Pilefoundation

1
Advanced Construction & Equipments
MODULE-1
Prepared By: Prof. Arpan Patel
Saffrony Institute of Technology

Indian Standards on Piles
 IS 2911 : Part 1 : Sec 1 : 1979 Driven cast in-situ concrete piles
 IS 2911 : Part 1 : Sec 2 : 1979 Bored cast-in-situ piles
 IS 2911 : Part 1 : Sec 3 : 1979 Driven precast concrete piles
 IS 2911 : Part 1 : Sec 4 : 1984 Bored precast concrete piles
 IS 2911 : Part 2 : 1980 Timber piles
 IS 2911 : Part 3 : 1980 Under reamed piles
 IS 2911 : Part 4 : 1985 Load test on piles
 IS 2911 : Part 4 : 1985 Load test on piles
 IS 5121 : 1969 Safety code for piling and other deep foundations
 IS 6426 : 1972 Specification for pile driving hammer
 IS 6427 : 1972 Glossary of Terms Relating to Pile Driving Equipment
 IS 6428 : 1972 Specification for pile frame
 IS 9716 : 1981 Guide for lateral dynamic load test on piles
 IS 14362 : 1996 Pile boring equipment - General requirements
 IS 14593 : 1998 Bored cast-in-situ piles founded on rocks - Guidelines
 IS 14893 : 2001 Non-Destructive Integrity Testing of Piles (NDT) -
Guidelines
2

 A pile is a slender structural member made of steel,
concrete, wood or composite material. A Pile is either
driven into the soil or formed in-site by excavating a hole
and filling it with concrete.
 In case, the strata of good bearing capacity is not
available near the ground, the foundation of the
structure has to be taken deep with the purpose of
attaining a bearing stratum which is suitable in all
respects.
 The most common forms of deep foundation are:
a. Pile foundation
b. Cassions or well foundation
c. Cofferdams
 Pile foundation are intended to transmit structural loads
through zones of poor soil to a depth where the soil has 3

to desire capacity to transmitted the loads. Piles are
somewhat similar to columns in that load developed at
one level are transmitted to a lower level; but pile obtain
lateral support from the soil in which they are embedded
so that there is no concern with regard to buckling and ,
it is in this respect they differ from columns. Piles are
relatively long. The piles may be driven or placed
vertically or with a batter. A pile foundation usually
consists of a number of piles, Which together support a
structure.
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 The load of the superstructure is heavy and its
distribution is uneven.
 The top soil has poor bearing capacity.
 Lateral forces are relatively prominent.
 In presence of expansive and collapsible soils at the
site.
 Foundation of Transmission towers, Offshore
structures etc.
 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.
 Canal or deep drainage lines exist near the
foundations.
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1. End bearing pile
2. Friction pile
3. Compaction pile
4. Tension pile
5. Anchor pile
6. Fender pile
7. Better pile
8. Sheet pile
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End Bearing Piles
ROCK (firm layer)
SOFT SOIL
PILES
End bearing pile rests on a relatively firm soil
(support layer). 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
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SOFT SOIL
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 and the pile.
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 They are used as bulk heads or as impervious cutoff
to reduce seepage and uplift under hydraulic
structures.
18

 They are used to resist large horizontal forces or
inclined forces.
19

 Anchor piles provide anchorage against horizontal
pull from sheet piling or other pulling forces.
21

 Fender piles are used to protect water from
structures against impact from ships or other
floating objects.
22

 When piles are driven in loose granular soil
with the aim of increasing the bearing capacity
of soil, the piles are termed as compaction piles.
These piles themselves do not carry any load.
23

 These piles anchor down the structures subjected
to uplift due to hydrostatic pressure or due to
overturning moment. It is also called uplift pile.
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 Timber Piles
 Untreated
 Treated with a preservative
 Concrete
 Precast Concrete Piles
 Cast-In-Place Concrete Piles
 Steel Piles
 H- Piles
 Sheet Piles
 Pipe Piles
 Composite Piles ~
 Concrete & Steel
 Plastic with steel pipe
core
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 Advantages:
 More popular lengths and
sizes are available on
short notice
 Economical in cost
 They are handled easily,
with little danger of
breakage
 After driving, they can be
easily cut to any desired
length
 Can be extracted easily if
needed
 Disadvantages
 May be difficult to obtain
piles sufficiently long and
straight
 Can be difficult or
impossible to use in hard
formations
 Difficult to splice
 Usually not suitable to use as
end-bearing piles – better for
friction bearing piles
 Usually require treatment
with preservatives to
maintain structural capacity
over required duration –
possible environmental
impact.
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 Advantages:
 Have high resistance to
chemical and biological
attacks
 Have high load-carrying
capacity
 Disadvantages
 Difficult to reduce or
increase the length
 Large sizes require heavy
and expensive handling
and driving equipment
 Inability to quickly obtain
piles may delay the
starting of a project
 Possible breakage of piles
during handling or
driving produces a delay
hazard
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 Probably the best for
deep depths
 Can be easily cut and
spliced.
 Most common shapes
are:
 Steel H Sections
 Steel-Pipe Piles
 Screw Piles
33

 Composite Piles are
piles of two
different materials,
driven one over the
other, so as to
enable them to act
together to perform
the function of a
single pile.
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 Advantage is taken of the good qualities of
both the materials. These prove economical as
they permit the utilization of the great
corrosion resistance property of one material
with the cheapness or strength of the other.
 Composite pile is used with the object of
achieving economy in the cost of piling work.
 Another type of composite piles commonly
used consists of a steel pipe or H-pile at the
bottom and cast-in-situ concrete pile at the top.
This type of composite pile is recommended in
cases where the designed length of the pile
works out to be greater than that available for
the cast-in-situ type of pile.
36

Based on method of
Installation
37

 Piling techniques can be split into 2 categories;
 Displacement
 Replacement.
 In simple terms, during the displacement piling
method, piles are driven into the ground pushing
the ground out of the way, as you would see in
sheet piling. Displacement piling is good for e.g.
contaminated sites where it costs a lot to take the
spoil away.
 Using the replacement piling method, muck is
dug out and replaced with the pile. We can use far
bigger piles using replacement piling.
38

 Pre cast concrete driven piles
 Thick wall driven steel tubes
 Thin wall bottom driven piles
 Timber piles
 Screw piles
 Helical displacement piles
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 The advantages of displacement piling are:-
 Self testing as driven to refusal or "set"
 No pile arisings to dispose of
 Little disturbance
 Limited access
 High production
 The disadvantages of displacement piling
are:-
 Cannot penetrate obstructions
 Cannot always penetrate dessicated clay
 Vibration and noise may be an issue
40

 Auger piles
 Large diameter rotary piles
 The advantages of replacement piling are:-
 Effectively vibration free
 Installed into non cohesive and water bearing soils
 High production
 Restricted access
 The main disadvantage of replacement piling
is that:-
 It produces excavated material which requires
removal off site.
41

Based on load carrying
characteristics
48

 Based on load carrying characterisitics or mode of
transfer of loads, the piles are classified as under
1. End bearing Piles- Before discussed
2. Friction Piles- Before discussed
3. Combined end bearing and friction Piles
 These Piles transfer the load by a combination of end
bearing at the bottom of the pile and friction along
the surface of the pile Shaft. The load carrying
capacity of the pile in this case depends on the
bearing capacity of the stratum soil below and the
skin friction along the surface of the pile.
 Total load carried=Pile point + Skin friction
1. Qn=Qp + Qs
49

 In case of Wooden Piles, Steel piles, Pre-cast concrete piles
to protect the top and bottom of the pile while driving
into the ground and to facilitate easy pile driving certain
accessories are required such as;
1) Pile Cap
 In case of driven pile, piles are driven in to the ground by
applying blows of a heavy hammer on their tops. Thus, to
protect the top of pile, pile cap is provided. Normally, pile
cap is made of steel. The thickness and size of pile cap
depends upon the shape and size of the pile driving
hammer. The pile should penetrate into the cap for atleast
10 cm length.
 In case of group of piles, a common cap of R.C.C. is
provided for all the piles. This cap carrying the load from
the structure and distribute it to various piles.
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2) Pile Shoe
• While driving wooden or steel pile by hammer the bottom
end of the pile gets damaged causing difficulty in driving.
Therefore a pile shoe is fitted at the bottom end of the pile
to protect the pile and to facilitate easy pile driving. Pile
shoes are made of cast iron, steel or wrought iron.
52

 Drop
 Steam or compressed air
 Diesel
 Hydraulic
 Vibratory
56
Pile Hammers

 Advantages
 Small investment in
equipment
 Simplicity of
operation
 Ability to vary
energy per blow by
varying the height
of fall
 Disadvantages
 Slow rate of driving
piles
 Danger of damaging
piles by lifting hammer
too high
 Danger of damaging
adjacent buildings as a
result of the heavy
vibration caused by a
hammer
 Unable to use directly
for underwater driving
58

 Uses a freely falling
weight that is lifted by
steam or compressed air
 Length of the stroke
and energy per blow
may be decreased by
reducing the steam or
air pressure
59

 Advantages
 Greater # of blows per
minute permits faster
driving
 Reduction in the
velocity of the ram
decreases the danger of
damage to piles during
driving
 Enclosed types may be
used for underwater
driving
 Disadvantages
 Require more investment
in equipment
 They are more
complicated, with higher
maintenance cost
 Require more time to set
up and take down
 Require a large crew to
operate equipment
 Require a crane with a
greater lifting capacity
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 Advantages
 Requires no external source
of energy – more mobile
 Economical to operate – fuel
consumption is less
 Convenient for remote areas
– not necessary to provide a
boiler, water for steam.
 Operates well in cold areas
 Hammer is light in weight
compared to a steam hammer
of equal rating
 Energy per blow increases as
driving resistance increases
 Disadvantages
 Difficult to determine the
energy per blow since it
depends on driving
resistance
 May not operate well in soft
ground conditions – pile has
to offer sufficient driving
resistance to activate the ram
 Number of strokes per
minute is typically less than
for a steam hammer
 Length of a diesel hammer is
slightly greater that the
length of a steam hammer
62

 Especially effective when
piles are driven into
water-saturated
noncohesive soils
 May be problematic to
use to drive piles into dry
sand or into cohesive soils
that do not respond to the
vibrations.
64

 For end bearing and skin friction to develop the
pile must move downwards in relation to the soil.
 There are, however, occasions when after a pile
has been installed, the soil surrounding the pile
begins to move downwards in relation to the pile.
When this occurs, the soil exerts a downward
drag on the pile. This downward drag is called
negative skin friction.
 Consider a soil profile underlain by a hard
stratum.
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 The magnitude of the negative skin friction, Qnf is
computed as under,
 For cohesive soil:
Qnf= P. C. Lf
Where,
Qnf =Negative skin friction
P=Perimeter of pile
C=Cohesion of soil
Lf =Length of loose fill
 For Cohesionless Soil:
Qnf= ½ P. Lf2. γ. K. tanδ
Where,
P=Perimeter of pile
K=Coefficient of earth pressure
Lf =Length of loose fill
δ=Angle of wall friction
67

 It is necessary to subtract the negative skin
friction force from the ultimate bearing load to
obtain the net ultimate load carrying capacity of
the pile (Qu’)
Qu’= Qu- Qnf
Where,
Qu’=Net ultimate load
Qu=Ultimate bearing load
• Where it is anticipated that negative skin friction would impose
undesirable, large downward drag on a pile, it can be eliminated by
providing a protective sleeve or a coating for a section which is
surrounded by settling soil.
68

 In the case of static cone penetration test, a 60o cone with a
base 100 mm2 attached to one end of a rod housed in a
pipe and the pipe itself are pushed down alternatively at a
slow constant rate and the resistance encountered by cone
and the sleeve(pipe) are recorded by means of pressure
gauges. The pressure offered by the cone is recorded as
static cone penetration resistance qc, and that offered by
the pipe as static skin friction resistance fc.
 Meyerhof (1965) relates the unit point resistance(qp) and
the unit skin friction (fs) of driven piles to the cone
resistance (qc).
 Point resistance,
qp= qc/10 x (Db/B)
69

 Unit skin friction,
a) fs= qc/200 ….. For dense sand
b) fs= qc/400 ….. For loose sand
c) fs= qc/150 ….. For silt
70

 The pile load test is the most reliable method of
determining the load carrying capacity of a pile. This test
can be performed either on a working pile which form the
structure or on a test pile.
71

 The set-up for the load test on a pile consists of two
anchor piles provided with an anchor girder or a
reaction girder at their top as shown in fig. The test
pile is installed between the anchor piles in the
manner in which the foundation piles are to be
installed. The test pit should be at least 3D or 2m clear
from the anchor piles.
 The load is applied through a hydraulic jack resting
on the reaction girder. The measurements of a
settelement of the pile are recorded with the help of
three dial gauges with respect to a fixed reference
mark. The test is conducted after period of 3 days
after installation of the test pile in sandy soils, and
after a period of one month after the installation of the
test pile in silt and soft clay. This is because by driving
the test pile the soil properties are restored.
 The load is applied in equal increment of about 20%
of the allowable load. Settlement should be recorded
with three
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Dial gauges. Each load increment is maintained till the rate
of movement of the pile is not more than 0.1 mm per hour
in sandy soils and 0.02 mm per hour in clayey soils or a
maximum of two hours(IS: 2911-1979).
• For each load increment settlements are observed at 0.5, 1,
2, 4, 8, 12, 16, 20, 60 minutes. The loading should be
continued up to twice the safe load or the load at which the
total settlement reaches a specified value. The load is
removed in the same decrements at 1 hour interval and the
final rebound is recorded after 24 hours after the entire load
has been removed.
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