Geotechnical Engineering

DHARM

792 GEOTECHNICAL ENGINEERING

q¢max

H

D

Scour line

H 1

BC

g¢D(K – K )pa

Fig. 19.16 Heavy well
The pressure distribution is shown in the figure. The maximum pressure at the base is
equal to γ′ (Kp – Ka) (D + Z).

Scour level

H Unscoured bed

Assumed

pressure

D distribution

H 1

z

W

g¢(D + z)(K – K )pa

q¢max

Fig. 19.17 Effect of surcharge on wells

In this case q′max is given by

q′max = (1/6)γ′(Kp – Ka).DD z

H

2

1

()+ ...(Eq. 19.33)

Safe Value of Lateral Force

For providing a margin of safety, the desired factor of safety has to be applied to the passive
earth resistance; it amounts to saying that the coefficient of mobilised passive earth resist-
ance, Kp′, is obtained by dividing the coefficient of passive earth resistance, Kp by the factor of
safety, F.S.