1. Session 17 – 18 PILE FOUNDATIONS
Course : S0484/Foundation Engineering
Year : 2007
Version : 1/0
Session 17 – 18 PILE FOUNDATIONS

2. 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

3. INTRODUCTION

4. TYPES OF PILE FOUNDATION
STEEL PILE

5. TYPES OF PILE FOUNDATION
CONCRETE PILE

6. TYPES OF PILE FOUNDATION
CONCRETE PILE

7. TYPES OF PILE FOUNDATION

8. TYPES OF PILE FOUNDATION
WOODEN PILE

9. TYPES OF PILE FOUNDATION
COMPOSITE PILE
COMBINATION OF:
STEEL AND CONCRETE
WOODEN AND CONCRETE
ETC

10. PILE CATEGORIES END BEARING PILES
Classification of pile with respect to load transmission and functional behaviour:
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
FRICTION PILES
Carrying capacity is derived mainly from the adhesion or friction of the soil in contact with the shaft of the pile
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.

11. PILE CATEGORIES
END BEARING PILE

12. PILE CATEGORIES
FRICTION PILE

13. 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.

14. Classification of pile with respect to effect on the soil Bored Pile
PILE CATEGORIES
Classification of pile with respect to effect on the soil
Bored Pile
Bored piles(Replacement piles) are generally considered to be non-displacement 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.

15. PILE CATEGORIES

16. DETERMINATION OF PILE LENGTH

17. BEARING CAPACITY OF PILE
Two components of pile bearing capacity:
Point bearing capacity (QP)
Friction bearing capacity (QS)

18. BEARING CAPACITY OF PILE

19. 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
Deep Foundation
Where D is pile diameter, the 3rd part of equation is neglected due to its small contribution
qu = qP = c.Nc* + q.Nq* + .D.N*
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

20. 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)

21. POINT BEARING CAPACITY MEYERHOFF

22. POINT BEARING CAPACITY MEYERHOF
PILE FOUNDATION AT MULTIPLE SAND LAYER (c = 0)
QP = Ap .qP
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)

23. 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

24. 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
Ko = soil lateral coefficient at rest = 1 – sin 
Nc*, N* = bearing capacity factors

25. POINT BEARING CAPACITY VESIC
According to Vesic’s theory
N* = f (Irr)
where
Irr = Reduced rigidity index for the soil
Ir = Rigidity index
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

26. POINT BEARING CAPACITY VESIC
For condition of no volume change (dense sand or saturated clay):
 = 0  Ir = Irr
For undrained conditon,  = 0
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

27. POINT BEARING CAPACITY JANBU
QP = Ap (c.Nc* + q’.Nq*)

28. 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)

29. FRICTION RESISTANCE Where: p = pile perimeter
L = incremental pile length over which p and f are taken constant
f = unit friction resistance at any depth z

30. FRICTION RESISTANCE SAND
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)

31. FRICTION RESISTANCE CLAY
Three of the presently accepted procedures are:
 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.
 method (Tomlinson)
 method

32. FRICTION RESISTANCE CLAY -  METHOD
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

33. FRICTION RESISTANCE CLAY -  METHOD
FOR LAYERED SOIL

34. FRICTION RESISTANCE CLAY -  METHOD
For cu  50 kN/m2
  = 1

35. FRICTION RESISTANCE CLAY -  METHOD
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)

36. FRICTION RESISTANCE BORED PILE
Where:
cu = mean undrained shear strength
p = pile perimeter
L = incremental pile length over which p is taken constant

37. ULTIMATE AND ALLOWABLE BEARING CAPACITY
DRIVEN PILE
FS=
BORED PILE
D < 2 m and with expanded at pile point
no expanded at pile point

38. EXAMPLE
A pile with 50 cm diameter is penetrated into clay soil as shown in the following figure:
NC clay
 = 18 kN/m3
cu = 30 kN/m2
R = 30o
5 m
20 m
GWL
OC clay (OCR = 2)
 = 19.6 kN/m3
cu = 100 kN/m2
R = 30o
Determine:
End bearing of pile
Friction resistance by , , and  methods
Allowable bearing capacity of pile (use FS = 4)