At a given location 8m thick saturated clay w = 30% G = 2.7 is underlined by Sand. The sand layer is under artesian pressure equivalent to 3m of water had it is proposed to make and excavation in clay how deep can this excavation be made before the bottom fails.

W = 30%

G = 2.7

$e_{sat}$ = W.G = 0.3*2.7 = 0.81

$\gamma_{sat} = (\frac{G+e}{1+e})\gamma_w$

$\gamma_{sat} = 19.02 KN/m^3$

For equilibrium, soil pressure = seepage pressure

$\gamma_h = \gamma_w h_w$

19.02h = 9.813

H = 1.55m depth upto which excavation can be done before bottom fail = (8-1.55) = 6.45m