Page 41 - Unit2.docx

influence on the accuracy of predictions of changes in soil type and other factors
such as the time delay before load testing.

(Fig 4-2II) the load settlement response is composed of two separate
components, the linear elastic shaft friction R and non-linear base resistance
s
R . The concept of the separate evaluation of shaft friction and base resistance
b
forms the bases of "static or soil mechanics" calculation of pile carrying capacity.
The basic equations to be used for this are written as:

Q = Q + Q - W
s
b
p
or R = R + R -
c
s
b
W
p

R = R + W p
t
s

Where: Q = R = the ultimate compression resistance of the pile
c

Q = R = base resistance
b
b

Q = R = shaft resistance
s
s

W = weight of the pile
p
© It's Engg. Life
R = tensile resistance of pile
t

In terms of soil mechanics theory, the ultimate skin friction on the pile shaft is
related to the horizontal effective stress acting on the shaft and the effective
remoulded angle of friction between the pile and the clay and the ultimate
shaft resistance R can be evaluated by integration of the pile-soil shear
s
strength τ over the surface area of the shaft:
a

τ = C + σ tanφ
n⋅
a
a
a

Where: σ n = Ks⋅ σ v (refer geotechnical notes)

a
v ⋅
a
a
S
∴ τ = C + K ⋅ σ tanφ

and

where: p = pile perimeter

L = pile length

φ = angle of friction between pile and

soil K = coefficient of lateral pressure
s