Course
Year
Version
: S0484/Foundation Engineering
: 2007
: 1/0
Session 17 – 18
PILE FOUNDATIONS
PILE FOUNDATIONS
Topic:
• Types of pile foundation
• Point bearing capacity of single pile
• Friction bearing capacity of single pile
• Allowable bearing capacity of single pile
INTRODUCTION
TYPES OF PILE FOUNDATION
STEEL PILE
TYPES OF PILE FOUNDATION
CONCRETE PILE
TYPES OF PILE FOUNDATION
CONCRETE PILE
TYPES OF PILE FOUNDATION
TYPES OF PILE FOUNDATION
WOODEN PILE
TYPES OF PILE FOUNDATION
COMPOSITE PILE
COMBINATION OF:
- STEEL AND CONCRETE
- WOODEN AND CONCRETE
- ETC
PILE CATEGORIES
Classification of pile with respect to load transmission and functional behaviour:
1. END BEARING PILES
These piles transfer their load on to a firm stratum located at a
considerable depth below the base of the structure and they derive
most of their carrying capacity from the penetration resistance of the
soil at the toe of the pile
2. FRICTION PILES
Carrying capacity is derived mainly from the adhesion or friction of the
soil in contact with the shaft of the pile
3. COMPACTION PILES
These piles transmit most of their load to the soil through skin friction. This
process of driving such piles close to each other in groups greatly reduces
the porosity and compressibility of the soil within and around the groups.
PILE CATEGORIES
END BEARING PILE
PILE CATEGORIES
FRICTION PILE
PILE CATEGORIES
Classification of pile with respect to effect on the soil
- Driven Pile
Driven piles are considered to be displacement piles. In the process of
driving the pile into the ground, soil is moved radially as the pile shaft enters
the ground. There may also be a component of movement of the soil in the
vertical direction.
PILE CATEGORIES
Classification of pile with respect to effect on the soil
- Bored Pile
Bored piles(Replacement piles) are generally considered to be nondisplacement piles a void is formed by boring or excavation before piles is
produced.
There are three non-displacement methods: bored cast- in - place piles,
particularly pre-formed piles and grout or concrete intruded piles.
PILE CATEGORIES
DETERMINATION OF PILE LENGTH
BEARING CAPACITY OF PILE
Two components of pile bearing capacity:
1. Point bearing capacity (QP)
2. Friction bearing capacity (QS)
QU  QP  QS
BEARING CAPACITY OF PILE
POINT BEARING CAPACITY
For Shallow Foundation
- TERZAGHI
SQUARE FOUNDATION
qu = 1,3.c.Nc + q.Nq + 0,4..B.N
CIRCULAR FOUNDATION
qu = 1,3.c.Nc + q.Nq + 0,3..B.N
- GENERAL EQUATION
qu  c.Nc.Fcs .Fcd .Fci  q.Nq.Fqs .Fqd .Fqi  0,5. .B.N .Fs .Fd .Fi
Deep Foundation
qu = qP = c.Nc* + q.Nq* + .D.N*
Where D is pile diameter, the
3rd part of equation is
neglected due to its small
contribution
qu = qP = c.Nc* + q’.Nq* ; QP = Ap .qp = Ap (c.Nc* + q’.Nq*)
Nc* & Nq* : bearing capacity factor by Meyerhoff, Vesic and Janbu
Ap : section area of pile
POINT BEARING CAPACITY
MEYERHOFF
PILE FOUNDATION AT UNIFORM SAND LAYER (c = 0)
QP = Ap .qP = Ap.q’.Nq*  Ap.ql
ql = 50 . Nq* . tan  (kN/m2)
Base on the value of N-SPT :
qP = 40NL/D  400N
(kN/m2)
Where:
N = the average value of N-SPT
near the pile point (about 10D
above and 4D below the pile
point)
POINT BEARING CAPACITY
MEYERHOFF
POINT BEARING CAPACITY
MEYERHOF
PILE FOUNDATION AT MULTIPLE SAND LAYER (c = 0)
QP = Ap .qP
qP  ql l 

q    q   L

l d
ll
10 D
b
 ql d 
Where:
ql(l) : point bearing at loose sand layer (use loose
sand parameter)
ql(d) : point bearing at dense sand layer (use dense
sand parameter)
Lb = depth of penetration pile on dense sand layer
ql(l) = ql(d) = 50 . Nq* . tan  (kN/m2)
POINT BEARING CAPACITY
MEYERHOF
PILE FOUNDATION AT SATURATED CLAY LAYER (c  0)
QP = Ap (c.Nc* + q’.Nq*)
For saturated clay ( = 0), from
the curve we get:
Nq* = 0.0
Nc* = 9.0
and
QP = 9 . cu . Ap
POINT BEARING CAPACITY
VESIC
• BASE ON THEORY OF VOID/SPACE EXPANSION
• PARAMETER DESIGN IS EFFECTIVE CONDITION
QP = Ap .qP = Ap (c.Nc* + o’.N*)
WHERE:
o’ = effective stress of soil at pile point
 1  2Ko 
o' 
q'
 3 
Ko = soil lateral coefficient at rest = 1 – sin 
Nc*, N* = bearing capacity factors
Nc*   Nq * 1 cot 
3 Nq *
N * 
1  2 K o 
POINT BEARING CAPACITY
VESIC
According to Vesic’s theory
N* = f (Irr)
where
Irr = Reduced rigidity index for the soil
I rr 
Ir
1 Ir
Ir = Rigidity index
Es
Gs
Ir 

21   s c  q' tan   c  q' tan 
Es = Modulus of elasticity of soil
s = Poisson’s ratio of soil
Gs = Shear modulus of soil
 = Average volumetric strain in the plastic zone below the pile point
POINT BEARING CAPACITY
VESIC
For condition of no volume change (dense sand or saturated clay):
 = 0  Ir = Irr
For undrained conditon,  = 0
Nc* 
4
ln I rr  1    1
3
2
The value of Ir could be estimated from laboratory tests i.e.: consolidation
and triaxial
Initial estimation for several type of soil as follow:
Type of soil
Ir
Sand
70 – 150
Silt and clay (drained)
50 – 100
Clay (undrained)
100 – 200
POINT BEARING CAPACITY
JANBU
QP = Ap (c.Nc* + q’.Nq*)


2
Nq*  tan   1  tan  .e 2 'tan
Nc*  Nq * 1 cot 
2
POINT BEARING CAPACITY
BORED PILE
QP =  . Ap . Nc . Cp
Where:
 = correction factor
= 0.8 for D ≤ 1m
= 0.75 for D > 1m
Ap = section area of pile
cp = undrained cohesion at pile point
Nc = bearing capacity factor (Nc = 9)
FRICTION RESISTANCE
Qs   p.L. f
Where:
p = pile perimeter
L = incremental pile length over which p and f are taken constant
f = unit friction resistance at any depth z
FRICTION RESISTANCE
SAND
Qs   p.L. f
f  K . v '. tan 
Where:
K = effective earth coefficient
= Ko = 1 – sin  (bored pile)
= Ko to 1.4Ko (low displacement driven pile)
= Ko to 1.8Ko (high displacement driven pile)
v’ = effective vertical stress at the depth under consideration
 = soil-pile friction angle
= (0.5 – 0.8)
FRICTION RESISTANCE
CLAY
Three of the presently accepted procedures are:
1.  method
This method was proposed by Vijayvergiya and
Focht (1972), based on the assumption that the
displacement of soil caused by pile driving results
in a passive lateral pressure at any depth.
2.  method (Tomlinson)
3.  method
FRICTION RESISTANCE
CLAY -  METHOD
Qs   p.L. f av

f av    v '  2cu

Where:
v’= mean effective vertical stress
for the entire embedment length
cu = mean undrained shear strength ( = 0)
VALID ONLY FOR ONE
LAYER OF HOMOGEN
CLAY
FRICTION RESISTANCE
CLAY -  METHOD
FOR LAYERED SOIL
cu 
cu ,1.L1  cu , 2 .L2  ...
L
A1  A2  A3  ...
v' 
L
FRICTION RESISTANCE
CLAY -  METHOD
Qs   p.L. f
f   .cu
For cu  50 kN/m2
=1
FRICTION RESISTANCE
CLAY -  METHOD
Qs   p.L. f
f   . v '
Where:
v’= vertical effective stress
 = K.tanR
R = drained friction angle of remolded clay
K = earth pressure coefficient at rest
= 1 – sin R (for normally consolidated clays)
= (1 – sin R) . OCR (for overconsolidated clays)
FRICTION RESISTANCE
BORED PILE
Qs   0.45cu  p L
Where:
cu = mean undrained shear strength
p = pile perimeter
L = incremental pile length over which p is taken constant
ULTIMATE AND ALLOWABLE BEARING
CAPACITY
DRIVEN PILE
QU  QP  QS
QU
Qall 
FS
Qall 
FS= 2.5 - 4
QP QS

3 1 .5
BORED PILE
QU
Qall 
2 .5
D < 2 m and with expanded at pile point
QU
Qall 
2
no expanded at pile point
EXAMPLE
A pile with 50 cm diameter is penetrated into clay soil as shown in the
following figure:
5m
5m
NC clay
GWL
 = 18 kN/m3
cu = 30 kN/m2
R = 30o
OC clay (OCR = 2)
20 m
 = 19.6 kN/m3
cu = 100 kN/m2
R = 30o
Determine:
1. End bearing of pile
2. Friction resistance by , , and  methods
3. Allowable bearing capacity of pile (use FS = 4)