Pile foundations are commonly used when soil conditions are unsuitable for surface foundations. Piles transfer structural loads deep into the ground until reaching a stratum with sufficient bearing capacity. Piles can be made of concrete, wood, steel, or a composite and are installed by driving, drilling, or jacking into the ground. Pile foundations classify piles based on their material, soil type, and load transmission characteristics. Common pile types include end bearing, friction, and tension piles which transmit vertical, lateral, or uplift loads. Pile capacity and allowable loads are determined through testing and safety factors.

1. BY
CHANDAN K B

2.  Pile foundation is a special kind of deep foundation, where the depth of the
foundation is much greater than the width of the foundation.
 Today, pile foundation is much more common than any other type of deep foundation.
 It is used;
1.where the soil is compressible,
2.where the soil is water logged and
3.when stratum of required bearing
capacity is at greater depth.
The major uses of piles:
 To carry vertical compression loads,
 To resist uplift loads
 To resist horizontal or inclined loads
Pile foundation is required when the soil bearing capacity is not sufficient for the structure to withstand.
This is due to the soil condition or the order of bottom layers, type of loads on foundations, conditions at site
and operational conditions.
Many factors prevent the selection of surface foundation as a suitable foundation such as the nature of soil
and intensity of loads, we use the piles when the soil have low bearing capacity or in building in water like
bridges and dams

3.  A pile foundation consists of two components: Pile cap and
single or group of piles. Piles transfers the loads from
structures to the hard strata, rocks or soil with high bearing
capacity. These are long and slender members whose length
can be more than 15m.
 Piles can be made from concrete, wood or steel depending on
the requirements. These piles are then driven, drilled or
jacked into the ground and connected to pile caps. Pile
foundation are classified based on material of pile
construction, type of soil, and load transmitting characteristic
of piles.

4.  Based on the function;
1. End bearing Pile
2. Friction Pile
3. Compaction Pile
4. Tension Pile or Uplift Pile
5. Anchor Pile
6. Fender Pile and Dolphins
7. Batter Pile
8. Sheet Pile
 Based on the material & composition;
1. Concrete Pile
2. Timber Pile
3. Steel Pile
4. Composite Pile: Concrete & Timber, Concrete & Steel
 Based on the method of installation;
1. Driven Pile
2. Cast-in-situ Pile
3.Driven and cast- in- situ Pile

5. Piles can be divided in to two major categories:
1. End Bearing Piles
If the soil-boring records presence
of bedrock at the site within a reasonable depth,
piles can be extended to the
rock surface
2. Friction Piles
When no layer of rock is present depth at a site,
point bearing piles become very long and
uneconomical. In this type of subsoil, piles
are driven through the softer material to
specified depths.

6. Function of piles
As with other types of foundation, the purpose of a pile foundation is:
To transmit a foundation load to a solid ground
To resist vertical, lateral and uplift load
Piles can be
Timber
Concrete
Steel
Composite
General facts
Usual length: 10m-20m
Usual load: 300kN-3000kN
Advantages
Corrosion resistance
Can be easily combined with a concrete superstructure
Disadvantages
Difficult to achieve proper cutoff
Difficult to transport
Concrete piles

7.  Pile caps carrying very heavy point loads tend to produce high
tensile stresses at the pile cap.
 Reinforcement is thus designed to provide:
◦ Resistance to tensile bending forces in the bottom of the cap
◦ Resistance to vertical shear

8.  Piles are commonly driven by means of a hammer
supported by a crane or a special device known as a
Pile Driver.
Hammers adopted for driving the pile are
of the following types:
1. Drop hammer
2. Single acting hammer
3. Double acting hammer
4. Diesel hammer
5. Vibratory hammer.

9.  What is ultimate load bearing capacity?
 What is allowable load and how is it determined?
 Ultimate load bearing capacity of a pile is defined as
the maximum load which can be carried by a pile and
at which the pile continues to sink without further
increase of the load.
 The allowable load is the safe load which the pile can
carry safely, which can be determined from ultimate
load bearing capacity dividing by suitable F.O.S.

10.  Negative friction is a down-
ward drag acting on a pile
due to the downward mo-
vement of the surrounding
compressible soil relative
to the pile.
 It is shown in figure aside.
 Figure shows the pile pass-
ing through a recently con-
structed cohesive soil fill.
The soil below the fill is
completely consolidated
under its overburden
pressure.

11.  Negative Skin Friction will occur due to the following
reasons:
 When the surrounding compressible soil
has been recently filled.
 If the fill material is loose cohesion less soil.
 By lowering the ground water which increases the
effective stress causing consolidation of the soil with
resultant settlement and friction force being developed
on the pile.
 It also occurs when the fill is over the peat or a soft
clay stratum.

12.  Factors governing the selection of piles
They are:
 Length of the pile in relation to the load and type of soil,
 Characters of structure,
 Availability of the materials,
 Types of loading,
 Factors causing deterioration,
 Ease of maintenance,
 Estimated cost of types of piles, taking into account the initial cost, life expectancy and cost of
maintenance and,
 Availability of funds.
The selection of type of pile foundation is based on site investigation report. Site investigation report
suggests the need of pile foundation, type of pile foundation to be used, depth of pile foundation to
be provided. The cost analysis of various options for use of pile foundation should be carried out
before selection of pile foundation types.
Unless the ground condition is rocks, for heavy construction and multi-storied buildings,
The bearing capacity of soil at shallow depth may not be satisfactory for the loads on the foundation.
In such cases, pile foundation has to be provided. The number of piles in a pile groups required is
calculate from the pile capacity of single pile and the loads on the foundation. Piles are a convenient
method of foundation for works over water, such as jetties or bridge piers.