2. Syllabus
• PILE FOUNDATION: Classification and types of piles,
constructional features of cast–in–situ & pre-cast concrete
piles,
• pile driving methods, effect of pile driving on ground, load
transfer mechanism of axially loaded piles. Pile capacity by
• Static formula & Dynamic formula, pile load test and
interpretation of data, group action in piles, spacing of piles in
• groups, group efficiency, overlapping of stresses, settlement
of pile group by simple approach, negative skin friction
• and its effect on pile capacity, general feature of under
reamed piles,
• Introduction to well foundations, caissons and
• coffer dams.
3. • 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
• 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.
5.
6.
7. Necessity of pile foundation
1) When the strata at or just 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 . Pile
foundation is required to reduce differential settlement
3) Pile foundation are required for the transmission of
structural loads through deep water to a firm stratum.
4) Pile foundations are used to resist horizontal forces in
addition to support the vertical loads in earth-retaining
structure and tall structure that are subjected to horizontal
forces due to wind and earthquake.
5) Pile are required when the soil condition are such that a
wash out, score of soil may occur from underneath
foundation.
8. 6) Piles are used for the foundation of some structure, such as
transmission towers, off-shore platform, which are subjected
to uplift.
7) In case of expansive soils, such as black cotton soil, which
swell or shrink as the water content changes, piles are used to
transfer the load below the active zone.
8) Collapsible soils, such as loess, have a breakdown of structure
accompanied by a sudden decrease in void 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.
9. • Function of Pile Foundation:
As other types of foundations, the purpose of pile foundations is:
1) To transmit the buildings loads to the foundations and the ground soil layers
whether these loads vertical or inclined
2) To install loose cohesion less soil through displacement and vibration.
3) To control the settlements; which can be accompanied by surface
foundations.
4) To increase the factor of safety for heavy loads buildings
• 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.
10. Classification of soil
• 1)Classification according to material used
i)Steel Pile ii) Concrete Pile iii) Timber Pile iv) Composite Pile
• 2) Classification based on mode of Transfer of loads
i) End bearing pile ii) Friction pile iii) Combined end bearing &
Friction pile
• 3)Classification based on method of installation
i)Driven pile ii) Driven & caste-in situ pile iii) Boared and cast-in-
situ pile iv) Screw pile v) Jacked piles
• 4)Classification based on use/function
i) Load bearing pile ii) Compaction pile iii) Tension pile iv) Sheet
pile v) Fender pile vi) Anchor pile
• 5)Classification based on displacement of soil
i) Displacement pile ii) Non-Displacement pile
11. 1)Classification according to material used
i)Steel Pile:- 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 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.
ii) Concrete Pile :- Cement concrete is used in the construction of concrete
pile. Concrete piles are either precast or caste in situ. Precast concrete
piles are prepared in a factory or a casting yard. The reinforcement is
provided to resist handling and driving stresses . Precast piles can also
be prestressed using high strength steel pretensioned cables.
A caste-in situ pile is constructed by making a hole in the ground
and then filling it with concrete. A caste in situ pile may be cased or
uncased. A cased pile is constructed by driving a steel casing into the
ground and filling it with concrete . An uncased pile is constructed by
driving the casing to the desired depth and gradually withdrawing casing
when fresh concrete is filled. An uncased pile may have a pedestal.
12. iii) Timber Pile:- Timber piles are made from tree trunks after proper
trimming . The timber used should be straight, sound and free
from defects. Steel shoes are provided to prevent damage during
driving. To avoid damage to the top of pile, a metal band or cap is
provided. Splicing of timber pile is done using a pipe sleeve or
metal straps and bolts. The length of the pipe sleeve should be at
least five times the diameter of pile.
Timber pile below the water table have generally long life. However,
above the water table, these are attacked by insects . The life of
the timber pile can be increased by preservatives such as creosote
oil. Timber piles should not be used in marine environment where
these are attacked by various organisms.
iv) Composite Pile:- A composite pile is made of two materials. A
composite pile may consist of the lower portion of caste-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 material, composite piles are rarely used in
practice.
13. 2) Classification based on mode of Transfer of loads
• i) End bearing pile
• Also called as point-bearing piles are selected when the
depth of hard soil strata or bedrock at site is within
reasonable depth. The length of pile to be used can be easily
computed based on bedrock depth obtained from soil
exploration borehole records.
• In this case, the loads from structures are directly
transferred the hard soil through bearing action of pile
bottom tip and it does not require the use of skin friction to
resist loads. The cost of construction of piles in such cases is
optimum.
• The ultimate capacity of pile or pile group depends on the
bearing capacity of bedrock or hard strata. Number of piles
to be used in this case depends on the loads from structure
and individual capacity of piles.
14. • In this case,
• QU = QP
• Where QU is the ultimate load capacity of pile foundation
• QP is the load carried by the end bearing pile or pile group.
• In case when the hard bedrock is not available at reasonable
depth and fairly compacted hard strata of soil exists, then
piles should be extended a few meters into the hard soil
strata.
15. End Bearing Piles
ROCK
SOFT SOIL
PILES
End bearing pile rests on a relative firm
soil . The load of the structure is
transmitted through the pile into this
firm soil or rock because the base of
the pile bears the load of the structure,
this type of pile is called end bearing
pile
Most of the piles used in
Hong Kong are end bearing
piles. This is because the
majority of new
developments are on
reclaimed land
16. Friction Pile
• Friction piles resist the loads from structures due its skin
friction with soil. This type of pile foundation is selected
when a hard stratum is available at large depth and
construction of end bearing pile becomes uneconomical.
Then number of piles in a group is selected to resist the load
from structure through its skin friction. This type of pile
foundation also resists loads due to end bearing but its value
is small, thus it is neglected in calculation.
• The length of friction pile to be selected in this case depends
on the shear strength of soil, loads from structures and size
of piles. The capacity of individual pile is calculated based on
skin friction resistance provided by selected length of pile.
Optimum length of this pile should be used considering
economy. The number of piles required in a group can be
calculated from individual pile capacity.
17. • In this case,
• QU = QS
• Where QU is the ultimate load capacity of pile foundation
QS is the load carried by the friction pile or pile group.
The load is transferred to the soil through friction in case of
sandy soil and adhesion in case of clayey soil. Loose sand
and soft clays may not provide sufficient skin friction or
adhesion resistance to heavy loads from structures.
18. SOFT SOIL
PILES
Friction Piles
If the firm soil is at a considerable
depth, it may be very expensive to
use end bearing piles. In such
situations, the piles are driven
through the penetrable soil for
some distance. The piles transmit
the load of structure to the
penetrable soil by means of skin
friction between the soil.
19. ii) Friction pile
• The use of pile foundations as load carrying and load transferring
systems has been for many years. Timber piles were used in early
days, driven in to the ground by hand or holes were dug and filled
with sand and stones. The use of steel pile started since 19th
century and concrete piles since 20th century.
• With the change in technology and industrial revolution, many
advance systems have been developed for pile driving from the
invention of steam and diesel pile driving machines.
• The use of pile foundations is increasing day by day due to non-
availability of land for construction. Heavy multi-storyed building
are being constructed, and load from these structures can not be
directly transferred to ground due to low bearing capacity issue
and stability issues of building during lateral load application. So,
demand for use of pile foundations are increasing day by day. Due
to this demand for piles, there have been many improvements in
piles and pile driving technology and systems. Today there are
many advanced techniques of pile installation.
20. iii) Combined end bearing & Friction pile
• This type of pile foundation is mostly used in construction.
The advantage of using this pile is that it can resist loads from
structures through both end bearing and friction resistance.
This pile has high pile capacity and is economical.
• This pile is used when the soil exploration results shows hard
bedrock or fairly compacted soils at reasonable depth and soil
above bed rock supports skin friction resistance.
• In this case,
• QU = QS + QP
• Where QU is the ultimate load capacity of pile foundation
• QS is the load carried by the friction pile or pile group
• QP is the load carried by the end bearing pile or pile group.
• The load is transferred to the soil through friction in case of
sandy soil and adhesion in case of clayey soil.
22. 3) Classification based on method of installation
i)Driven pile
• Driven pile foundations can be made from concrete, steel or timber.
These piles are prefabricated before placing at the construction site.
When driven piles are made of concrete, they are precast. These piles
are driven using a pile hammer.
• When these piles are driven into the granular soils, they displace the
equal volume of soil. This helps in compaction of soil around the
sides of piles and results in the densification of soil. The piles which
compact the soil adjacent to it is also called as compaction pile. This
compaction of soil increases its bearing capacity.
• Saturated silty soils and cohesive soils have poor drainage capability.
Thus these soils are not compacted when driven piles are drilled
through it. The water have to be drained for the soil to be
compacted. Thus stresses are developed adjacent to the piles have to
be borne by pore water only. This results in increase in pore water
pressure and decrease in bearing capacity of the soil.
23. ii) Driven & caste-in situ pile piles
• Driven and cast-in-situ piles have the advantages of both
driven and cast-in-situ piles. The procedure of installing a
driven and cast-in-situ pile is as follows:
• A steel shell of diameter of pile is driven into the ground
with the aid of a mandrel inserted into the shell. After
driving the shell, the mandrel is removed and concrete is
poured in the shell.
• The shell is made of corrugated and reinforced thin sheet
steel (mono-tube piles) or pipes (Armco welded pipes or
common seamless pipes). The piles of this type are called a
shell type piles.
24. • The shell-less type is formed by withdrawing the shell while
the concrete is being placed. In both the types of piles the
bottom of the shell is closed with a conical tip which can be
separated from the shell. By driving the concrete out of the
shell an enlarged bulb may be formed in both the types of
piles. Franki piles are of this type. In some cases the shell
will be left in place and the tube is concreted. This type of
pile is very much used in piling over water.
26. • iv) Screw pile:- These piles are screwed into the soil.
• v) Jacked piles:- These piles are jacked into the soil by
applying a downward force with the help of a hydraulic jack.
27. 4)Classification based on use
i) Load bearing pile:- These piles are used to transfer the load
of the structure to a suitable stratum by end bearing , by
friction or by both.
ii) Compaction pile :-These 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.
28. 4)Classification based on use
i) Tension pile :- These piles are in tension. These piles are used
to anchor down structure subjected to hydraulic uplift force
or overturning forces.
ii) Sheet pile:- Sheet piles form a continuous wall or bulkhead
which is used for retaining earth or water .
iii) Fender pile :- Fender pile are sheet pile which are used to
protect water front structure from impact of ships and vessel.
iv) Anchor pile :-
32. 4)Classification based on use
i) Batter pile:- When piles are driven at inclination to resist
large horizontal or inclined forces,, the piles are termed as
batter piles
ii) Fender Pile : When the piles are used to protect concrete deck
or other water front structures from the abrasion or impact
that may be caused from the ships or barges (when they are
tied up at the deck) they are called fender piles. The fender
piles are ordinarily made up of timber..
