Geotechnical Engineering

DHARM

PILE FOUNDATIONS 683

16.7 SETTLEMENT OF PILES AND PILE GROUPS

Settlement of piles and pile groups cannot be evaluated with any degree of confidence.

16.7.1Settlement of Single Pile

Vesic has proposed an equation for computing the settlement of a single pile in cohesionless

soil, based on experiments on test piles of different sizes embedded in sands with different

density index values. These tests were conducted on driven piles, bored piles and jacked piles

(jacked piles are those that are pushed into the soil by means of the static pressure of a jack).

The equation for the settlement is

S = Sp + Sf ...(Eq. 16.49)

where S = total settlement,

Sp = settlement of pile tip, and

Sf = settlement due to deformation of pile shaft.

Further,

Sp =

CQ

Iq

wp

()1 Db

+^2 ...(Eq. 16.50)

where Qp = point load,

ID = density index of sand,

qp = unit resistance in point-bearing, and

Cw = settlement coefficient ... 0.04 for driven piles,

0.18 for bored piles, and

0.05 for jacked piles.

Sf = (Qp + αQf)

L

AE

...(Eq. 16.51)

where, Qf = Friction load,

L = Length of pile,

A = Area of cross-section of pile,

E = Modulus of elasticity of pile material, and

α = Coefficient which depends on the distribution of skin friction along the shaft and is

usually taken as 0.6.

Settlement of a single pile in clay is more difficult to evaluate. An assumption is re-

quired to be made regarding the level to which the load is transferred. If the pile penetrates

homogeneous clay, the load may be taken to be transmitted to a depth of

3
2 the embedded
length of the pile from the surface. Concepts of stress distribution in soil (Boussinesq’s, for
example), coupled with the settlement due to consolidation will be used. If the pile penetrates
a weak stratum and is embedded into a firm stratum, the load may be taken to be transmitted

to a level at a depth of

2

3

of the depth of embedment into the firm stratum from the top of the

firm stratum.