CONSTRUCTION
TECHNOLOGY
CEM 571
PILing
LEARNING OUTCOME
At the end of lecture, student will be able to :
Explain various types, functions and
factors of selections for piling. (CO1; PO2)
Introduction
Function: To transmit foundation loads through soil
strata of low bearing capacity to deeper
soil or rock strata having a high bearing
capacity, or used in normal ground
condition to resist heavy uplift forces or in
poor soil conditions to resist horizontal
loads.
Piles can generally be classify with respect to their
function :- Friction piles or End Bearing Piles.
FRICTION PILES
In cohesionless soils the applied load is
transferred to the surrounding soil mainly
through skin friction along the surface of
the piles. A large part of load is also
carried by the pile toe. The skin friction
resistance varies mainly with relative
density of the soil and with the shape of
the pile.
Friction piles in cohesive soil almost the
whole load on the pile is transferred to the
surrounding soil along the pile surface
through skin friction and only a very small
part through the pile toe.
END BEARING PILES pilesdriven down to a layer with
high bearing capacity, the applied load is transferred from
the pile to the surrounding soil mainly through the pile toe
Classification of Piles
Displacement Piles
Piles are driven or
pushed, vibrated or
screwed into the
ground, displacing
the soil outwards
and downwards but
no materials are
removed.
Replacement Piles
A hole is form in the
ground by removal
of material from the
ground and thus
material is displaced
by a concrete
material formed in
the ground.
DISPLACEMENT PILES
DRIVEN PILES Preformed unit driven
into the soil by blows of hammer.
Materials of performed pile are :Timber ;
Concrete; or
Steel
Advantage of performed unit can be inspected and
checked as a sound structural member before it is driven into
the ground
Length of pile to be driven depends on the local variation of
soil strata. Disadvantages when cutting off unwanted pile or
the addition of extra lengths can become an expensive
additional cost.
Driven -Timber Piles
Usually square sawn timber of sizes 225 x
225 to 600 x 600mm.
Easy to handle and driven by percussion
or drop hammer.
Most timber piles are fitted with an iron or
steel driving shoe to prevent splitting due
to driving, and have iron ring around the
head to restrict brooming of the pile head
due to overdriving.
Timber pile is not suitable of driving
through dense strata or strata with
obstruction.
cont..
Driven -Timber Piles
Characteristic of Timber Piles :1. Must be free from short or reverse
bends, large or loose knots, slake, splits
and decay.
2. Must be free from short or reverse bends
and from crooks > 11/2 diameter of the
pile at the middle of the bend.
3. Straightness of grain line between
centres of butt and tip must be within the
body of the pile.
4. Uniform taper from the butt to tip.
Driven Precast Concrete Piles
Used where soft soils overlaying a firm
strata are encountered. Lengths up to 18m
with section sizes ranging from 250 x
250mm to 450 x 450mm carrying loadings
up to 1000kN.
The precast concrete driven pile has little
frictional bearing strength since the driving
operation moulds the cohesive soils
around the shaft which reduces the
positive frictional resistance.
cont..
Driven Precast Concrete Piles
Available Precast Concrete Piles are :Precast Reinforced Concrete Piles made of
concrete statically cast in uniform section before
driving into ground and reinforced with steel bars.
Precast Pretensioned Concrete Piles - made of
concrete statically cast in uniform section & suitably
reinforced with pretensioned prestressing steel.
Precast Pretensioned Spun Concrete Piles hollow
pile made of concrete cast by centrifugal spinning.
Suitably reinforced with pretensioned prestressing
steel.
cont..
Driven Precast Concrete Piles
Problem encounter when using this pile in
urban area : Transporting the complete length of pile
through narrow or congested streets;
The driving process which is generally
percussion can set up unacceptable noise
or vibration;
Many urban sites are themselves
restricted or congested thus making it
difficult to manoeuvre the long piles length
around the site.
Driven Steel Piles
Two main types of steel pile in general use:-
H-section pile usually in the form of wide flange
sections. It do not cause large displacement of the
soil, thus useful where upheaval of the surrounding
ground would damage adjoining property or where
deep penetration is required through loose or
medium dense sands.
Disadvantage is the tendency to bend on the weak
axis during driving. Results in considerable curvature
if driven in deep penetration. Also has low resistance
to penetration in loose sandy soil.
cont..
Driven Steel Piles
Box Piles steel box piles are fabricated
by welding together steel plates or trough
section to form hollow piles capable of
carrying very high compressive uplift or
lateral loads.
DRIVEN and CAST IN- PLACE PILES
Displacement pile formed by driving a tube with
a closed end either with a plug or loose shoe into
the soil to the required depth or set. A
reinforcement and concrete is filled in the tube.
This tube may or may not be withdrawn.
Suitable where the length of pile required varies.
Economically formed in diameter of 300 to 600
mm and can carry loads of up to 1300kN.
Required heavy piling rig, open level site and
site where noise is restricted.
cont..
DRIVEN and CAST IN- PLACE PILES
Franki driven in-situ piles
BORED and CAST IN- PLACE PILES
Is a replacement pile . Pile formed by boring a hole
in the soil, thus removing a column of soil and
replace it with in-situ concrete.
Suitable to use in sites where piling work to be
carried out close proximity to existing building or
where vibration or noise restricted.
It is carried out by dropping a heavy cutter to dig into
the ground and then raising and remove the spoil
material which it brings with it.
Formation of holes can be by :percussion bored, or
rotary bored.
ADVANTAGES
Length can be readily varied to suit varying ground
condition.
Soil remover in boring can be inspection and if
necessary sampled or in situ test made.
Can be installed in vary large diameter.
End enlargement up to two or three diameters are
possible in clay.
Material of piles is not dependent on handing or
driving conditions.
Can be installed in vary long length.
Can be installed without appreciable noise or
vibration.
Can be installed in condition of very low head room.
No risk of ground heave.
DISADVANTAGES
Susceptible to waisting or necking in squeezing
ground.
Concrete is not places under ideal condition and
cannot be subsequently inspection.
water under artesian pressure may pipe up pile shaft
washing out cement.
Enlarge and cannot be formed in cohesionless
material.
cannot be readily extended above ground level
especially in river and marine structures.
Boring method may loosen sandy and gravelly soils.
Sinking piles may cause loose of ground in
cohesionless soil, leading to settlement of adjacent
structures.
cont..
DRIVEN and CAST IN- PLACE PILES
Problems normally encountered :1. Necking due to ground water movements
washing away some of the concrete thus
reducing the effective diameter of the pile shaft
and consequently the cover of concrete over
the reinforcement.
2. Ground heave caused by displacement of
the soil by the drive tube. Can cause tension
failure in the shafts of adjacent piles already
driven and in worst case lifting of the
completed piles. However, this can be
minimized by the enlarged base of the piles in
conjunction with reinforcement in the shaft thus
anchoring the piles against uplift.
cont..
Percussion Bored Piles
Suitable for clay and / or gravel subsoil.
Diameter from 300 to 950 mm and designed to
carry load up to 1500 kN.
cont..
Percussion Bored Piles
Steel tube of length 1 to 1.4m screwed together is
sunk by extracting the soil from within the tube liner
using percussion cutters.The tube liner normally sink
under its own weight but can also be driven in with
slight pressure using hydraulic jack.
When correct depth achieved, a cage of reinforcement
is placed within the liner and then filled it with concrete.
Tamping is carried out as the liner is extracted by
using a winch or hydraulic jack operating against a
clamping collar fixed to the top of the steel tube lining.
An internal drop hammer can also be used to tamp
and consolidate concrete but usually compressed air is
used.
cont..
Rotary Bored Piles
Suitable for most cohesive soil e.g. clay.
Formed using an auger which may be operated in
conjunction with the steel tube liner.
This auger is normally mounted on a lorry or tractor,
raised to the surface and spun off the helix to the side of
the bore hole where the spoil is removed. If flight auger is
used,the spiral motion will brings the spoil to the surface.
Grab Construction - Cased
Using crawler crane and casing oscillator
Main soil sand and gravels with high demands on casing technology
Used chisels to break up bedrock and boulders
Pile diameter ranging from 620-2000mm
Depths generally up to 50m
Rotary Drilling with kelly -Cased
Standard cast-in-place pile :Use in all types of soil
Use where site conditions are restricted
Vibration free drilling. Casing installed by rotary drive
Casing oscillator can be used for larger pile diameters and greater depths.
Pile diameter generally 600 1800 mm
Depth generally up to 40 m but greater depth possible.
Rotary Drilling with kelly Borehole
supported by hydrostatic pressure
1. Rotate or vibrate
starter casing to
required depth.
2. Remove driilling spoil
with bucket attached
to kelly bar with
borehole supported
by slurry.
3. Recycle slurry to
remove soil and
insert reinforcing
cage.
4. Place concrete
simultaneously
displacing slurry.
5. Complete pile
Rotary drilling using twin rotary head
Front of Wall
Suitable for all types of soil and on restricted sites.
Vibration free, and can be installed against existing wall. Continuous flight
auger and casing installed simultaneously by counter rotating twin rotary
drives. Pile diameter from 305 to 550mm and depth generally up to 15m
1. Install casing and
continuous flight auger
to require depth using
counter rotating drives.
2. Inject concrete through
hollow stem auger,
simultaneously
withdrawing auger and
casing.
3. Insert reinforcement
cage into concreted
borehole.
4. Completed pile
Rotary drilling using flight auger
Continuous flight auger system
All types of soil and at restricted sites.
Vibration free. Reinforcement can be pushed or vibrated into fresh the fresh
concrete. Diameter from 400 1000mm . Depth generally up to 18 m.
1. Rotate continuous
flight auger to required
depth.
2. Inject concrete
through hollow stem,
simultaneously
withdrawing auger
without rotation.
3. Vibrate or push
reinforcement cage
fitted with spacers into
fresh concrete.
4. Completed pile.
COMPOSITE PILES
Combination or two or more types as
mentioned or combination of different
materials in the same types of pile.
Used in ground conditions where
conventional piles are unsuitable or
uneconomical.
Examples of composite piles :Prestcore pile
Shell pile
Cased pile
COMPOSITE PILES :Prestcore pile formed inside a line bored hole. It
is a replacement pile and can be of precast or
insitu concrete.
Advantage Problem of necking is eliminated
which made it suitable to use in waterlogged
soils.
Construction stage :1. Lined bored hole formed by percussion bored
method.
2. Precast units which form the core of the pile
are assembled on a special mandrel and
reinforcement is inserted before the core unit is
lowered into position.
3. By means of pneumatic winch, the raising and
lowering the pile core which is attached to the
head of lining tube to consolidate the bearing
stratum.
4. Withdraw the lining tube and grouting with the
aid of compressed air to expel any ground
water.
COMPOSITE PILES :-
Shell
Is a driven or displacement pile consisting of a series of precast
shells threaded on to a mandrel and top driven to the
required set.
After driving and removing the mandrel the hollow core can be
inspected, cage of reinforced can be inserted and void filled
with in-situ concrete.
Suitable in waterlogged and soft substrata with readily
adaptable length.
Advantages :1. The shaft can be inspected internally
before in-situ concrete is introduced,
2. the flow of water or soil into the pile is
eliminated,
3. The presence of corrosive conditions in
thes soil can be overcome using special
cements in the shell construction.
COMPOSITE PILES :Cased Pile
Using steel strip or plate which
is formed into a continuous
helix with
adjoining edge butts welded
as driving tube and filled
with in-situ concrete.
Driven into position by
internal drop hammer
operating within the casing.
Factor governing the selection of piles :-
1.
Location and type of structure driven or driven and cast
in-place pile where shell remains in position are most favour
for works over water.
Structures on land provide wide choice of types usually
chosen the cheapest for moderate loading and unhampered
site condition.
If proximity of existing structure should choose the types
without giving ground heave, vibration or noise.
Factor governing the selection of piles :1.
Ground condition influence the pile types and
techniques.
E.g. driven piles not economical to use in ground
condition containing boulders and where ground heave
would be detrimental.
Driven piles preferred for loose water bearing sands or
gravels where compaction due to driving can develop the
full potential bearing capacity of these soils.
Steel H-pile gives low ground displacement suitable
where deep penetration require in sand and gravel.
Stiff clay favour for bored and under-reamed types.
Factor governing the selection of piles :-
Durability in marine condition suitable to
use precast concrete pile, while timber is
rejected in such condition
Type of pile shoe for various ground condition
PILE TESTING
Objective is to confirm that the
design and information of the
chosen pile type is adequate.
Test piles are usually overloaded
by at least 50% of the design
working load to near failure or to
actual failure.
Record of driving
resistance of test pile
LOAD TEST
