pile installation methods_bhushan

7/28/2019 Pile Installation Methods_Bhushan

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Methods of Construction of

Pile Foundations


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Outline of Presentation

1. Methods of installation of piles

a. Driven Piles

b. Bored Piles2. Case study:- Piling work at

Bandra - Worli sea link ( BWSL )

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Methods of installation

The methods of installation of piles are mainly

divided into two types

1. Pile Driving:- In this method the pile (Precast

or cast in situ) is driven into ground by meansof automated pile driving machines.

2. Pile Boring:- In this method the pile (Mostly

Precast) is bored into ground by means of by

hand operated or automated augers.

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a. Driven Piles

The piles types which are installed using pile

driving methods includes:-

Timber piles

Steel piles Precast concrete piles

Prestressed concrete piles

Cast-in-situ piles

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a. Driven Piles

Driven piles are installed by means of a driving

hammer or a vibratory driver. The various types

hammer types includes:-

1. Drop hammer,

2. Steam or air hammer,

3. Diesel hammer

4. Hydraulic hammer.

Use of these hammer types are classified as

percussive piling, which is subject to the requirementsof Noise Control Ordinance (HKSARG, 1997).

The use of noisy diesel, pneumatic and steam

hammers for percussive piling is generally banned in

built-up areas surrounded by noise sensitive receivers4/19/2013 5


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a. Driven Piles

Driven Piles consists of assembly

1. Dolly,

2. helmet

3. packing or pile cushion

The purpose of the assembly is tocushion the pile from the hammer

blows and distribute dynamic stresses

evenly without allowing excessive

lateral movements during driving.

In addition, the life of the hammerwould be prolonged by reducing the

impact stress. Pile cushion

(or packing) is generally not

necessary for driving steel piles4/19/2013

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Drop hammers

A drop hammer (8 to 16 tonnes) is liftedon a rope by a winch and allowed to fall

by releasing the clutch on the drum.

The stroke is generally limited to about

1.2 m except for the case of 'hard

driving' into marble bedrock where

drops up to 3 m have been used inHong Kong.

The maximum permissible drop should

be related to the type of pile material.

The drawback to the use of this type of

hammer is the slow blow rate, thedifficulty in effectively controlling the

drop height, the relatively large

influence of the skill of the operator on

energy transfer, and the limit on the

weight that can be used from safety

considerations.4/19/2013 7


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Steam hammers

Steam or compressed airhammers are classified as

single-acting

double-acting

depending on whether the

hammer falls under gravity or is

being pushed down by a second

injection of propellant.

A chiselling action is produced

during driving as a result of thehigh blow rate. Some single-acting

steam hammers are very heavy,

with rams weighing 100 tonnes or

more.

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Steam hammers

Single acting Hammer Double acting Hammer

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Diesel Hammer

In a diesel hammer, the weightis lifted by fuel combustion. The

hammer can be either single-

acting or double-acting.

Due to the high noise level andpollutant exhaust gases

associated with diesel hammers,

the use of diesel hammers has

been phased out in populated

areas.

The ram weight of a diesel

hammer is generally less than a

drop hammer but the blow rate

is higher.4/19/2013 10


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Hydraulic hammer

A hydraulic hammer is lessnoisy and does not produce

polluting exhaust.

The ram of the hammer is

connected to a piston,

which is pushed upward anddownwards by hydraulic power.

Some complex models have

nitrogen charged accumulator

system, which stores significantenergy allowing a shortened

stroke and increased blow rate.

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Hydraulic Hammer (contd)

As such, the kinetic energy of the hammer depends not

only on the height of the stroke but also the acceleration

due to the injection of hydraulic pressure.

Most new hydraulic hammers are equipped withelectronic sensors that directly measure the velocity of

the ram and calculate the kinetic energy just before

impact.

The energy transfer ratio of hydraulic hammers ranges

between 0.8 and 0.9

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Vibratory hammers A vibratory driver consists of a static

weight together with a pair of contra-rotating eccentric weights such that the

vertical force components are additive.

The vibratory part is attached rigidly to

the pile head and the pulsating force

facilitates pile penetration under thesustained downward force.

The vibratory driver may be operated at

low frequencies, typically in the range of

20 to 40 Hz, or at high frequencies

around 100 Hz (i.e. 'resonance piledriving').

Vibratory drivers are not recommended

for precast or prestressed concrete piles

because of the high tensile stresses that

can be generated.4/19/2013 13


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b. Bored Piles

Bored piles are mostly formed by machineexcavation. Excavation of the pile bore may also

be carried out by hand-digging in the dry known

as hand-dug caissons . When constructed in water-bearing soils which

are not self-supporting, the pile bore will need to

be supported using steel casings, concrete rings

or drilling fluids such as bentonite slurry,polymer mud, etc.

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Machine Dug Bored Piles

The Machine dug piles are mainly divided

into:-

a.Mini Piles

b.Socketed H-Piles

c.Continuous Flight Augur piles

d.Large dia. Bored Piles

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Mini Piles

Mini-piles are in a range of 100 mm

to 400 mm in dia. and can be

constructed to a depth of 60 m

depth or more, but verticality

control becomes more difficult at

greater depths.

They can be used for sites with

difficult access or limited

headroom and for underpinning.

In general, they can overcome

large or numerous obstructions

in the ground.

A mini-pile usually has four 50 mm

diameter high yield steel bars and

has a load-carrying capacity of

about 1 375 kN.

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Socketed H-piles

Socketed H-piles are formed by inserting asteel H-pile section into a pre bored hole in

rock. The hole should have a diameter

adequate to accommodate the steel section

plus any necessary cover for corrosionprotection.

Cover to the pile tip is generally

unnecessary and the H-pile section can be

placed directly on the rock surface of the prebored hole. The common size of the pre

bored hole is about 550 mm. The hole is

then filled with non-shrink cement grout.4/19/2013 17


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Socketed H-piles

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Continuous flight auger piles

Sizes of CFA piles range from 300 mm to 700 mm indiameter and their lengths are generally less than 30 m.

Once concreted, reinforcement bars or a steel H-pile

section may be inserted to provide resistance to lateral

load or to increase the load-carrying capacity.

These piles can be installed with little noise and

vibration and are therefore suited for sites in urban

areas.

However, this type of piles cannot cope with boulders.

The lack of penetration under continuous rotation due toa hard layer or an obstruction can lead to soil fighting upthe auger causing ground loss and settlement.

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Large Dia. Bored piles

Large-diameter bored piles are used to supportheavy column loads of tall buildings and

highways structures such as viaducts.

Typical sizes of these piles range from 1 m to 3

m, with lengths up to about 80 m and workingloads up to about 45 000 kN ( 4.5 Lakh tonnes ).

The working load can be increased by socketing

the piles into rock or providing a bell-out (bulb) at

pile base. The pile bore is supported bytemporary steel casings or drilling fluid, such as

bentonite slurry.

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Large Dia. Bored piles

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Manual Dug Bored Piles

Hand-dug caisson is a very simple and low cost to formlarge-size bored pile due to the following reasons:

No heavy equipment is required except powered tools

Requires very little working space

Can work for a number of piles at the same time Can work at very difficult condition such as steep slope

Boulder inside the bore can be cut fairly easily by human

worker.

The only drawback is that it is very dangerous for workerworking inside the caisson. Therefore, in 1998, the use of

hand-dug caisson was banned due to the high accident rate.

However, under special condition (e.g. work in steep slope),

approval can still be obtained subject to the fulfilment of

certain safety requirements.4/19/2013 24


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Manual Dug Bored Piles

The Manual dug piles are mainly divided

into:-

a.Piles using Caisson

b.Piles using chisel and grab

c.Reverse Circulation Method

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Piles using Caisson

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Piles using chisel and grab

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Piles using Reverse Circulation Drilling

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Foundation design of Bandra-Worli

Sea Link (BWSL)

The Bandra-Worli Sea Link is primarily

meant to provide an alternative to the

Mahim causeway route that is

presently the only connection

between South Mumbai and

the Western and Central suburbs.

In the first phase it will connect

Bandra to Worli whereas in the

subsequent phases the plans

are to take it further to Haji Ali

and then to Nariman Point.

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Pile Design of BWSL

The foundations for the BWSL project consist of1. 120nos of 2.0m piles

2. 484nos of 1.5m piles

The project's site geology consists of basalts, volcanic tuffs

and breccias with some intertrappean deposits The major engineering problems that needed suitable

solutions before proceeding with the work were as follows:

Highly variable geotechnical conditions of the foundation

bed as explained above. Highly uneven foundation bed even for plan area of one pile.

Presence of Intertidal Zone (Foundation Bed exposed in

low tide and submerged in high tide).

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Problems encountered during

Pile Driving Reverse Circulation Drilling method is adopted for foundation construction. The

highly uneven foundation beds and the presence of intertidal zone brought in lots

of difficulty in terms of Liner pitching.

This problem was solved by constructing a gabion boundary at the bed level

around the casing, pouring concrete between the casings to make an artificial

penetration of the casing. After setting of the concrete under the water, drilling was

commenced using RCD.

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Pile Driving It is interesting to note that loss of water head during continuous

drilling operation was a major problem while working in the intertidal

zone. This water head loss lead to very slow production rate and

very high consumption of drill bits. To overcome this problem, pits

were made in the low tide at each foundation location using an

Excavator and the casing was placed at the bottom of the pits.

Then the casing was placed

in the pits and was concreted

to make an artificial penetration,

maintaining the proper

water head for continuous drilling.

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Pile Driving For several locations, cofferdam construction using steel liner

and sheet piles, was not possible due to very hard and

uneven strata.

Here the problem was solved using circular steel caissons.

These caissons were fabricated outside and towed to locationusing A-frame barge. The caissons were sunk at the location

using counterweights.

The unevenness at the bottom was sealed using the gabion

method. The benefit of this method was that it completely

eliminated deployment of resources like Jack up Platform,Crane, Vibro hammer, Compressor, etc. for liner pitching.

It also eliminated substantial amount of field works and is

pre-fabricated in principle.

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References

Textual Content Foundation design and construction

GEO Publication No. 1/2006, Hong Kong

Foundation analysis and design

by Joseph E. Bowles Geotechnical Engineering

by V.N.S.Murthy

Images:-

www.images.google.com

Case Study:-

Making of BWSL - www.hccindia.com

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