Example Problem 6.13 A pile that has a diameter of 1.0 ft (0.3 m) and that is 20 ft (6 m)
long is driven into a uniform clay deposit that has a medium consistency. The clay has a uniform
undrained shear strength s
u
=750 psf (36 kPa) and a total unit weight =125 pcf (20 kN/m3
).
Assume that only the upper 5 ft (1.5 m) of the pile deflects sufficiently to develop passive pressure. Determine the amount of lateral deflection of the pile head assuming the values in Table
11.1 are applicable. Also determine the passive resistance of this upper 5 ft (1.5 m) of soil.
Solution From Table 11.1, for clay having a medium consistency, use a value of horizontal
displacement divided by height of pile subjected to passive resistance of
1
/
2
(0.02 +0.04) =0.03
Horizontal deflection of pile head for passive resistance in the upper 5 ft (1.5 m) of soil is
(0.03)(60 in.) =1.8 in. (4.6 cm)
To determine passive resistance, use Eq. (6.29):
P
p
=1
/
2
g
tDH2
+2s
uDH=1
/
2
(125)(1.0)(5)
2
+(2)(750)(1)(5) =9,100 lb (40 kN)