WACHEMO UNIVERSITY

CENG 4202:
4142: FOUNDATION ENGINEERING II
Instructor: Petros Fekadu 03/2015
 CHAPTER-1
PILE FOUNDATIONS

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 Introduction
• Piles are long and slender members which transfer the load to
deeper soil or rock of high bearing capacity avoiding shallow
soil of low bearing capacity.
• The main components of the foundation are the pile cap and
the piles.

P
I
L
E
weak soil

bed rock
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 BURJ
KHALIFA

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 Uses
When top layers of soil are highly
compressible for it to support structural
loads through shallow foundations
When rock level is shallow enough for end
bearing pile foundations provide a more
economical design
When lateral forces are relatively
prominent.
In presence of expansive and collapsible
soils at the site
In offshore structures
When strong uplift forces on shallow
foundations due to shallow water table can
be partly transmitted to piles
For structures near flowing water (Bridge
abutments, etc.) to avoid the problems due
to erosion 5
 Classification of Piles
Piles can be classified based on:
 Functions
 Effect of installation
 Types of material
 Methods of installation

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 Types of Piles Based on
Function
1. Bearing Piles or End Bearing Piles
2. Friction Piles or Skin Friction Piles
3. Tension Piles or Uplift Piles
4. Anchor Piles
5. Batter Piles
6. Fender Piles
7. Compaction Piles

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 Types of Piles Based on
Function (cont’d)
Bearing Piles
 Driven into the ground until a hard stratum is reached.

 Acts as pillars supporting the super-structure and transmitting the

load to the ground.

 Piles acts as a medium to transmit the load from the foundation

to the resisting sub-stratum.

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 Types of Piles Based on
Function (cont’d)
Friction Piles (Floating Piles)
 Piles are driven at a site where soil is weak or soft to a considerable depth
and it is not economical or rather impossible to rest the bottom end of the pile
on the hard stratum,
 Load is carried by the friction developed between the sides of the pile and the
surrounding ground ( skin friction)
friction)..
 The piles are driven up to such a depth that skin friction developed at the sides
of the piles equals the load coming on the piles
piles..
 Skin friction should be carefully evaluated and suitable factor of safety
applied, as it is this which is supporting the whole of structure over its head.
head.
 The load carrying capacity of friction pile can be increased by-
by-
 increasing diameter of the pile
 driving the pile for larger depth
 grouping of piles
 making surface of the pile rough 9
Types of Piles Based on
Function (cont’d)

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Types of Piles Based on
Function (cont’d)

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 Types of Piles Based on
Function (cont’d)
Anchor Piles
 Piles are used to provide anchorage against horizontal pull from sheet piling
wall or other pulling forces.

Batter piles:
 Piles are driven at an inclination to resist large horizontal and inclined forces.

Fender piles:
 Piles are used to protect concrete deck or other water front structures from the
abrasion or impact caused from the ships or barges.
 Ordinarily made up of timber.

Compaction piles:
 When piles are driven in granular soil with the aim of increasing the bearing
capacity of the soil, the piles are termed as compaction piles.
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Types of Piles Based on
Function (cont’d)

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Types of Piles Based on Their Effect
of Installation

Displacement Piles

Non-Displacement Piles

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Installation of Piles

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 Displacement Piles

Dilatancy: the expansion of cohesionless soils when subject to shearing deformation. 16

Non-Displacement Piles

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Displacement Piles (A/D)

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Non-Displacement Piles (A/D)

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Types of Piles Based on Material

 Steel: H-
H- piles, Steel pipe
 Wood: Timber
 Concrete: Cast
Cast--in
in--situ, Precast or Prestressed
 Composite

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21
 Steel Piles
 Steel piles are usually rolled H shapes or pipe piles.
 H-piles are proportioned to withstand large impact
stresses during hard driving.
 Pipe piles are either welded or seamless steel pipes
which may be driven either open-end or closed-end.
 Pipe piles are often filled with concrete after
driving, although in some cases this is not
necessary.
 The optimum load range on steel piles is 400 to
1200kN.
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 H-PILES

CYLINDERICAL TAPERED 23
Steel Piles (cont’d)

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 Timber Piles
They are tree trunks that have had their branches & barks carefully
trimmed off.

The length of the pile may be 5-15 m. If greater lengths are required,
they may be spliced.

The diameter of the piles at the butt end may vary from 30 to 40 cm.
The diameter at the tip end should not be less than 15 cm.

The usual maximum design load per pile does not exceed 250 kN.

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 Timber Piles
 Used for permanent works in regions where timber is plentiful.

 Timber piles shall be of sound quality and free of defects.

 When a pile is subjected to alternate wetting and drying, the useful life is
relatively short unless treated with a wood preservative.

 After being driven to final depth, all pile heads, treated or untreated, should
be sawn square to sound undamaged wood to receive the pile cap.

 Before concrete for the pile cap is poured, the head of the treated piles should
be protected by a zinc coat, lead paint or by wrapping the pile heads with
fabric upon which hot pitch is applied.

 Driving of timber piles usually results in the crushing of the fibers on the
head (or brooming) which can be somewhat controlled by using a driving cap,
or ring around the butt.
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Timber Piles

Cast iron shoe

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 Timber Piles
 Advantages
 The piles are easy to handle
 Relatively inexpensive where timber is plentiful.
 Sections can be joined together and excess length easily
removed.
 Disadvantages
 The piles will rot above the ground water level. Have a
limited bearing capacity.
 Can easily be damaged during driving by stones and
boulders.
 The piles are attacked by marine borers in salt water.

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 Types of Concrete Piles
Concrete Piles are of 3 types:
 Pre-cast Piles
 Cast in situ Piles
 Prestressed Concrete Piles

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Concrete Piles (cont’d)

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 Concrete Piles (cont’d)
Pre-cast Piles:
 Reinforced concrete piles, molded in circular, square, rectangular
or octagonal form.
 Cast and cured in the casting yard, then transported to the site of
driving.
 If space available it can be cast and cured near the work site.
 Driven in similar manner as timber piles with the help of piles
drivers.
 Diameter normally varies from 35cm to 65cm, length varies
from 4.5m to 30m.

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 Concrete Piles (cont’d)
Pre-cast Piles:
 Function of reinforcement in a pre-cast pile is to resist the
stresses during handling, driving and final loading on the pile
rather than strengthen the pile to act as a column.
 Longitudinal reinforcements usually 20mm to 50mm in diameter,
stirrups 6mm to 10mm in dia.
 For 90 cm length at head and toe, stirrups spacing is 8cm c/c and
for remaining intermediate length it is about 30cm c/c.
 Circular piles are seldom tapered. When tapered piles length is
restricted to 12m.
 A concrete cover of 5cm is maintained throughout, over the main
steel bars.
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 Concrete Piles (cont’d)
Advantages of Pre-cast Piles:
 Very effective
 Simple quality control
 Improves the entire area

Disadvantages of Pre-cast Piles:

 Limited in length
 Difficult to transport
 Not suitable for densely built up area
 Requires costly equipment

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 Concrete Piles (cont’d)
Cast-in-Situ Piles:
 Cast in position inside the ground.
 First of all a bore is dug by driving a casing pipe into the ground.
 Then the soil from the casing is jetted out and filled with cement
concrete after placing necessary reinforcement in it.

Cast-in-situ piles are of two types:

I. Cased Cast-in-Situ Piles: metallic shell is left inside the
ground along with the core
II. Uncased Cast-in-Situ Piles: metallic shell is withdrawn

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 Concrete Piles (cont’d)
Advantages of Cast-in-Situ Concrete Piles:
 Not limited in length
 Can be cast at any place
 Requires less equipment
 Cost is less and is depended on the size

Disadvantages of Cast-in-Situ Concrete Piles:

 Quality control is difficult
 Load carrying is mostly done through end bearing only
 Skin frictional resistance is very low.

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Cast–in-Situ Piles

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 Concrete Piles (cont’d)
Prestressed Concrete Piles
 The greatest disadvantage of large weight and difficulty in
handling of pre-cast pile is eliminated by prestressed concrete
piles.
 The weight is reduced by casting 200mm to 300mm diameter
fiber tubes inside the piles at the time of concreting.
 The pre tensioning cables are subjected to required pull (tension)
in the casting bed.
 The fiber tube is held in position inside the form work and the
piles reinforced with pre stressed cables are concreted in a row.

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 Concrete Piles (cont’d)
Prestressed Concrete Piles
 Prestressed concrete piles are provided with lifting hooks at
1/5th ( 0.2L, L= length of pile ) of pile length from each end.
 Piles length= 50 times the thickness →single point pick up
 More than 50 times the thickness →two point pick up at 0.2L
from either end.
 Pre stressed piles are always pre- cast.

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 Concrete Piles (cont’d)
Advantages of Prestressed Concrete Piles
 It has greater ability to withstand extremely hard driving.
 It is more durable in sea water because of absence of crack.
 It has greater column capacity.
 It has lesser handling costs because of light weight.
 It requires lesser pick-up points.

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 Composite Piles
These piles are combination of different materials in
the same pile.
 Concrete and timber
 Concrete and steel
As indicated earlier, part of a timber pile which is
installed above ground water could be vulnerable to
insect attack and decay.
To avoid decay, concrete or steel pile is used above the
ground water level, whilst wood pile is installed under
the ground water

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 Protecting Timber Piles from
Decay

(b) By extending
pile cap below
water level
(a) By pre-cast
concrete upper
section above
water level.

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 Composite Piles
Advantages
 it is cheap and durable (may reduce foundation cost)
 may solve installation problems.

Disadvantages
 it is difficult to provide a good joint between two dissimilar
materials.

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Composite Piles

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 Classification of Piles Based on Methods of
Installation
(1) Driven Piles
(2) Cast-in-situ Piles
(3) Driven and Cast-in-situ Piles

Driven Piles
These piles are driven in to the soil by applying dropping weight or
dropping hammer.

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 Driven Piles
Advantages:

 Piles can be precast to the required specifications.

 Piles of any size, length and shape can be made in advance
and used at the site. As a result, the progress of the work
will be rapid.
 A pile driven into granular soil compacts the adjacent soil
mass and as a result the bearing capacity of the pile is
increased.
 The work is neat and clean. The supervision of work at the
site can be reduced to a minimum. The storage space
required is very much less.
 Driven piles may conveniently be used in places where it is
advisable not to drill holes for fear of meeting ground water
under pressure.
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 Driven Piles
Disadvantages:

 Precast or pre-stressed concrete piles must be properly reinforced

to withstand handling stresses during transportation 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. This increases the cost of the project.
 Driven piles are not suitable in soils of poor drainage qualities. If
the driving of piles is not properly phased and arranged, there is
every possibility of heaving of the soil or the lifting of the driven
piles during the driving of a new pile.
 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.

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 Cast-in-Situ Piles
 Cast-in-situ piles are concrete piles.
 These piles are distinguished from drilled piers as small
diameter piles.
 They are constructed by making holes in the ground to
the required depth and then filling the hole with
concrete.
 Straight bored piles or piles with one or more bulbs at
intervals may be cast at the site. The latter types are
called under-reamed piles.
 Reinforcement may be used as per the requirements.

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 Cast-in-situ Piles (cont’d)
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.
 These piles are ideally suited in places where
vibrations of any type are required to be avoided to
preserve the safety of the adjoining structure.
 They are suitable in soils of poor drainage qualities
since cast-in-situ piles do not significantly disturb the
surrounding soil.

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 Cast-in-Situ Piles (cont’d)
Disadvantages

 Installation of cast-in-situ piles requires careful

supervision and quality control of all the materials used in
the construction.
 The method is quite cumbersome. 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.
 Construction of piles in holes where there is heavy current
of ground water flow or artesian pressure is very difficult.
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 Driven and Cast-in-Situ Piles
 A steel shell is driven into the ground with the
aid of a mandrel inserted into the shell. The
mandrel is withdrawn and concrete is placed
in the shell. The shell is made of corrugated
and reinforced thin sheet steel or pipes.
 The piles of this type are called a shell type.
The shell-less type is formed by withdrawing
the shell while the concrete is being placed.

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