Pile foundation I

Uses of piles W

1. To carry vertical load

If all the (majority amount) loads are transferred to the pile tips

Soft soil
End bearing pile Friction

If all the (majority amount) loads are transferred to the soil along
the length of pile
Hard layer

Friction pile End bearing

Compaction pile: Short piles used for compacting loose sand.

 Tu
2. To resist uplift load

Tension pile or Uplift: Below some structures such as

transmission tower, offshore platform which are
subjected to tension.

Tension Pile
Murthy (2001)
3. To carry inclined and horizontal load
(foundation for retaining wall, bridge,
abutments and wharves)

Laterally loaded piles: Horizontal load acts

perpendicular to the pile axis.
Murthy (2001) W
H
Batter piles: Driven at an angle
Carry large horizontal load

Batter Pile
 Types of pile

Cross-section Shape Mode of Method of Method of Based on

Material used
• Circular • Cylindrical load transfer installation forming
• Steel pile displacement of soil
• Square • Tapered • End bearing • Driven • Pre-cast • Displacement piles
• Timber pile
• Hexagonal • Under-reamed • Friction • Bored • Pre-stressed • Non displacement
• Concrete pile
• I-section •Combined • Jetted • Cast in situ
• Composite pile piles
•H- section
•Pipe
 https://in.pinterest.com/pin/680 Steel Pile
Based on material used : 043612452541560/

http://www.86steelpipe.com/
Concrete Pile cs/gr-50-steel-pipe-piles.html

https://www.slideshare.net/shivamsgandhi/pile-foundation

Timber Pile
Timber pile: suitable for light loads varies from 100 to 250 kN per pile. Suitable for soft
cohesive soil.

Concrete Pile: all load condition. Most frequently used piles. Strong, durable.

Steel pile: Used to carry heavy load

Based on crosssection:

a) circular, b) square, c) rectangular, d) hexagonal,

e) H- section, f) pipe
Rock or very dense sand – H pile and open ended pipe pile (least driving effort)

Under the vertical load, the type of pile cross section does not play a important role.
However, under horizontal load, square and H section pile perform well as compared to
circular pile
Pile foundation II
Based on Shape:

Cylindrical Pile Tapered Pile

Underreamed Pile
Cohesive soil under laid by a granular soil – Cylindrical pile

Loose to medium dense granular soil – Tapered pile (for efficient transfer of load along the
length of pile.
efficient distribution of pile materials)
Expansive soil – Under-reamed pile
Under-reamed Pile:

• 150-200 mm shaft diameter

• 3 to 4 m long
• Underreamed portion is 2 to 3 times the shaft dia.
• Used for expansive soil
Punmia (1973)

a) Boring by auger
b) Under-reaming by under -reamer
c) Placing reinforcement cage in position
d) Concreting of pile
e) Concreting of pile caps
Mode of load transfer:

End- bearing pile

• Act as column
• Transmit the load through a weak soil to a hard stratum
• The ultimate load carried by pile= load carried by the bottom end

Friction pile
• Do not reach hard stratum
• Transfer the load through skin friction between embedded soil and pile
• The ultimate load carried by pile= load transferred by skin friction

Combined end- bearing and friction pile

•The ultimate load carried by pile= load transferred by skin friction + load carried by the
bottom end of pile
Method of installation
Driven Pile:
Bored Pile:
Driven Pile: loose granular soil (compact the soil, thus increase its shear resistance)

Bored pile: best suited to clay soil

Jetted pile: used if granular soil are in a very compact state

Method of forming
Precast concrete piles:

➢ Formed in a central casting yard to the specified length, cured and shipped to the
construction sites.
or
If space is available, casting yard may be provided at the site

➢Length upto 20m and precast hollow pipe piles can go up to 60m

➢ Shorter piles can carry load up to 600kN, and capacity of longer pile can be as large as
2000KN (in some cases)
Prestressed concrete piles:

Formed by tensioning high-strength steel (fult =1700 to 1860 MPa ) prestress cables and
casting the concrete pile about the cable

The prestress cables are cut, when the concrete hardens

Cast in situ pile

Formed by making a hole in the ground and filling it with concrete
If the hole is formed by drilling, then it is called bored cast in situ. If it is formed by driving a
metallic shell or a casing into the ground, then it is called driven cast in situ.
If during concreting the casing is left in position, then it is termed as cased pile. If the casing
is gradually withdrawn, then it is termed as uncased pile.
Precast and Prestressed pile: Use in marine structure.

Prestressed piles have large vertical load and bending moment capacity and are used in
such installation

Cast in-situ Pile: Soil of poor drainage quality

Suited in places where vibrations are avoided to save the adjoining structures
Based on displacement of soil:

Displacement Piles : All driven piles are displacement piles as the soil is displaced laterally
when the piles is installed.

Non-Displacement Piles : Bored piles are non- displacement piles

Advantages of precast concrete pile:

• Piles are cast in controlled environment

• The required number of piles can be cast in advance
• Loose granular soil is compacted
• The reinforcements remain in proper position.

Disadvantages of precast concrete pile:

• Addition reinforcements are required due handling and transportation

• Special equipments are required for handling and driving
• Piles can be damaged during handling and transportation
• If the soil is saturated, then pore water pressure is developed which reduces the
shear strength of the soil.
• Length adjustment is difficult
Advantages of cast-in-situ concrete pile:

• The length of the shell or pile can be increased or decreased

• No additional reinforcement is required
• Additional pile can be installed quickly
• Little chance of damage due to handling and transportation

Disadvantages of cast-in-situ concrete pile:

• Proper quality control

• Loose granular soil is not compacted significantly
• A lot of storage space is required for materials
Bored cast-in-situ piles: Large diameter pile can be made. Installation can be
made without appreciable noise or vibration. Boring may be loosen the granular
soil. In uncased pile, concreting is difficult due to the presence of drilling mud.
Bored piles are commonly cheaper. Length of the pile can be changed or varied
depending the ground condition.

Driven cast-in-situ piles: Diameter of the pile can not be made too large. More
noise and vibration . Granular soil is compacted . Drilling mud is not required. It is
costlier (especially the cased one). Length adjustment is difficult.
(Ranjan and Rao, 1991) Typical length and capacities of various piles:
Pile Type Pile length Approximate design load (kN)
Usual range Maximum Usual range Maximum
Timber 10-18 30 150-200 300
Driven precast concrete 10-15 30 300-600 900
Driven prestressed 20-30 60 500-600 900
concrete
Cast insitu concrete 15-25 40 300-750 900
(Drilled shell)
Concrete cast insitu 15-25 45(large dia.) 600-3000 9000 (large dia.)
bulb piles
Steel Pile 20-40 Unlimited 300-1000 2500-10000
(small dia.) (large dia.)
Composite Pile 20-40 60 300-900 2000
The information can be used only as a guide line during the initial planning and analysis stages
Pile foundation III
Pile load capacity in compression :

a) Static pile load formulae

b) Pile load tests

c) Pile driving formulae

d) Correlation with penetration test data

Static pile load formulae

The ultimate load capacity of the pile ( Qu)

Qu = Qpu + Q f

Q pu = Ultimate point load resistance of the pile

Qf = Ultimate skin friction

Qpu >> Qf point bearing pile or end bearing pile

Qf >>Q pu friction pile

The ultimate point load can be expressed in the form: Qpu = qpu Ab

Ab = sectional area of the pile at its base

The ultimate skin friction can be written in the form : Q f = fs As

fs = unit skin friction resistance

As= surface area of the pile in contact with soil

The ultimate load capacity (Q u) can be written in the form

Qu = qpu Ab + f s As
The general equation for unit point bearing resistance ( qpu) for c-ϕ soil :

q pu = cN c +  N q + 0.5BN 

where B = width or diameter of pile

σ’ = effective overburden pressure at the tip of the pile, equal to γL
N c , Nq, Nγ = bearing capacity factor
c = unit cohesion
L = length of embedment of pile
γ = effective unit weight of soil

In a deep foundation , σ'Nq >> 0.5γB Nγ . Hence, the third term is usually neglected

q pu = cN c +  N q
For a granular soil, c=c’=0 q pu =  N q

For a clay soil, c = c u and ϕu = 0 qpu = cub N c

c ub = undrained shear strength at the base of the pile

 Piles in granular soils:
Driven Piles:
Tomlinson's / Berezantsev’s Method
q pu =  ' Nq
 + 40∘
For a driven piles in sand c =
2
φc – in situ value of angle of shearing resistance

If φ > 40˚, Pile driving shall have the effect of reducing

the angle of shearing resistance of sand due to
dilatancy effect

The maximum base or tip or point bearing resistance Berezantsev’s Bearing Capacity factor
is limited to 11000 kN/ m2
Murthy (2001)
 Mayerhof (1976) Solution

qpu =  ' N q

Limiting value for point end bearing

qpul = 50Nq tan  kN / m

2
for dense sand
qpul = 25Nq tan  kN / m 2
for loose sand

Mayerhof (1976) bearing capacity factors Murthy (2001)

Skin friction:
f s =  h tan( )
f s = K ' tan( )

δ = angle of friction between the pile and the soil

K= the lateral earth pressure L σh σh
σh = the soil pressure acting normal to the pile surface (horizontal)
σ‘ = the effective vertical overburden pressure

Ultimate Skin friction resistance ( Qf ) :

Q f = fs (av) As
Q f = K av ' tan ( ) As

σ’av = average effective overburden pressure over the embedded length of the pile
 Broms (1966) recommends the value of K and δ shown in Table for piles driven into sand

Ranjan and Rao, 1991

Murthy (2001)
 Critical depth:
Depend on φ’ value and diameter of pile (D).
Critical depth may vary from
about 15D in loose to medium
sand to 20D in dense sand.

Limiting value for skin

Resistance in
homogenous sand
 The allowable load Q a : Qu
Qa =
F

Qu = ultimate load
F = factor of safety = 2.5

Note: The bored piles in sand have a point bearing or top resistance (qpu ) is 1 / 2
to 1 / 3 of the value of the driven piles. In case of bored pile in sand, the lateral
earth pressure coefficient can be calculated as: K = 1-sin . The value of K varies
from 0.3 to 0.75 (average value of 0.5). The  value is equal to  for bored piles
excavated in dry soil and a reduced value is considered if slurry has been used
during excavation.
 IS:2911(Part1): 2010
• Piles in granular soil 1  n
Qu = Ap  D N  + PD N q  +  K i PDi tan  i Asi
2  i=1
where A p =c/s area of pile tip
D= diameter of pile
Nq and N γ= bearing capacity factors depending on angle of internal friction
PD= effe ctive overburden pressure at pile tip
i= any layer between 1 to n layers in which pile is installed and it contributes to
positive skin friction
Ki= coefficient of earth pressure applicable in i th layer of soil .It depends on the
nature of soil strata, type of pile, spacing of pile and its method of construction.
For driven piles in loose to dense sand ( = 30 to 40), Ki value in the range of 1 to 2
may be used.
For bored piles in loose to dense sand ( = 30 to 40), Ki value in the range of 1 to 1.5
may be used.
 PDi= effective overburden pressure for i th layer
δi= angle of wall friction between soil and pile in i th layer (may be taken as )
Asi= surface area of pile shaft at i th layer

Note: As per IS Code [IS:2911(Part1/Sec 1):2010], for piles longer than 15 to 20 times
the pile diameter, maximum effective overburden stress at pile tip should
correspond to the pile length equal to 15 (if 30) to 20 (if 40) times of the
diameter.
 IS 6403:1981
φ(in Nγ
degree)

0 0
• Nγ factor can be taken for general shear failure 5 0.45
according to IS 6403.
• N factor will depend on the nature of soil, type of 10 1.22

piqle, the L/D ratio and its method of construction. 15 2.65

The values applicable for driven piles are given in 20 5.39
this figure. 25 10.88
30 22.40
35 48.03
40 109.41
45 271.76
50 762.89
 IS:2911(Part1 / Sec 1): 2010 IS:2911(Part I / Sec2): 2010

Driven precast and cast in situ concrete pile Bored precast and cast in situ concrete pile
Pile foundation IV
Example: (a) A 15m long, 300 mm diameter pile was driven in a uniform sand (’= 40).
The water table is at great depth. Average unit weight of soil is 19 kN/ m3. Calculate the
safe load capacity of the pile with F.O.S =2.5.
(b) Calculate the safe load capacity of the pile if water table is located at 2m below
the ground level.
 Piles in granular soils:
Driven Piles:
Tomlinson's / Berezantsev’s Method
q pu =  ' Nq
 + 40∘
For a driven piles in sand c =
2
φc – in situ value of angle of shearing resistance

If φ > 40˚, Pile driving shall have the effect of reducing

the angle of shearing resistance of sand due to
dilatancy effect

The maximum base or tip or point bearing resistance Berezantsev’s Bearing Capacity factor
is limited to 11000 kN/ m2
Murthy (2001)
 Mayerhof (1976) Solution

qpu =  ' N q

Limiting value for point end bearing

qpul = 50Nq tan  kN / m

2
for dense sand
qpul = 25Nq tan  kN / m 2
for loose sand

Mayerhof (1976) bearing capacity factors Murthy (2001)

 Broms (1966) recommends the value of K and δ shown in Table for piles driven into sand

Ranjan and Rao, 1991

Murthy (2001)
 IS:2911(Part1): 2010
• Piles in granular soil 1  n
Qu = Ap  D N  + PD N q  +  K i PDi tan  i Asi
2  i=1
where A p =c/s area of pile tip
D= diameter of pile
Nq and N γ= bearing capacity factors depending on angle of internal friction
PD= effe ctive overburden pressure at pile tip
i= any layer between 1 to n layers in which pile is installed and it contributes to
positive skin friction
Ki= coefficient of earth pressure applicable in i th layer of soil .It depends on the
nature of soil strata, type of pile, spacing of pile and its method of construction.
For driven piles in loose to dense sand ( = 30 to 40), Ki value in the range of 1 to 2
may be used.
For bored piles in loose to dense sand ( = 30 to 40), Ki value in the range of 1 to 1.5
may be used.
 IS 6403:1981
φ(in Nγ
degree)

0 0
• Nγ factor can be taken for general shear failure 5 0.45
according to IS 6403.
• N factor will depend on the nature of soil, type of 10 1.22

piqle, the L/D ratio and its method of construction. 15 2.65

The values applicable for driven piles are given in 20 5.39
this figure. 25 10.88
30 22.40
35 48.03
40 109.41
45 271.76
50 762.89
 IS:2911(Part1 / Sec 1): 2010 IS:2911(Part I / Sec2): 2010

Driven precast and cast in situ concrete pile Bored precast and cast in situ concrete pile
Pile foundation V
Example: (a) A 15m long, 300 mm diameter pile was driven in a uniform sand (’= 40).
The water table is at great depth. Average unit weight of soil is 19 kN/ m3. Calculate the
safe load capacity of the pile with F.O.S =2.5.
(b) Calculate the safe load capacity of the pile if water table is located at 2m below
the ground level.
 Piles in granular soils:
Driven Piles:
Tomlinson's / Berezantsev’s Method
q pu =  ' Nq
 + 40∘
For a driven piles in sand c =
2
φc – in situ value of angle of shearing resistance

If φ > 40˚, Pile driving shall have the effect of reducing

the angle of she aring resistance of sand due to
dilatancy effect

The maximum base or tip or point bearing resistance Berezantsev’s Bearing Capacity factor
is limited to 11000 kN/m 2
Murthy (2001)
 Mayerhof (1976) Solution

qpu =  ' N q

Limiting value for point end bearing

qpul = 50Nq tan  kN / m

2
for dense sand
qpul = 25Nq tan  kN / m 2
for loose sand

Mayerhof (1976) bearing capacity factors Murthy (2001)

 Broms (1966) recommends the value of K and δ shown in Table for piles driven into sand

Ranjan and Rao, 1991

Murthy (2001)
 IS:2911(Part1): 2010
• Piles in granular soil 1  n
Qu = Ap  D N  + PD N q  +  K i PDi tan  i Asi
2  i=1
where Ap=c/s area of pile tip
D= diameter of pile
Nq and Nγ= bearing capacity factors depending on angle of internal friction
PD= effe ctive overburden pressure at pile tip
i= any layer between 1 to n layers in which pile is installed and it contributes to
positive skin friction
Ki= coefficient of earth pressure applicable in i th layer of soil .It depends on the
nature of soil strata, type of pile, spacing of pile and its method of construction.
For driven piles in loose to dense sand ( = 30 to 40), Ki value in the range of 1 to 2
may be used.
For bored piles in loose to dense sand ( = 30 to 40), Ki value in the range of 1 to 1.5
may be used.
 IS 6403:1981
φ(in Nγ
degree)

0 0
• Nγ factor can be taken for general shear failure 5 0.45
according to IS 6403.
10 1.22
• Nqfactor will depend on the nature of soil, type of
pile, the L/D ratio and its method of construction. 15 2.65
The values applicable for driven piles are given in 20 5.39
this figure. 25 10.88
30 22.40
35 48.03
40 109.41
45 271.76
50 762.89
 IS:2911(Part1 / Sec 1): 2010 IS:2911(Part I / Sec2): 2010

Driven precast and cast in situ concrete pile Bored precast and cast in situ concrete pile
Pile foundation VI
 With and without
considering critical
length concept: Layered
soil
 Piles in granular soils:
Driven Piles:
Tomlinson's / Berezantsev’s Method
q pu =  ' Nq
 + 40∘
For a driven piles in sand c =
2
φc – in situ value of angle of shearing resistance

If φ > 40˚, Pile driving shall have the effect of reducing

the angle of she aring resistance of sand due to
dilatancy effect

The maximum base or tip or point bearing resistance Berezantsev’s Bearing Capacity factor
is limited to 11000 kN/m 2
Murthy (2001)
 Mayerhof (1976) Solution

qpu =  ' N q

Limiting value for point end bearing

qpul = 50Nq tan  kN / m

2
for dense sand
qpul = 25Nq tan  kN / m 2
for loose sand

Mayerhof (1976) bearing capacity factors Murthy (2001)

 Broms (1966) recommends the value of K and δ shown in Table for piles driven into sand

Ranjan and Rao, 1991

Murthy (2001)
 IS:2911(Part1): 2010
• Piles in granular soil 1  n
Qu = Ap  D N  + PD N q  +  K i PDi tan  i Asi
2  i=1
where Ap=c/s area of pile tip
D= diameter of pile
Nq and Nγ= bearing capacity factors depending on angle of internal friction
PD= effe ctive overburden pressure at pile tip
i= any layer between 1 to n layers in which pile is installed and it contributes to
positive skin friction
Ki= coefficient of earth pressure applicable in i th layer of soil .It depends on the
nature of soil strata, type of pile, spacing of pile and its method of construction.
For driven piles in loose to dense sand ( = 30 to 40), Ki value in the range of 1 to 2
may be used.
For bored piles in loose to dense sand ( = 30 to 40), Ki value in the range of 1 to 1.5
may be used.
 IS 6403:1981
φ(in Nγ
degree)

0 0
• Nγ factor can be taken for general shear failure 5 0.45
according to IS 6403.
10 1.22
• Nqfactor will depend on the nature of soil, type of
pile, the L/D ratio and its method of construction. 15 2.65
The values applicable for driven piles are given in 20 5.39
this figure. 25 10.88
30 22.40
35 48.03
40 109.41
45 271.76
50 762.89
 IS:2911(Part1 / Sec 1): 2010 IS:2911(Part I / Sec2): 2010

Driven precast and cast in situ concrete pile Bored precast and cast in situ concrete pile
 Piles in clay :
The ultimate load capacity of pile (Q u):

Qu = qpu Ab + f s As
In clays, qpu = c u N c and fs = c a = αcu

Qu = cub Nc Ab + cu As

c ub = undrained cohesion at the base of pile

Nc = bearing capacity factor for a deep foundation . For circular and square piles Nc = 9
(proposed by Skempton). Pile must go at least 5D inside the bearing stratum.
α = adhesion factor
c u = undrained cohesion in the embedded length of pile
Values of reduction factor α Murthy (2001)

cu (kPa) consistency
0 – 12.5 very soft
12.5-25 soft
25-50 medium
50-100 stiff
100-200 very stiff
>200 hard
Ranjan and Rao, 1991
Pile foundation VII
 IS:2911(Part1): 2010
• Piles in granular soil 1  n
Qu = Ap  D N  + PD N q  +  K i PDi tan  i Asi
2  i=1
where Ap=c/s area of pile tip
D= diameter of pile
Nq and Nγ= bearing capacity factors depending on angle of internal friction
PD= effe ctive overburden pressure at pile tip
i= any layer between 1 to n layers in which pile is installed and it contributes to
positive skin friction
Ki= coefficient of earth pressure applicable in i th layer of soil .It depends on the
nature of soil strata, type of pile, spacing of pile and its method of construction.
For driven piles in loose to dense sand ( = 30 to 40), Ki value in the range of 1 to 2
may be used.
For bored piles in loose to dense sand ( = 30 to 40), Ki value in the range of 1 to 1.5
may be used.
 IS:2911(Part1 / Sec 1): 2010 IS:2911(Part I / Sec2): 2010

Driven precast and cast in situ concrete pile Bored precast and cast in situ concrete pile
 Piles in clay :
The ultimate load capacity of pile (Q u):

Qu = qpu Ab + f s As
In clays, qpu = c u N c and fs = c a = αcu

Qu = cub Nc Ab + cu As

c ub = undrained cohesion at the base of pile

Nc = bearing capacity factor for a deep foundation . For circular and square piles Nc = 9
(proposed by Skempton). Pile must go at least 5D inside the bearing stratum.
α = adhesion factor
c u = undrained cohesion in the embedded length of pile
Values of reduction factor α Murthy (2001)

cu (kPa) consistency
0 – 12.5 very soft
12.5-25 soft
25-50 medium
50-100 stiff
100-200 very stiff
>200 hard
Ranjan and Rao, 1991
 Qu
The allowable load Q a : Qa =
F

Qu = ultimate load
F = factor of safety = 2.5
Example: A 15 m long pile with diameter 400mm was driven in a homogeneous
clay with unconfined compressive strength of 100 kPa. Calculate the ultimate
load Carrying capacity of the pile.

Example: Layered soil (only Clay)

Values of reduction factor α Murthy (2001)

cu (kPa) consistency
0 – 12.5 very soft
12.5-25 soft
25-50 medium
50-100 stiff
100-200 very stiff
>200 hard
Ranjan and Rao, 1991
• Piles in cohesive soil [IS:2911(Part1): 2010]
n
Qu = A p N c c p +   i c i Asi
i =1

where Ap= c/s area of pile tip

Nc = bearing capacity factor may be taken as 9
cp = average cohesion at pile tip
αi= adhesion factor for i th layer
c i= average cohesion at i th layer
Asi= surface area of pile shaft at i th layer
Pile foundation VIII
Example: Layered soil (Sand-Clay)
Load carrying capacity of under-reamed pile in Clay
D

Qu = cub Nc Ab + c'u As = (9cub ) D12 + c'u As
4
Nc = 9
D1
α = adhesion factor
Ab = area of the enlarge base
D1 = diameter of the bulb
Note: When the bulb is slightly above the tip, Ab is equal to the area of the
diameter of the bulb and the projected stem below the bulb is ignored.
If bulb is quite high : D

For single bulb

 2 
Qu = (9cub ) D +  9c' ub (D12 − D 2 )+ c' u As
4 4 D1

c ub = unit cohesion at the tip

c’ ub = unit cohesion at the bulb level
c'u = average cohesion on A s
A’s = surfac e area
= The length of the shaft equal to 2D above the bulb is usually neglected
(As the pile settles, there is possibility of formation of a small gap between the top of bulb)
Two or more bulbs D

 2 
Qu = (9cub ) D +  9c' ub ( 1
D 2
− D 2
)+ c'u As + c"u Asb
4 4
c ub = unit cohesion at the tip D1
c’ ub = unit cohesion at the bulb level
As = surface area of the shaft above the top bulb (ignoring 2B length)
Asb = surfac e area of the cylinder circumscribing the bulbs between top
and bottom bulbs D1
c'u = average cohesion on A s
c” u = average cohesion on Asb
 Pile Load test
• It is the only direct method for determining the allowable load on piles.

• It is an in-situ test and the most reliable one also.

• It is very useful for cohesion less soil.

• However, for cohesive soil, data from pile load test should be used with caution because
of pile driving disturbanc e, pore water pressure development, and inadequate time
allowed for the consolidation settlement.
 Types of load test

Vertical load test Lateral load test Pull out test

(compression) (Tension)

➢ It is carried out to esta blish

load- settlement relationship
under compression and ➢These two tests are carried out when piles are
determine the allowable load on required to resist the lateral loads or uplift loads .
pile.
 Initial test

It is to be carried out on test piles to estimate the allowable load, or to

predict the settlement at working load. It does not carry any load coming
from superstructure .

Where there is no specific information about subsoil strata and no past

experience, for a project involving more than 200 piles, there should be
minimum two initial tests.

The minimum load on test piles should be twice the safe load or the load at which total
settlement attains a value of 10% of pile diameter for single pile and 40 mm in group.
 Routine test

It is carried out as a check on working pile to assess the displacement

corresponding to working load.

The minimum no. of routines tests should be half percentage of the piles used. It
may vary up to 2 percent or more depending upon the nature of soil strata and
importance of structure .

A working pile is driven or cast in situ along with other piles to carry the load from
superstructure . The load on such piles should be up to 1.5 times the safe load or the load at
which the total settlement attains 12mm for single pile and 40 mm for group pile ,
whichever is earlier.
 Pile load test
Types of Load test

Continuous loading Cyclic loading

Load is raised to a particular level

Continuous increment of load is applied and then dropped to zero, again
on the pile head increased to a higher level and
reduced to zero.
 Procedure: As per IS: 2911 part IV (1979)

• The test shall be carried out by applying the

load on a RCC cap over the pile.
• The load is applied in increment of 20 % of
Step 1 the safe load .

• Settlements are recorded with at least three

dial gauges.
Step 2

• Each stage of loading shall be maintaining

till the rate of movement of pile top is not
Step 3 more than 0.1 mm /hr.
Pile foundation IX
The allowable load on a single pile shall be lesser of the following:

• 2/3rd of final load at which the total settlement attains a value of 12mm. If nothing
is specified, then the permissible settlement =12mm. If any other permissible value
is specified, then load shall correspond to actual permissible total settlement.

• 50% of final load at which the total settlement equals to 10% of the pile diameter
in case of uniform diameter piles and 7.5% of bulb diameter in case of under
reamed piles.
The allowable load on a group of piles shall be lesser of the following:

• Final load at which the total settlement attains a value of 25mm. The permissible
settlement is 25mm.

• 2/3rd of the final load at which the total settlement attains a value of 40mm.
Example: The following data was obtained in a vertical pile load test on 300 mm diameter pile.
Determine the allowable or safe load as per IS 2911 part IV (1979).

Load (kN) Settlement (mm) 0 100 200 300 400 500 600 700
50 2.5 0
100 5.0 10
200 10.0 20
300 17
30
400 28
500 45 40

600 70 50

60

70

80
Vertical cyclic plate load test:

• It is carried out when it is required to separate the pile load into skin friction and point
bearing on single piles of uniform diameter.

• It is limited to initial tests only.

Pile foundation IX
The allowable load on a single pile shall be lesser of the following:

• 2/3rd of final load at which the total settlement attains a value of 12mm. If nothing
is specified, then the permissible settlement =12mm. If any other permissible value
is specified, then load shall correspond to actual permissible total settlement.

• 50% of final load at which the total settlement equals to 10% of the pile diameter
in case of uniform diameter piles and 7.5% of bulb diameter in case of under
reamed piles.
The allowable load on a group of piles shall be lesser of the following:

• Final load at which the total settlement attains a value of 25mm. The permissible
settlement is 25mm.

• 2/3rd of the final load at which the total settlement attains a value of 40mm.
Example: The following data was obtained in a vertical pile load test on 300 mm diameter pile.
Determine the allowable or safe load as per IS 2911 part IV (1979).

Load (kN) Settlement (mm) 0 100 200 300 400 500 600 700
50 2.5 0
100 5.0 10
200 10.0 20
300 17
30
400 28
500 45 40

600 70 50

60

70

80
Vertical cyclic plate load test:

• It is carried out when it is required to separate the pile load into skin friction and point
bearing on single piles of uniform diameter.

• It is limited to initial tests only.

Pile foundation X
 Dynamic Pile formula
• Engineering News Record Formula (ENR)
Energy input= Work done
Qu S  = WH

From above formula, the allowable pile load is expressed as

WH
Qa =
F (S + C)

W= weight of the hammer falling through a height, H

S’= Theoretical set= S+C
S= real set per blow
C= empirical factor allowing reduction in theoretical set due to energy losses
F= factor of safety (usually taken as 6)
http://hammer.m88play.com/drop-hammer-pile-driver/
 WH
a) Drop hammer Qa =
6(S + 2.5)
WH
b) Single acting steam hammers Qa =
6(S + 0.25)

(W + ap)H
c) Double acting steam hammers Qa =
6(S + 0.25)

where W (weight of hammer) and Q a are expressed in kg. H is the height of free fall of
hammer in cm. a is the effective area of piston in cm 2 and p is the mean effective steam
pressure in kg/cm 2 . S is the final set in cm/blow, usually taken as average penetration for the
last 5 blows of a drop hammer or 20 blows of a ste am hammer.
Example: A 250 diameter pile was driven with a drop hammer of weight 2200 kg
and having a free fall of 1.5m. The total penetration of the pile recorded in the
last 5 blows was 30mm. Determine the safe pile load using ENR.
 • Modified Hiley Formula
Actual Energy delivered= Energy used + Energy losses

Whh
Qu =
S +C2
Whh
=
S + (C 1 + C 2 + C 3 )
1
2

where Qu= ultimate driving resistance in tonnes. Safe load is estimated by dividing the
ultimate resistanc e by a factor of safety 2.5.
W= weight of hammer in tonnes.
h= effective fall of hammer, in cm
η= efficiency of blow that represents the ratio of energy after impact to striking
energy of ram.
ηh=hammer efficiency
S= final set or penetration per blow in cm.
C= total elastic compression= C 1+ C 2 +C 3
 • When W> Pe and pile is driven into penetrable ground,

W + Pe2
=
W +P
• When W< Pe and pile is driven into penetrable ground,
2
W + Pe 2 W − Pe 
= − 
W +P  W +P 
 

where P= weight of pile + anvil+ helmet +follower (if any) in tonnes

e= coefficient of restitution of material under impact and ranges from 0 to 1.
 C1 C2 C3

It is temporary elastic compression of It is temporary elastic It is temporary compression of

dolly and packing. compression of pile. soil.

Qu
= 1.77 Qu L
A = 0.675 Qu
A = 3.55
where the driving is with 2.5cm thick A
where L is length of pile in meter.
where A is area of pile in cm2.
cushion only on head of pile A is area of pile in cm2.
Qu
= 9.05
A
where the driving is with short dolly upto
60cm long, helmet and 7.5cm thick cushion
Murthy (2001)
Pile foundation XI
Correlation with penetration test data
• Driven piles in sand
1. Using Cone Penetration resistance

• The unit point resistance of driven pile q pu = static cone resistanc e q c

• The skin friction resistanc e for driven piles can also be determined with
help of cone penetration resistanc e using Meyerhof(1956) correlation:

For Displacement piles, q (av)

fs = c kN / m 2
(limited to 100 kN/m2)
2
For H piles, q (av)
kN / m 2 (limited to 50 kN/m2)
fs = c
4
where q c ( av )= average field value of cone penetration resistance in kg/cm 2 over pile length.
 • Using of static cone penetration data
[IS:2911(Part1 /Sec 1):2010]
For non homogeneous soil,
The ultimate point bearing capacity
can be taken as

 q c0 + q c1 
  + q c2
q pu = 
2 
2

qc0 is the average cone resistanc e

qc1 is the minimum cone resistanc e
qc2 is the average of minimum cone resistanc e
Using of static cone penetration [IS:2911(Part1 /Sec 1):2010]

Side or skin friction (fs) in kN/m2

qc 2q
 fs  c for clay
25 25
qc q
 fs  c for silty clay and silty sand
100 25
qc 2q
 fs  c for sand
100 100

qc q
fs  c for coarse sand and gravel
100 150
Example: Determine the allowable load carrying capacity of a
11 m long and 450 mm diameter driven pile constructed in the
sand with cone resistance (SCPT) profile as shown in the figure.
Pile foundation XII
2. Using N value:
• The unit penetration resistance of driven pile in sand including H pile can be determined as:

q pu = 40N (L D) kN / m 2

where N= standard penetration resistance observed in field without overburden correction

L= length of the pile
D= diameter of pile
For driven piles, qpu is limited to 400 N kN/m2.

• The skin friction resistance for driven pile in sand can be determined as:
For displacement piles: (limited to 100 kN/m2)
f s = 2N av kN / m 2
(Driven Piles)
For H piles: f s = N av kN / m 2 (limited to 50 kN/m2)

where N av = average field value of N along pile length

• Using of standard penetration data [IS:2911(Part1 /Sec 1):2010]
➢ For saturated cohesionless soil, the ultimate load bearing capacity of pile in kN is given by

Lb NAs
Qu = 40N Ap + For driven piles, qpu is limited to 400 N kN/m2.
D 0.5
where N= average N value at tip
Lb=length of penetration in bearing strata , in m
d= diameter of pile in m
Ap= c/s area of pile tip in m 2
N= average N value along pile shaft
As= surface area of shaft in m 2

➢ for non plastic silt or very fine sand, Lb NAs

Qu = 30N Ap +
D 0.6
• Bored and cast in situ piles in sand 1
q pu = q pu of driven pile
3
1
fs = f s of driven pile
2
• Driven and cast in situ piles in sand
For cased pile: q pu and fs can be taken same as that of driven pile.
fs = fs of driven pile (if proper compaction of concrete is done)
For uncased pile:
fs = fs of bored cast in situ (if proper compaction of concrete is not done)
 Group action of piles:

Pile cap

Soil

Pile group

https://www.deltares.nl/en/software/module/d-pile-group-cap- https://theconstructor.org/geotechnical/foundations/pile/page
layered-soil-interaction-3/ /2/
 • Ultimate bearing capacity of pile group≠ sum of all individual piles present in the group.
• Group efficiency, Qug
g =
nQu

where Qug= ultimate load bearing capacity of pile group

Qu= ultimate load bearing capacity of single pile
n= no. of piles

✓ ηg< 1 for smaller spacing between piles

✓ ηg >1 for driven piles in loose to medium soil
✓ ηg=1 for larger sp acing of piles
Pile group efficiency can be calculated using Converse- Labarre formula:
where m= no. of rows of piles
 m(n − 1) + n(m − 1)   n= no. of piles in a row
g = 1 −   −1 D 
 mn  90 θ= tan  
S
D= Diameter of pile
Minimum pile spacing S= Centre to centre spacing

Length of pile Friction piles in Friction piles in Point bearing

sand clay pile
< 12m 3D 4D 3D
12 to 24 m 4D 5D 4D
> 24m 5D 6D 5D

As per IS: 2911-I-1979 Bearing pile- 2 D

Friction pile- 3D
Loose sand or fill deposit -2D
Pile group in clay
Pile may fail in one of the following way
• By block failure (when spacing is less than 2-3 times diameter of a pile)
• By individual pile failure ( when piles are spaced wider)

• The ultimate load capacity of the pile group by block failure is given by:

Qug = cub Nc Ab + PbLcu

Undrained strength
Undrained strength of clay along length of block
of clay at base of Bearing capacity
pile group Embedded length of pile
factor= 9 Perimeter of block
c/s area of block
• The ultimate load capacity of the pile group by individual pile failure is given by:

Qug = nQu
Example: Determine the spacing of a group of 16 piles with diameter of 300mm such that the
efficiency of the pile group is 1. The piles were constructed in uniform clay soil with unconfined
compressive strength of 50 kPa.
 Settlement of a pile group
• Pile group in clay
1. For the displacement piles or friction piles in homogeneous clay

 1−  2 
Si = qn B I f
 E 

where qn= Net pressure on pile

μ= Poisson’s ratio
E= young’s Modulus
If= Influenc e factor
Consolidation settlement
 p + p 
Sc = 
Cc 
H log10  0
1+ e0  p0 
or Sc =  mv Hp

Where p 0 = initial effective overburden pressure before applying foundation load

∆p= vertical stress at the centre of the layer due to application of load
C c = Compression index
e0= initial void ratio
mv= coefficient of volume compressibility
H= thickness of each layer
2. Piles driven into a firm or strong stratum through an overlying clay stratum.
3. For bored piles or end bearing piles bearing on firm stratum

Equivalent raft acts at the base of the pile.

 • Pile group in sand
➢ Skempton (1953):
For same average load Q/pile acting in driven piles, the settlement ratio of group of pile to
single pile can be obtained as:
S g  4B + 2.7  2
= 
Si  B + 3.6 
where B= width of the pile group in ‘meter’
Sg= settlement of pile group
Si= settlement of single pile
➢ Meyerhof (1959):
It is for square pile groups driven in sand
Sg S (5 − S 3)
=
2
Si  1
1 + 
 r
where S= ratio of pile spacing to pile diameter
r= no. of rows in the pile group
Example: The following data was obtained in a vertical pile load test on 300 mm diameter pile.
Determine the allowable or safe load as per IS 2911 part IV (1979).

Load (kN) Settlement (mm) 0 100 200 300 400 500 600 700
50 2.5 0
100 5.0 10
200 10.0 20
300 17
30
400 28
500 45 40

600 70 50

60

70

80
Pile Foundation XIII
Example: Design a pile group consisting of RCC piles for a column of size 650mm × 650 mm carrying
a load of 1500 kN (Total). The exploration data reveal that the sub-soil consists of deposit of clay
extending to a greater depth. The other data of the deposit are: Compression index = 0.10, Initial
void ratio = 0.9, Saturated unit weight = 20 kN/m3, Unconfined compressive strength= 70kN/m2.
Proportion the pile group for the permissible settlement of 40 mm. Design the pile group by
considering both bearing and settlement criteria. The water table is considered at the ground level.
Use a factor of safety 2.5 against bearing and assume adhesion factor of 0.7.
Values of reduction factor α Murthy (2001)

cu (kPa) consistency
0 – 12.5 very soft
12.5-25 soft
25-50 medium
50-100 stiff
100-200 very stiff
>200 hard
Ranjan and Rao, 1991
Fox’s Correction Curves
Pile Foundation XIV
Negative skin friction:
Negative skin friction in single piles
The magnitude of negative skin friction, F n for a single pile may be estimated as below:
Cohesive soils:
Fn = PLcca
Where, P= perimeter of pile
L c = Length of pile in compressible stratum
c a = unit adhesion=αc u
α= adhesion factor
cu= undrained cohesion of compressible layer

Cohesionless soils: 1
Fn = PLc 2 K tan 
2

where K=lateral earth pressure coefficient

δ= angle of friction between pile and soil (1/2 φ to 2/3φ)
Negative skin friction in pile groups
The magnitude of negative skin friction, Fng for a pile group passes through soft and
unconsolidated soil may be estimated as below:

Fng = nFn Higher of value from these two Equation is

used in design
Fng = cu Lc Pg + Lc Ag

where n= number of piles in the group

Pg= perimeter of group
γ= unit weight of soil within pile group up to a depth of Lc
Ag= area of pile group within perimeter P g

Ultimate load capacity of a sin gle or a group of piles

F.O.S =
Working load + negative skin friction
 • Using of static cone penetration data
[IS:2911(Part1 /Sec 1):2010]
For non homogeneous soil,
The ultimate point bearing capacity
can be taken as

 q c0 + q c1 
  + q c2
q pu = 
2 
2

qc0 is the average cone resistanc e

qc1 is the minimum cone resistanc e
qc2 is the average of minimum cone resistanc e