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

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session 17 18 pile foundations

Session 17 – 18 PILE FOUNDATIONS

Course : S0484/Foundation Engineering

Year : 2007

Version : 1/0

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
types of pile foundation9
TYPES OF PILE FOUNDATION
  • COMPOSITE PILE
  • COMBINATION OF:
  • STEEL AND CONCRETE
  • WOODEN AND CONCRETE
  • ETC
pile categories
PILE CATEGORIES

Classification of pile with respect to load transmission and functional behaviour:

  • END BEARING PILES

These piles transfer their load on to a firm stratumlocated 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.

pile categories11
PILE CATEGORIES

END BEARING PILE

pile categories12
PILE CATEGORIES

FRICTION PILE

pile categories13
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 categories14
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.

bearing capacity of pile
BEARING CAPACITY OF PILE

Two components of pile bearing capacity:

  • Point bearing capacity (QP)
  • Friction bearing capacity (QS)
point bearing capacity
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

point bearing capacity meyerhoff
POINT BEARING CAPACITYMEYERHOFF

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 meyerhof
POINT BEARING CAPACITYMEYERHOF

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)

point bearing capacity meyerhof23
POINT BEARING CAPACITYMEYERHOF

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
POINT BEARING CAPACITYVESIC
  • 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

point bearing capacity vesic25
POINT BEARING CAPACITYVESIC

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

point bearing capacity vesic26
POINT BEARING CAPACITYVESIC

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:

point bearing capacity janbu
POINT BEARING CAPACITYJANBU

QP = Ap (c.Nc* + q’.Nq*)

point bearing capacity bored pile
POINT BEARING CAPACITYBORED 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
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

friction resistance sand
FRICTION RESISTANCESAND
  • 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)

slide31
FRICTION RESISTANCECLAY
  • 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
friction resistance clay method
FRICTION RESISTANCECLAY -  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

friction resistance clay method34
FRICTION RESISTANCECLAY -  METHOD

For cu 50 kN/m2

  = 1

friction resistance clay method35
FRICTION RESISTANCECLAY -  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)

friction resistance bored pile
FRICTION RESISTANCEBORED PILE

Where:

cu = mean undrained shear strength

p = pile perimeter

L = incremental pile length over which p is taken constant

ultimate and allowable bearing capacity
ULTIMATE AND ALLOWABLE BEARING CAPACITY

DRIVEN PILE

FS= 2.5 - 4

BORED PILE

D < 2 m and with expanded at pile point

no expanded at pile point

example
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

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)
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