory when used as friction piles, they are
not suitable for use as end-bearing piles under heavy loads.g p y
5. The length of life may be short unless the piles are treated with
a preservative.
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oncrete Pilesoncrete Piles
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4.6 Concrete Piles
(a) Pre-cast Concrete Piles
Square and octagonal piles are cast in horizontal forms, while
round piles are casts in vertical forms.
After the piles are cast, they should be cured for the period
required by specifications, frequently 21 days.
With the exception of short lengths, Precast concrete piles
t b i f d ith ffi i t t l t t dmust be reinforced with sufficient steel to prevent damage or
breakage while they are being handled from the casting beds to
the driving positions.
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4.6 Concrete Piles
( ) P C Pil
Among the advantages of Pre cast concrete piles are theAmong the advantages of Pre-cast concrete piles are the
following:
1. High resistance to chemical and biological attacks.
2. High strength.
3. A pipe may be installed along the center of a pile to facilitate
driving.
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4.6 Concrete Piles
( ) P C Pil
Among the disadvantages of Pre cast concrete piles are theAmong the disadvantages of Pre-cast concrete piles are the
following:
1. It is difficult to reduce or increase the length.
2. Large sizes require heavy and expensive handling and driving
equipment.
3 I bili b i il b h d l h i f3. Inability to obtain piles by purchase may delay the starting of a
project.
4. Possible breakage of piles during handling or driving producesg p g g g p
a delay hazard.
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4.6 Concrete Piles
(b) Cast-in-Place Concrete Piles
These piles are constructed by depositing the freshly mixed
concrete in place in the ground and letting it cure there. The
two principal methods of constructing such piles are:p p g p
1. Driving a metallic shell, leaving it in the ground and filling it
with concrete.
2 D i i t lli h ll d filli it ith t th h ll2. Driving a metallic shell and filling it with concrete as the shell
is pulled from the ground.
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4.6 Concrete Piles
Among the advantages of cast in place concrete piles are theAmong the advantages of cast-in-place concrete piles are the
following:
1. The lightweight shells may be handled and driven easily.
2. Variations in length do not present a serious problem. The
length of a shell may be increased or decreased easily.g y y
3. The shells may be slipped in short lengths and assembled at
the job.
4 E i f i t i t t d b h dli l4. Excess reinforcing, to resist stresses caused by handling only,
is eliminated.
5. The danger of breaking a pile while driving is eliminated.
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6. Additional piles may be provided quickly if they are needed.

4.6 Concrete Piles
Among the disadvantages of cast-in-place concrete piles are the
following:
1. A slight movement of the earth around an un-reinforced pile
may break it.
2. An uplifting force, acting on the shaft of an uncased and un-
reinforced pile, may cause it to fail in tension.
3 Th b tt f il t b t i l3. The bottom of pile may not be symmetrical.
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teel Pilesteel Piles
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4.7 Steel Piles
Steel piles may be of I-section or hollow pipe section 10 inches
t 24 i h di t ith 3/8 i h thi kto 24 inches diameter with 3/8 inches thickness.
Because of a small sectional area steel piles are easy to driveBecause of a small sectional area, steel piles are easy to drive.
The pipes are driven with open ends. Compressed air with a
pressure of 100 psi in a 2½ inches or more diameter pipe and
h f ili h d i ithus facilitates the driving.
These piles are later on filled with concrete Steel piles areThese piles are later on filled with concrete. Steel piles are
mostly used as end bearing piles because of their less available
surface area to take the loads by frictional forces.
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4.7 Steel Piles
In constructing foundations that require piles driven to great
depths, steel I-section probably are more suitable than anydept s, stee sect o p obab y a e o e su tab e t a a y
other type.
Steel piles may be driven through hard materials to a specified
depth to eliminate the danger of failure due to scouring, such
as under a pier in a river.as under a pier in a river.
Also, steel piles may be driven to great depths through poor
soils to bear on a solid rock stratum.
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4.7 Steel Piles
The great strength of steel combined with the small
displacement of soil permits a large portion of the energy fromd sp ace e t o so pe ts a a ge po t o o t e e e gy o
a pile hammer to be transmitted to the bottom of a pile.
As a result, it is possible to drive steel piles into soils, which
could not be penetrated by any other type of pile.
By weld splicing sections together, lengths in excess of 200ft
have been driven.
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crew Pilescrew Piles
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4.8 Screw Piles
Screw piles consist of iron or steel shaft
h i t it d t i t t lhaving at its end a cast iron or cast steel
screw, with a blade 1.5ft to 5ft in diameter.
These piles can be screwed down to a
great depth in clay, etc., and penetrate
h h ll b kthrough small broken stones.
The base area of the screw does most ofThe base area of the screw does most of
the weight bearing; they can be used for
bridges in riverbeds with deep clay
f d i
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foundation.

4.9 Pile Driving
The operation of forcing a pile into ground without any
previous excavation is called “Pile Driving”.
Following are the various methods of pile driving:
1. Drop hammer.
2. Steam-hammer.
3 Boring3. Boring.
4. Screwing.
5. Water jet.
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4.9 Pile Driving
1 D H M h d
1- Drop Hammer Method
It is the simplest method of pile driving. In this method, at s t e s p est et od o p e d v g. t s et od, a
hammer is dropped on the head of the pile and is guided
during its fall by suitable staging.
The hammer is raised by pulling a rope manually or by steam
engine or electric motor. The weight of the hammer forengine or electric motor. The weight of the hammer for
driving concrete or wooden piles is about 225 kg for short
piles and 900 kg to 2350 kg for long and heavy piles.
Hammer is generally dropped from a height of 15m to 45m
and the height is limited to 6 m The pile-driving frame is kept
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and the height is limited to 6 m. The pile driving frame is kept
in vertical position by suitable ropes.

4.9 Pile Driving
2 S H M h d
2- Steam Hammer Method
A heavy hammer is dropped on to the pile through a smalleavy a e s d opped o to t e p e t oug a s a
height but in quick succession. Single acting or double acting
steam hammers are available.
These hammers are raised with high-pressure steam and are
dropped under gravity when single acting or by steam wheredropped under gravity when single acting or by steam where
there is double acting hammer. These hammers are specially
used for driving sheet piles and where small vibrations are
i d t b t i th ilrequired to be set up in the piles.
Special devices are used to protect the heads of the piles from
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Special devices are used to protect the heads of the piles from
damage due to excessive blows, which they receive.

4.9 Pile Driving
3- Boring
S ti ili i d b b i h l f it bl di tSometimes, piling is done by boring holes of suitable diameter
to the required depth and then dropping piles in them.
Generally cast-in-situ piles are laid by this method.
4- Screwing
Screw piles and disc piles are generally driven by this method.
They are driven into the ground by turning them round andThey are driven into the ground by turning them round and
round in one direction with big levers.
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4.9 Pile Driving
5 W J
5- Water Jets
Pile driving can also be done by displacing the material at orP e d v g ca a so be do e by d sp ac g t e ate a at o
near the foot of the pile by means of one or more water jets
under pressure.
Sometimes, hammer may be used to force the pile rapidly into
the ground. The pressure of the jet should be sufficient tothe ground. The pressure of the jet should be sufficient to
displace the soil and other removed materials for driving the
piles quickly and satisfactorily.
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