Pile foundations_Advanced Construction Technology

Prepared By
Prof. Ashish Makwana
Civil Engg. Dept.
Prof. Ashish Makwana 1

PRESENTATION
OUTLINE…
• Introduction
• Uses of Piles
• Factors affecting selection of type of piles
• Types of Piles
• Pile Spacing
• Group of Piles
• Efficiency of Group of Piles
• Pile Cap and Pile shoe

PRESENTATION
OUTLINE…
• Load tests on piles
• Pile driving
• Pulling of piles
• Loads on piles
• Causes of failure of piles
• Pile driving formulas

INTRODUCTION
• When the depth of foundation is more than the
width of foundation then it is termed as deep
foundations.
• The deep foundations are classified as below :
– Pile foundations
– Cofferdams
– Caissons

Pile foundation
CaissonCofferdam Prof. Ashish Makwana 5

Pile foundation

PILE FOUNDATION
• Pile foundation is that type of deep foundation in
which the loads are taken to a low level by means of
vertical members which may be of timber, concrete
or steel.

Pile applications
Soft to
Firm Clay
Large Distributed
Weight
Very Large Concentrated
Weight
Strong Rock
Low
Weight

USES OF PILES
• (i) Pile foundation is generally used, when simple
spread foundation at a suitable depth is not possible
either because the stratum of required bearing
capacity is at a greater depth or steep slopes are
encountered.
• (ii) In compressible soil or water-logged soil or soil of
made-up type, piles are used with advantage for
providing safe foundation for any type of structure.
• (iii) Piles are used for foundation for buildings,
trestles, bridges and water front installations (piers,
docks, etc.) Prof. Ashish Makwana 9

• (iv) The load coming from the structure is very heavy
and the distribution of load on soil is uneven.
• (v) They are also used in normal ground conditions
to resist heavy uplift forces or in poor soil conditions
to resist horizontal loads.
• (vi) The pumping of subsoil water is too costly for
keeping the foundation trench in dry condition.
• (vii) The timbering of excavations is too difficult to
maintain the sides of foundation trench.

FACTORS AFFECTING SELECTION OF
TYPE OF PILES
Location & type of
structures
Ground conditions
Durability Cost consideration

Factors affecting pile capacity
(cont’d)
 Surrounding soil
 Installation technique (like driven or bored).
 Method of construction (like pre cast or cast in
situ)
 Location of pile in a group
 Spacing of piles in a group
 Symmetry of the group
 Shape of pile cap
 Location of pile cap (like above soil or below soil)
 Drainage condition in soil

Classification of piles based on
function
End bearing pile Friction pile Compaction pile
Tension /
uplift pile
Anchor pile
Fender pile /
Dolphin
Sheet pile Better pile

Hard incompressible stratum
End Bearing Piles
G.L G.L.Pile
Friction Piles

TYPES OF PILES
Non-load bearing
piles
Bearing Piles
Pbase
Side Friction
End Bearing
Pile Load, P

1. LOAD BEARING PILES

LOAD BEARING PILES
• The load bearing piles bear the load coming from
structure above. The load bearing piles may resist
the load by directly resting on the firm stratum or by
friction developed at their sides.
• The frictional resistance can be increased by taking
various measures, such as :
– (i) By increasing the diameter of the pile.
– (ii) By driving the pile to a greater depth.
– (iii) By making surface of the pile rough.
– (iv) By placing the piles closely.
– (v) By grouping the piles.

Materials used in construction of
load bearing piles
SteelTimber
ConcreteTimber Steel H Composite
Pre-cast
Concrete
Concrete
1. Cast-iron piles 4. Steel piles
2. Cement-concrete piles 5. Timber piles
3. Sand piles 6. Wrought-iron piles
Steel Pipe

1. Cast-iron piles
• cast-iron piles: hollow
• Inside diameter of pile: 30 cm
• Thickness: 25 mm
• length of pile: 3 to 4 meters
• cast-iron: brittle, not possible to drive the piles into
the ground by means of a hammer

2. Cement concrete piles :
• RCC piles are of two types :
– 1. Cast-in-situ:
• 1.1 Driven piles:
– 1.1 (a) Cased cast-in-situ concrete piles
– 1.1 (b) Uncased cast-in-situ concrete piles
• 1.2 Bored piles:
– 1.2 (a) Pressure piles,
– 1.2 (b) Under-reamed piles,
– 1.2 (c) bored compaction piles
– 2. Pre-cast concrete piles

1.1 (a) Cased Cast-in-situ concrete piles:
– Raymond piles
– Mc-Arthur cased pile
– Union metal Monotube pile
– Sewage piles
– Western button bottom pile
1.1 Driven Piles
1. CAST-IN-SITU CONCRETE PILES

Raymond piles
Mac-Arthur piles
• used primarily as friction
piles
• length of piles: 6 to 12 m
• diameter of piles: 40 to 60
cm. at the top & 20 to 30
cm. at the bottom
• Diameter: uniform
• Pile: uses an additional
steel casing of heavy
gauge
2 types:
- Raymond standard concrete pile
- Raymond step-taper concrete pile

Monotube Piles
• Consists of tapered fluted steel shell without mandrel.
• Pile shells are driven to the required depth.
• Then interior of the shell is inspected.
• The shell is then filled with concrete.
• These piles are suitable for a wide variety of soil conditions
ranging from end-bearing to friction-load-carrying soils.

Sewage piles
Button-bottom piles
• 1st: Thin steel shell is placed on a
precast concrete plug with steel core.
• 2nd: Steel pipe is driven over the plug.
• 3rd: Steel pipe is driven to a specified
depth.
• 4th: Steel shell has reached the desired
depth and then core is removed.
• Final: Steel pipe is filled with concrete.
conical shape
• 1st: Set up the steel pipe.
• 2nd: Steel pipe and button is driven
upto the required depth.
• 3rd: Corrugated steel shell is inserted
inside the steel pipe.
• Final: The steel pipe is withdrawn,
leaving the button (25 mm
diameter) in place and shell is filled
with concrete.
• Pile length: 23m, and load carrying capacity upto 50 tonnes

1.1 (b) Uncased cast-in-situ concrete piles:
• These piles are comparatively cheap, as no casing will
be left in the ground. But, great skill is required in
this case to achieve the desired results.
• The common types of uncased cast-in-situ concrete
piles are :
(i) Simplex piles (ii) Franki piles
(iii) Vibro piles (iv) Pedestal piles

Simplex piles
• A steel tube is fitted with cast-iron shoe.
• Reinforcement is placed in the tube.
• Tube is slowly withdrawn after filling concrete.
cast-iron shoe

Franki piles
• The pile has an enlarged base of mush-room shape, which
give the effect of a spread footing.
20 to
30 kN
• Franki pile diameter
is 50 to 60 cm while
enlarged base
diameter is 90 cm
• The pile has a
carrying capacity of
60 to 90 tonnes.

Standard Vibro piles
Vibro-expanded piles
• Vibro piles is formed
by driving a steel tube
and a cast-iron shoe,
filling with concrete.
• Extracting the tube
using upward
extracting and
downward tamping
blows alternatively.
• Vibro-expanded piles: the
bearing capacity of soil is
increase by enlarging its
diameter at the bottom
• Dia. 35, 45, 50 cm
• Load 60 to 70 tonnes
• Length 25 m
cast-iron
shoe

• In the first stage of
this pile, a casing tube
with a core is driven
upto required depth.
• In the second stage,
the core is withdrawn
and a layer of concrete
is deposited in the
casing.
• In the third stage, the
core is placed again in
the tube. The pressure
is applied on the
concrete through the
core and at the same
time, the casing is
withdrawn.
Pedestal piles
1st stage 2nd stage 3rd stage

1.2 Bored Piles
• Bored piles are those which are formed by forming a
bore hole in the ground and then concreting it, either with
the help of a casing tube or without a casing tube.
• Their procedure of construction is thus different than the
cast-in-situ driven pile where a heavy pile driving
equipment is required.
• These piles have advantage over the driven piles, in
those locations and those situations where the vibrations
and noise caused by driving of piles are to be avoided or
the strata of adequate bearing capacity is so deep that
they are difficult to reach by driven piles.

1.2 (a) PRESSURE PILES
1.2 Bored Piles
Pressure Piles
• Steel casing 1.2 to 1.8 m
long, 400 mm dia.

• They are formed with the help of a casing tube, boring
auger and compressed air equipment.
• These piles are especially suitable for those congested
sites where heavy vibrations and noise are not
permissible, and also where heavy pile driving
machinery can not move in.
Procedure:
• 1. Steel casing is sunk in the ground, while a boring tool,
such as an auger, working inside it, excavates the soil.
• 2.Further section of steel casing are screwed
successively and sunk in the ground.

• 3. A charge of concrete is placed in the tube, and the
upper end of the tube is closed with the help of pressure
cap. Compressed air is introduced through the air pipe of
the pressure cap, thus forcing the concrete down and out
against the surrounding soil. Simultaneously, the tube is
slowly extracted with the help of a winch.
• 4. Fresh charges of concrete are placed in the tube,
before the end of the tube comes above the previous
charge of concrete, and the process of compressed air
application is repeated, till the complete pile is cast and
tube is completely taken out.
• If it is required to increase the bearing value of the pile,
an enlarged base is formed by introducing cement grout
after the tube is sunk, and forcing is by air pressure into
the adjacent soil.

• The under-reamed piles are provide an ideal solution
to foundations in black cotton soil.
• Diameter of an under-reamed piles: 20 cm. to 50 cm
• Diameter of the bulb 2 to 3 times the diameter of
pile.
• Under-reamed piles: reinforced with 10 to 12 mm.
dia. longitudinal bars and 6 mm. dia. of rings.
• A clear cover of 4 cm. is provided.
• The under-reamed piles are connected by a
reinforced concrete beam, known as capping beam.
1.2 (b) UNDER-REAMED PILES

Under-reamed pile foundationProf. Ashish Makwana 35

Under-rammer with
Bucket
Auger boring

1.2 (c) BORED COMPACTION PILES
1.2 (c) BORED COMPACTION PILES

• Modification of under-reamed piles
• One type of cast-in-situ pile which combine the
advantages of both bored and driven pile
• Method of boring the piles and concreting the pile is
same as that for under-reamed pile, except that the
reinforcement cage is not placed in the bore hole before
concreting. After the concreting is over, the
reinforcement cage is driven through the freshly laid
concrete.
• Due to this feature, the compaction of surrounding soil
as well as concrete are effected and the load-carrying
capacity is increased by 1.5 to 2 times over normal
under-reamed piles.
• These piles are particularly suitable in loose to medium
dense sandy and silty strata.
BORED COMPACTION PILES

Procedure:
• Prepare the bore hole with the help of spiral auger, using
guides, and then under-ream it with the help of under-reaming
tool. Concrete the pile, without placing the reinforcement
cage.
• Place of reinforcement cage, enclosing a hollow driving pipe,
on the top of freshly laid concrete. A cast iron conical shoe,
with a iron cleat welded to it, attached to the reinforcing cage.
• Drive the driving assembly through the freshly laid concrete to
the full depth by means of suitable drop weight (about 5kN),
operated with the help of mechanical winches. As the cage is
driven into the concrete, soil and concrete gets compacted.
This would result in increase in the diameter of the bore hole.
Extra concrete is simultaneously poured to keep it level with
the ground.
• After driving through the full depth of concrete, fill concrete in
the hollow drive pipe also. The pipe is then gradually
withdrawn leaving the cage and concrete behind.Prof. Ashish Makwana 39

Precast Concrete Piles
• Pre-cast pile: moulded in circular,
square, rectangular or octagonal
form
• Piles: cast and cured in casting
yard and then transported to the
site for driving
• size of the pile:
- diameter 30 to 50 cm.
- length may be 4.5 m. to 30 m.
• Steel bars: 20 to 40 mm
• 4 to 8 nos. with lateral ties of 5 to 10
mm wire spaced at 10 cm c/c for top
and Bottom 1 m length and 30 cm c/c
for middle length, concrete cover 50
mm
2. PRECAST CONCRETE PILES

3. Sand Piles
• Sand piles is spaced at 2 to 3
metres, usually under the
columns of the structure.
• A properly constructed sand pile
can take up a load of 100 tonnes
per sqmt. or more.
• Dimensions of sand pile is
determined from the load
coming upon it.
• Length: 12 times its diameter
Sand Piles

4. Steel Piles
H-beam Piles
Box Piles
Tube Piles
• H-beam piles: wide flange section
• Most common variety of steel piles in
general use
• Box piles: rectangular or octagonal in
shape
• Formed by suitable combinations of
steel sections.
• In this type of steel piles, the tubes
are driven into the ground.
• The pipes are driven either with
open end or with closed end.Prof. Ashish Makwana 42

5. Timber Piles
Timber Piles
• Timber piles: prepared from
trunks of trees
• Common Indian timbers used for
piles: Babul, Chir, Deodar, Jarul,
Poon, Sal, Semul, Teak, White siris
and Khair
• Timber piles: circular or square
• Diameter of circular timber piles :
30 to 50 cm. and the side of a
square timber piles varies from 30
to 50 cm.
• Length of timber pile should not
exceed 20 times to its top width.

6. Wrought-iron piles
• These piles are generally made solid. The diameter varies
from 80 mm to 200 mm and the length is usually about 4
meters to 6 meters. The wrought-iron piles have suitable
devices for lengthening and sinking. These piles are mostly
used for shafts of screw piles.
• The wrought-iron piles are most suitable for use under sea
water. But as these piles are expensive, they are now replaced
by the steel piles.

2. NON-LOAD BEARING PILES

• This type of piles are used as separating members
below ground level and they are not generally
designed to take any vertical load. They are usually
sheet piles.
NON-LOAD BEARING PILES
Concrete sheet piles Steel sheet piles Timber sheet piles

Pre-cast RCC sheet piles
1. Concrete sheet piles
• Piles: always pre-cast
• Reinforcement: provided as per design
• Piles: square or rectangular in cross-section
• Width of precast RCC piles : 50 to 60 cm.
• Thickness: 20 to 60 mm.

2. Steel sheet piles
Arch web steel sheet piles
Built-up type &
Corrugated steel sheet piles
• Offsets are provided in
the Centre so as increase
the moment of inertia
• Greater resistance to
bending
• Offer greater resistance
to bending
• Similar to arch web type
• Depth of offset:
increased considerably
• Offer greater stiffness
Deep arch web steel sheet pilesProf. Ashish Makwana 48

Straight web
steel sheet piles
Universal joist steel sheet piles
• Simplest form of steel sheet
pile
• Width: 40 to 50 cm.
• Thickness from 10 to 12 mm
• Piles: consists of I-
beams connected by
standard clutches
Z-type steel sheet piles
• Z-type steel sheet
piles: difficult to roll
and to drive
• Possesses highest
beam strength
• Used for heavy work

3. Timber sheet piles
Timber sheet piles
• Wooden sheet piles are commonly used for temporary works,
such as cofferdams.
• Wooden boards 80 – 150 mm thick, 200 – 300 mm wide, 2 – 4
m long Prof. Ashish Makwana 50

Butt joint
Built up tongue and
groove joint
Built up dovetail joint
VARIOUS JOINTS OF
TIMBER SHEET PILES
• Butt joint: formed by Placing
timber boards in a single line
• Used for shallow excavations
• Pieces of timber: attached
to wooden boards to form
tongues and grooves
• Practically no wastage of
timbers when this is adopted
• superior to ordinary
dovetail joint

Ordinary dovetail joint
Lapped joint
Ploughed and
tongued joint
Splayed joint
• better than tongue and groove joint
• Adopted when wooden pile consists
of two boards
• better than tongue and groove joint
• Two boards are cut at ends in such
a way that when they are placed
together, a groove is formed.
• Requires more labour but it forms
an excellent joint
• Used for ordinary works

Ordinary tongued and
grooved joint
Vee joint
Wakefield joint
• Used for work of superior
nature
• Used for ordinary works
• Used where more strength and
water tightness are required.
• Consists of three boards which
are bolted together

Composite Piles
• Advantages:-
• Economical
• Easy to construct
• Suitable for ground conditions
in which other types of piles
will be unsuitable Prof. Ashish Makwana 54

Composite Piles
• A composite pile is formed when it is a combination either of a
bored pile and a driven pile or of driven piles of two different
materials.
• Process:
– A hollow steel tube is driven just below the lowest ground
water level.
– The tube is cleaned out.
– The timber pile is lowered into the steel tube and driven to
the required level.
– The tube is then filled with concrete and it is extracted by a
succession of upward extracting and downward tamping
blows.
Combination of materials:
wood and concrete
steel and concrete

Screw Piles
Shaft Dia. 80-250 mm
Blade
Dia. 500-1500 mm
Screw pile with gimlet point
Screw pile with blunt point Screw pile with hollow conical point
Screw pile with serrated point

Screw Piles
• A screw piles consists of a hollow cast-iron or steel cylinder
with one or more blades at the bottom.
• Types:
– Screw pile with blunt point
– Screw pile with gimlet point
– Screw pile with hollow conical point
– Screw pile with serrated point
• Situations when screw piles are used:
– To avoid shocks.
– To construct pile foundation of existing structures.
– To provide piles at places where it is not possible to install
heavy pile machinery.
– To provide foundations of marine structures, light bridges
etc.

Disc pile
Disc Pile
• Disc Pile: A steel pile having a disk on its lower end to give
increased supporting power.Prof. Ashish Makwana 58

Disc Pile:
• Consists of hollow cast-iron pipe with a disc
• Diameter of the disc: 60 – 130 cm
• To facilitate jetting of harder strata and tough soils
• Discs supported by a number of radial ribs
• Piles most useful in subsoil consisting of sands / sandy
silt
• Most useful for marine structures

PILE SPACING
• The spacing of pile is the center to center distance
between two piles.
• The factors to be considered while deciding the pile
spacing are as :
– The nature of soil through which the pile is driven
– The obstructions during pile driving
– The type of pile
– The depth of penetration
– The area of cross-section of the pile
– The center to center distance of piles in a group
– The manner in which the pile supports the load, i.e. whether the
pile acts as an end bearing pile or a friction pile or it acts both
ways
– The material of pile
– The damage to adjacent piles during pile driving operationProf. Ashish Makwana 60

PILE SPACING
Spacing criteria
- 2 times the diagonal dimension for square pile
- 2.5 times the diameter for circular or octagonal pile

GROUP OF PILES
• The piles forming the group of piles may be arranged in
square, rectangular, triangular or circular as per the
requirement.
• In case of friction piles, the center to center distance
between successive piles should be 105 cm. or the
perimeter of the pile, whichever is greater.
• In case of end-bearing piles, the center to center
distance between successive piles should be 75 cm. or
twice the width of the pile, whichever is greater.

GROUP OF PILESProf. Ashish Makwana 63

Typical arrangements of piles in groupsProf. Ashish Makwana 64

EFFICIENCY OF GROUP OF PILES
• The efficiency of a pile group is taken as the ratio of the
average load per pile, when failure of the group occurs to
the load at failure of a comparable single pile.
• The efficiency of pile group depends upon the various
factors, such characteristics of pile (i.e. length, diameter,
material, etc.), space of pile, total number of piles in a
row and number of rows, etc.
• Two rules used to find out efficiency of group of piles:
– Converse Labbore equation
– Feld rule

1. Converse Labbore equation:
2. Feld rule:
• The efficiency of a single pile is 100%
• If piles are arranged in group, there is reduction of 6% in
efficiency for each direction.
• Overall efficiency of group of piles is obtained by dividing
total efficiency of all the piles with the total number of piles.

PILE CAP AND PILE SHOES
Various types of piles
• When the RCC column or any load carrying structural
member is supported on more than one pile, the no. of
piles are connected through a pile cap to distribute the
load to the individual piles.

Pile Cap and Pile Shoe
Square pile shoe Wedge-shaped pile shoe
Round pile shoe
Steel strap pile shoe for
timber piles
Closed-end shoe for
pipe piles
Socket type shoe for
timber piles

Pile Cap
• Pile Cap should be extended beyond exterior piles by
10-15 cm.
• The pile should be embedded by at least 15 cm in the
pile cap.
• Reinforcement should be placed at least 10 cm above
pile head. Prof. Ashish Makwana 69

LOAD TESTS ON PILES
• The load tests on piles can be carried out by Pile load
method for determining the load carrying capacity of a
pile.
• The test load is applied with the help of a calibrated jack
plat; over a rigid circular or square plate, which may be
placed on the head of the pile projecting above ground
level. The reaction of the jack is borne by a truss or
platform, which may have gravity loading in the form of
sand bags, etc. or alternatively, the truss can be
anchored to the ground with the help of anchor piles.
• The load is applied in equal increments of about one-fifth
of the estimated allowable load. The settlements are
recorded with the help of three dial gauges of sensitivity
0.02 mm, symmetrically arranged over the test plate and
fixed to an independent datum bar.Prof. Ashish Makwana 70

• The test piles are loaded until ultimate load is reached.
Ordinarily, the test load is increased to a value 2.5 times
the estimated allowable load or to a load which causes a
settlement equal to one-tenth of the pile diameter,
whichever occurs earlier.
• The results are plotted in the form of load-settlement
curve. The ultimate load is clearly indicated by the load-
settlement curve approaching vertical.
• If the ultimate load cannot be obtained from the load
settlement curve, the allowable load is taken as follows :
– One-half to one-third the final load which causes settlement
equal to 10% of the pile diameter.
– Two-thirds of the final load which causes a total settlement of 12
mm or
– Two-thirds of final load which causes a net settlement (residual
settlement after the removal of load) of 6 mm.

a) Jack loading: Reaction by loaded platform

(b) Pile Load TestProf. Ashish Makwana 73

PILE DRIVING EQUIPMENTS
Light pile frame
1. Pile frames

1. Pile frames
• Mounted on standard tracked crane base machines for
mobility on land sites
• Light and easily transportable frames of tubular
construction
• All type of pile frames consists of leaders
• Ensure that the pile frame remains in its correct position
throughout the driving of a pile

2. Piling Winches
• Mounted on the base
• powered by steam, diesel or petrol engines or electric
motors
• Light winches: single drum, double and triple drum
winches
3. Helmet, driving cap, dolly and packing
• cast-steel helmet - placed over the top of a concrete pile,
to hold the dolly and packing
• Helmet should fit loosely around the pile.
• Dolly is placed in a square recess in the top of the
helmet.
Dollies are used for
- to moderate driving
- for hard driving a hard wood, such
as oak, green heart is usedProf. Ashish Makwana 77

Pile drive-cap / helmet
Section Elevation

Pile drive-cap / helmet
Hammer driving pile
• used to protect the heads of steel bearing piles

4. Jetting Piles
• water jetting - used to aid the penetration of a pile into a
sand / sandy gravel stratum
Pile with central jet pipe

5. Pile driving by Vibration
• Vibratory methods of driving sheet piles are best suited
to sand or gravel soil.
• Vibrators will drive steel piles through loose to medium
dense sands and gravels.
• Vibrators can also be used for extracting piles.

various types of pile
hammers
Drop hammers
Single — acting
steam hammers
Double — acting
steam hammers
Diesel hammers
Hydraulically
operated hammers
6. Piling hammers
The function of a piling hammers is to impart energy required
to drive a pile.

Variousfactors-
typeofpilehammers:
• Cost of purchase or hiring charges
• Available steam pressure
• Available head room
• Presence or absence of water
• Nature of work
• Material used for piles to driven
• Position of piles, i.e. vertical or inclined

1. Drop hammers:
- simplest form of hammer
Advantages:
(i) It is simple to operate.
(ii) Energy per blow can be varied by varying the height of
fall.
(iii) The initial cost is less.
Disadvantages:
(i) It is not easy to control the height of drop with any
accuracy.
(ii) There is danger that the operator will use too great a drop
when driving becomes difficult, it will increase the risk of
damage to the pile.

Fig.23 Pile driving with Drop hammer
(a) Side elevation (b) Front elevation

2. Single-acting steam hammers :
– consists of a massive weight in the form of a cylinder
– steam or compressed air admitted to the cylinder raises it up
the fixed piston rod
– At the top of the stroke, the steam is cutoff and the cylinder
falls freely on to the pile helmet.
– height of drop: 1.37 m and rate of 60 stroke per minute
Advantages :
(i) If the height of drop is limited to 1.2 m., the damage to the
pile can be avoided.
(ii) A blow delivered by a heavy hammer with a short drop is
much more effective and much less damaging to the pile.
Disadvantages :
(i) The concrete piles are liable to be shattered by a blow from
too great a height.
(ii) Special care is needed, when seating a pile on to a hard
bearing stratum, such as rock.Prof. Ashish Makwana 86

3. Double-acting steam hammers:
– used for sheet pile driving
– designed to import a rapid succession of blows to the pile
– rate of driving: 100 blows to 300 blows per minute
– mass of the ram: 2300 kg to 2700 kg. per blow
– driven by steam or compressed air
– drive under water to depths of 25 m.
Advantages :
• Pile frame is not required in this type of hammers. The
hammer is attached to the pile by leg-guides and a
timber framework is provided to guide the pile.
• It can be fitted with a chisel point for demolition and rock
breaking for extracting piling.
Disadvantages :
• Care is needed in their maintenance and lubrication and
during driving they must be kept in alignment with the
pile and prevented from bouncing.Prof. Ashish Makwana 87

4. Diesel hammers :
– The diesel hammers provide an efficient means of pile driving
in favorable ground conditions.
– It consists of a cylinder, an impact block, a piston, a fuel-tank
and simple fuel injection system.
– In this type of hammer, the falling ram compresses the air in
the cylinder and the impact atomize a pool of diesel oil, which
ignites with the compressed air and the resulting explosion
imparts an additional kick to the pile.
Advantages :
– These hammers can be economical as they dispense with
steam or compressed air plant and are entirely self contained.
Disadvantages :
– Diesel hammers are ineffective in soft or yielding soils, when
the impact of the blow is insufficient.
– These hammers may also cause breakage of precast concrete
piles, while driving through soft ground.

5. Hydraulically operated hammers :
• This type of hammers produce less noise and vibration.
• The ram is raised by hydraulic fluid and it falls freely on
to the pile.
• The operation of the hammer is by a valve which allows
either single-stroke working by manual control or
automatic striking.
• The B.S.P. hydraulic hammers have a striking rate of 40
blow min. and ram weights in the range of 3 to 7 tonnes.

PULLING OF PILES
The various reasons of pulling out of piles from their
positions are as follows :
(i) The piles are removed or pulled out, which are driven
temporarily, as in case of a cofferdam.
(ii) To replace the piles damaged during the driving
operations.
(iii) To prepare the data of the strata through which piles
are to be driven by carrying out pulling tests.
(iv) To reuse the existing piles, when the structure above
the pile is demolished or when the design of
arrangement of piles is changed.

• The methods adopted for pulling of piles may depend upon
the equipment available, type of pile, etc.
• The concrete piles cannot be pulled successfully without
damage and therefore they cannot be reused.
• On the other hand, the steel piles can be pulled out without
damage and they can be reused at other places.
• The water jet or compressed air or a combination of both may
be adopted to reduce the skin friction during pulling
operations.
The methods adopted are as follows :
1. Use of double-acting steam hammers :
The double-acting steam hammers are worked in a reverse
manner. It becomes necessary to apply a steady pull of 4
tonnes per cm2. in this method of pulling the piles.
2. Use of vibrators :
The vibrators are employed to pull out the piles. Due to the
vibrations, the soil surrounding the piles becomes loose and it
facilitates the removal of the pile.Prof. Ashish Makwana 91

3. Use of pile extractors :
– In this method, the specially designed pile extractors are
employed. The extractor can be put up into use immediately and
it does not require any special fitting.
4. Use of electricity :
– This method of pulling the piles is suitable for steel piles. A
direct current voltage is applied to steel pile for a short duration.
– The water present in the ground will be attracted towards the
surface of steel pile and thus it will lubricate the steel pile. The
skin friction will thus be reduced, resulting in easy removal of the
pile.
5. Use of tongs :
– The piles can be pulled by specially designed tongs. It is
suspended from a frame and with a pull of 50 tonnes or so, piles
can be pulled out.

LOADS ON PILES
• While designing a pile, the loads to be taken into account are as
follows :
– The direct vertical load to be transmitted by the pile.
– The stresses developed during handling operations.
– The bending stresses developed due to eccentricity of loads
coming on the pile.
– The bending stresses developed due to curvature of the pile.
– The lateral forces due to wind, waves, currents of water, etc.
– The forces due to impact of ships, in case of marine
structures.
– The impact stresses developed during the process of pile
driving.
– The impact forces due to ice sheets or bergs.
– The forces due to uplift pressure, if any.
– The earthquake forces, etc.Prof. Ashish Makwana 93

CAUSES OF FAILURES OF PILES
The most common causes of failures of piles are as follows :
– The actual load coming on the pile may be more than
the designed load.
– The bad workmanship in case of cast-in-situ cement
concrete piles.
– The attack by insects, etc. on wooden piles, causing
the decay of timber piles.
– The breakage due to overdriving especially in case of
timber piles.
– The damage due to abrasion resulting from the
absence suitable protective covering.

– The buckling of piles due to removal of side support,
inadequate lateral support, etc.
– The absence of statistical data regarding the nature of
strata through which piles are to be driven.
– The improper classification of soils.
– The improper choice of the type of pile.
– The improper choice of the method of driving the pile.
– The presence of soft strata just below the tips of piles.
– The lateral forces not being taken into the design of
the pile.
– The wrongful use of pile formula for determining its
load bearing capacity.
– The mis-interpretation of the results obtained during
test loads.

PILE DRIVING FORMULAS
1. Dynamic formulae :
– These are used for precast concrete piles. When a pile-
hammer hits the pile, the total driving energy is equal to
the weight of hammer times the height of stroke.
– In case of double acting hammers, some energy is also
imparted by the steam pressure during the return stroke.
– The total downward energy is consumed by the work
done in penetrating the pile and by certain losses. The
various dynamic formulae are essentially based on this
assumption. It is also assumed that soil resistance to
dynamic penetration of pile is the same as the
penetration of pile under static loading.

The following are some of the commonly used dynamic formulae.
(a) Engineering New Formula :
• The Engineering News Formula was proposed by AM
Wellington (1818) in the following general form :

The above formula reduces to the following forms :
(i) For Drop Hammers :
(ii) Single-acting steam Hammers:
(iii) Double-acting steam Hammers:
where, a = effective area of piston (cm2)
p = mean effective steam pressure (kg/cm2)

(b) Hiley's Formula (IS Formula) :
• Indian Standard IS : 2911 (Part-I) 1964 gives the
following formula based on original expression by Hiley :

2. Static Formulae
• The static formulae are based on the assumption that the
ultimate bearing capacity Qf of a pile is the sum of the total
ultimate skin friction Rf and total ultimate point or end bearing
resistance Rp.
• As = surface area of pile upon which the skin friction acts
• Ap = area of cross-section of the pile on which bearing
resistance acts
• For tappered piles, Ap may be taken as the cross-sectional
area at the lower one-third of the embedded length
• rf = average unit skin friction, which may be taken equal to
unit cohesion for cohesive soils
• rp = toe resistance

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