Introduction to pile foundations, conditions under which piles are provided and types of piles

1. AXIALLY LOADED
PILE FOUNDATIONS
- Rohan Dasgupta

2. INTRODUCTION
When the soil at or near the ground surface is not capable
of supporting a structure, pile foundations are required to transfer
the loads to deeper strata.
Pile foundations are, therefore, used when surface soil is
unsuitable for shallow foundations and a firm stratum is so deep
that it cannot be reached economically by a shallow foundation.

3. INTRODUCTION
A pile is a slender
structural member made of
concrete, steel or wood .
A pile is either driven
into the soil or formed in-situ
by excavating a hole and filling
it with concrete.
A cast-in situ pile with a
diameter greater than 0.6 m is
known as a pier.

4. INTRODUCTION: ECONOMY
A pile foundation is generally more costly than a shallow
foundation.
It should be adopted only and only when shallow
foundation is not feasible.
In certain situations, a fully compensated floating raft
maybe more economical than a pile foundation.
In some cases, the soil is improved by various methods to
make it suitable for a shallow foundation.

5. NECESSITY OF PILE FOUNDATIONS:
Pile foundations are used in the following conditions:
1. When the strata at or below the ground surface is highly
compressible and very weak to support the load transmitted
by the structure.
2. When the plan of the structure is irregular relative to its
outline and load distribution. It would cause non-uniform
settlement if a shallow foundation is constructed. A pile
foundation is required to reduce differential settlement.
3. Pile foundations are required for the transmission of structural
loads through deep water to a firm stratum.
continued...

6. NECESSITY OF PILE FOUNDATIONS: continued...
4. Pile foundations are used to resist horizontal forces in addition
to support the vertical loads in earth retaining structures and
tall structures that are subjected to horizontal forces due to
wind or earthquake.
5. Piles are required when the soil conditions are such that a
washout, erosion or scour of soil may occur from underneath a
shallow foundation.
6. Piles are used for the foundations of some structures, such as
transmission towers, off-shore platforms etc. which are
subjected to uplift.
continued...

7. NECESSITY OF PILE FOUNDATIONS: continued...
7. In case of expansive soils, such as black cotton soil, which
swell or shrink as the water content changes, piles are
preferred to transfer the loads below the active zones.
8. Collapsible soils, such as loess, have a breakdown of structure
accompanied by a sudden decrease in void’s ratio when there
is an increase in water content. Piles are used to transfer the
load beyond the zone of possible moisture changes in such
soils.

8. Q. 6. a) What are the conditions where a pile foundation is more
suitable than a shallow foundation?
(Dec 2014; 5 marks)

12. CLASSIFICATION OF PILES
Materials
Used
Steel Piles
Concrete Piles
Timber Piles
Composite
Piles
Mode of
Transfer of
Loads
End Bearing
Piles
Friction Piles
Combined Piles
Methods
of
Installatation
Driven Piles
Driven & Cast-in-
Situ Piles
Bored & Cast-in-
Situ Piles
Screw Piles
Jacked Piles
Use
Load Bearing
Piles
Compaction
Piles
Tension Piles
Sheet Piles
Fender Piles
Anchor Piles
Displacement
of
Soil
Displacement
Piles
Non-Displacement
Piles
on the basis of

13. CLASSIFICATION OF PILES: MATERIALS USED
Steel Piles

14. CLASSIFICATION OF PILES: MATERIALS USED
• STEEL PILES are generally either in the form of thick pipes or rolled
steel H-sections.
• Pipe steel piles are driven into the ground with their ends open or
closed.
• Piles are provided with a driving point or shoe at the lower end.
• Epoxy coatings are applied in the factory during manufacture of pipes
to reduce corrosion of the steel piles.
• Sometimes concrete encasement at site is done as a protection
against corrosion.
• To take into account the corrosion, an additional thickness of the steel
section is usually recommended.

15. CLASSIFICATION OF PILES: MATERIALS USED
Concrete Piles

16. CLASSIFICATION OF PILES: MATERIALS USED
• Cement concrete is used in the construction of concrete piles.
• Concrete piles are either precast or cast-in-situ.
• Precast concrete piles are prepared in a factory or casting yard.
• The reinforcement is provided to resist handling or driving
stresses.
• Precast piles can also be prestressed using high strength steel
pretensioned cables.
• A cast-in-situ pile is constructed by making a hole in the ground
and then filling it with concrete.
• A cast-in-situ pile may be cased or uncased.
• A cased pile is constructed by driving a steel casing into the
ground and then filling it with concrete.
• An uncased pile is constructed by driving the casing into the
ground to a desired depth and gradually withdrawing the casing
when fresh concrete is filled.

17. CLASSIFICATION OF PILES: MATERIALS USED
Timber Piles

18. CLASSIFICATION OF PILES: MATERIALS USED
• Timber piles are made of tree trunks after proper trimming.
• The timber used should be straight, sound and without defects.
• Steel shoes are provided to prevent damage during driving.
• To avoid damage to the top of the pile, a metal band or cap is
provided.
• Splicing of timber piles is done using a pile sleeve or metal straps and
bolts.
• The length of the pipe sleeve should be at least 5 times the diameter
of the timber pile.
• Timber piles below the water table have generally long lives.
• However, above the water table, they are attacked by insects.
• The life of a timber pile may be increased by preservatives like
creosote oils.
• Timber piles should not be used in marine environments where these
are attacked by various organisms.

19. CLASSIFICATION OF PILES: MATERIALS USED
Composite Piles

20. CLASSIFICATION OF PILES: MATERIALS USED
• Composite piles are made of two materials.
• A composite pile may consist of the lower portion of steel and upper
portion of cast-in-situ concrete.
• A composite pile may also have the lower portion of timber below the
permanent water table and the upper portion of concrete.
• As it is difficult to provide a proper joint between two dissimilar
materials, composite piles are rarely used in practice.

21. CLASSIFICATION OF PILES: MODE OF LOAD TRANSFER
• End bearing piles transmit the load through their bottom tips.
• Such piles act as columns and transmit the load through a weak
material to a firm stratum below.
• If bed rock is located within a reasonable depth, piles can be
extended to the rock.
• The ultimate capacity of the pile depends upon the bearing capacity
of the rock.
• If instead of bed rock, a fairly compact and hard stratum of soil exists
at a reasonable depth, piles can be extended a few metres into the
hard stratum.
• End bearing piles are also known as point-bearing piles.
• The ultimate load carrying capacity
Qu is equal to the load carried by the
point or the bottom end QP

22. CLASSIFICATION OF PILES: MODE OF LOAD TRANSFER
• Friction piles do not reach the hard stratum.
• These piles transfer the load through skin friction between the
embedded surface of the pile and the surrounding soil.
• Friction piles are used when the hard stratum is not available at a
reasonable depth.
• Friction piles are also known as floating piles as they do not reach
the hard stratum.
• The ultimate load carrying capacity Qu is equal to the load transferred
by skin friction QS.
• Note: The term “friction pile” is
a misnomer, as in clayey soils,
the load is transferred by
adhesion and not friction
between pile surface and the
soil.

23. CLASSIFICATION OF PILES: MODE OF LOAD TRANSFER
• Combined End Bearing and Friction piles transfer loads by a
combination of end bearing at the bottom of the piles and friction
along the surface of the pile shaft.
• The ultimate load carrying capacity Qu by the pile equal to the sum of
the load carried by the pile point QP and the load carried by skin
friction QS

24. Driven Piles
Driven and Cast-in-Situ Piles
Screw Piles
Bored and Cast-in-Situ Piles
Methods
of
Pile
Installation

25. CLASSIFICATION OF PILES: METHOD OF INSTALLATION
• Driven piles are driven into the soil by applying blows of a heavy
hammer on their tops.
• Driven and cast-in-situ piles are formed by driving a casing with a
closed bottom end into the soil. The casing is later filled with concrete.
The casing may or may not be withdrawn.
• Bored and cast-in-situ piles are formed by excavating a hole into the
ground and then filling it with concrete.
• Screw piles are screwed into the soil.
• Jacked piles are jacked into the soil by applying a downward force
with the help of a hydraulic jack.

26. Fender Piles
Sheet Piles
Compaction
Piles
Tension Piles

27. CLASSIFICATION OF PILES: USE
• Load bearing piles are used to transfer the load of the structure to a
suitable stratum by end bearing or friction or both.
• Compaction piles are driven into loose granular soils to increase the
relative density. The bearing capacity of the soil is increased due to
densification caused by vibrations.
• Tension piles are used to anchor down structures subjected to
hydrostatic uplift forces or overturning forces.
• Sheet piles form a continuous wall or bulkhead which is used for
retaining earth or water.
• Fender piles are sheet piles which are used to protect water-front
structures from impact of ships and vessels.
• Anchor piles are used to provide anchorage for anchored sheet piles.

28. CLASSIFICATION OF PILES: DISPLACEMENT OF SOIL
• Displacement piles are the piles which
displaces the soil laterally when they are
installed. The soil gets densified. The
installation may cause heaving of
surrounding ground. Precast concrete pile
and closed-end piles are high
displacement piles. Steel H-piles are low
displacement piles. All driven piles are
displacement piles.
• Non-displacement piles are the piles
where soil is removed when the hole is
bored. There is no displacement of the
soil during installation. This causes very
little change in the stresses in the
surrounding soil. All bored piles are non-
displacement piles.

29. Q. 1. c) Explain pile foundations on the basis of load transfer and the
method of installation.
(May 2014, 5 marks)
Q. 5. a) Explain pile foundations on the basis of material, influence
of pile installation, load transfer and method of installation.
(May 2014, 10 marks)
Q. 6. c) Classify driven piles according to the function of soil. Support
the answer with proper figure.
(Dec 2015; 5 marks)
Q. 4. a) Classify piles based on method of installation.
(Dec 2012, 10 marks)

30. CONSTRUCTION METHODS OF DRIVEN PILE
The following methods are commonly used:
1. Hammer Driving 2. Vibratory Pile Driving
3. Jetting Techniques 4. Partial Augering Method

31. CONSTRUCTION METHODS OF DRIVEN PILE: HAMMER DRIVING
HOIST MECHANISM

32. CONSTRUCTION METHODS OF DRIVEN PILE: HAMMER DRIVING
The following types of hammers are commonly used:
1. Drop Hammer 2. Single Acting Hammer
3. Double Acting Hammer 4. Diesel Hammer
HOIST MECHANISM

33. CONSTRUCTION METHODS OF DRIVEN PILE: HAMMER DRIVING
• Drop hammer: If a hammer is raised by winch and allowed to fall by
gravity on the top of the pile, it is called a drop hammer.
• Single acting hammer: If a hammer is raised by steam or compressed air
or internal combustion, but it allowed to fall by gravity alone it is called a
single acting hammer.
• Double acting hammer: If a hammer is raised by steam or compressed
air or internal combustion, and the same technique is used for the fall as
well, it is called a double acting hammer.
• Diesel hammer is a small, light weight self contained and self acting
type of hammer using gasoline or diesel as a fuel.