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PILING TECHNIQUES
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Piling is a type of Foundation which is defined as a columnsupported type of foundation, may be cast in-situ or pre-cast.
It may be made of Timber, Concrete, Steel, or combination of
any of them.
Pile foundation is adopted when the loose soil extends to a
great depth.
The load is transmitted by the piles to the hard stratum below or
it is resisted by the friction developed on the sides of piles.
Piling process involves lifting and holding the pile into position
and driving until it stops due to hard strata or reaches to a
specified depth.
PILING
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End bearing piles are those which terminate in hard, relatively
impenetrable material such as rock or very dense sand and gravel.
They derive most of their carrying capacity from the resistance of
the stratum at the toe of the pile.
END BEARING PILES
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Friction piles obtain a greater part of their carrying capacity by
skin friction or adhesion. This tends to occur when piles do notreach an impenetrable stratum but are driven for some distance
into a penetrable soil. Their carrying capacity is derived partly
from end bearing and partly from skin friction between the
embedded surface of the soil and the surrounding soil.
FRICTION PILES
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Settlement reducing piles are usually incorporated beneath the
central part of a raft foundation in order to reduce differential
settlement to an acceptable level. Such piles act to reinforce the
soil beneath the raft and help to prevent dishing of the raft in the
centre.
SETTLEMENT REDUCING PILES
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1. Displacement piles: Displacement piles cause the soil to bedisplaced radially as well as vertically as the pile shaft is
driven or jacked into the ground.
2. Non-Displacement piles:Non-displacement piles soil is
removed and the resulting hole filled with concrete or a pre-cast concrete pile is dropped into the hole and grouted in.
TYPES OF PILES
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1. Rotary Bored Piling
Compact powerful trackand lorry mounted rotary bored
pile equipment enable Foundation
Piling to provide edge of
highway, bridge abutment and
restricted access bored piling
solutions.
Advantages: Fast
Cost Effective
On-site relocation
METHODS OF PILE DRIVING
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Capabilities
Diameters: 350 - 1400 mm; depths up to 35 m. Oscillated casing, polymers or bentonite.
Alternative engineered solutions.
Applications Continuous bored pile walls.
Hard / soft secant bored pile walls.
Piling into rock or banded rock strata. Piling adjacent to roads and railways.
Installation of permanent liners and Kingpost
walls
ROTARY BORED PILING
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It is the quietest form of
piling and is suitable for forming
piles in most types of soil. The
use of these techniques in low
headroom and restricted access
has in the past been limited to a
maximum of 300 mm. Advancesin rig technology have
revolutionised our capabilities.
2. FLIGHT AUGER BORED PILES
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Capabilities
Low vibration.
Restricted access and head room.
Casing installation to 15 m and bored depth up to 30 m.
Diameters all sizes up to 600 mm
Applications
Restricted access sites noise and vibration sensitive work.
Inter-bedded sequences of clays and sands.
Water bearing cohesion less strata.
Bearing piles.
Small restricted access retaining walls
FLIGHT AUGER BORED PILES
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Using sectional temporary casing tosupport unstable ground
Employed in a wide range of ground
conditions providing an effective solution to
the problems associated with pile installation
for restricted access and limited headroom
sites where high loads are to be supported.
Most components can be manuallyhandled and very little mechanical assistance
is require to negotiate stairways and corridors
for making tripod rigs.
3. TRIPOD BORED PILING
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Capabilities
Diameters from 250 mm to 750 mm.
Depths up to 35 m
Sectional casing
Methods of installation of Piles Dropping weight
Diesel Hammer
Vibratory methods
Jacking Methods
TRIPOD BORED PILING
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The dropping weight or drop hammer is the most commonly
used method of insertion of displacement piles
A weight approximately half that of the pile is raised a
suitable distance in a guide and released to strike the pile head
When driving a hollow pile tube the weight usually acts on aplug at the top of the pile tube, thus reducing any excess
stress along the length of the tube during insertion.
Variants of the simple drop hammer are the single acting and
double acting hammers.
These are mechanically driven by steam, by compressed air
or hydraulically
4. DROPPING WEIGHT HAMMER
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In the single acting hammer the weight is raised by
compressed air (or other means) which is then released andthe weight allowed to drop. This can happen up to 60 times a
minute
The double acting hammer is the same except compressed air
is also used on the down stroke of the hammer. This type of
hammer is not always suitable for driving concrete piles
however
DROPPING WEIGHT HAMMER
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Rapid controlled explosions can be produced by the diesel
hammer.
The explosions raise a ram which is used to drive the pile into the
ground.
Although the ram is smaller than the weight used in the drop
hammer the increased frequency of the blows can make up for
this inefficiency.
This type of hammer is most suitable for driving piles throughnon-cohesive granular soils where the majority of the resistance
is from end bearing.
5. DIESEL HAMMER
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Vibratory methods can prove to be very effective in driving piles
through non cohesive granular soils. The vibration of the pile excites the soil grains adjacent to the pile
making the soil almost free flowing thus significantly reducing
friction along the pile shaft.
The vibration can be produced by electrically (/hydraulically)powered contra-rotating eccentric masses attached to the pile head
usually acting at a frequency of about 20-40 Hz. If this frequency
is increased to around 100 Hz it can set up a longitudinal
resonance in the pile and penetration rates can approach up to 20
m/min in moderately dense granular soils.
Disadvantage:
The large energy resulting from the vibrations can damage
equipment, noise and vibration propagation can also result in the
settlement of nearby buildings.
6. VIBRATORY METHOD OF PILE DRIVING
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Jacked piles are most commonly used in
underpinning existing structures. By excavating
underneath a structure short lengths of pile can beinserted and jacked into the ground using the underside
of the existing structure as a reaction.
JACKING METHODS OF INSERTION