A trench is proposed for utilities along a very long slope that consists of two soils. The top soil is a fissured saturated clay (γsat = 20 kN/m3, ∅'cs = 25°, (su)cs 5 20 kPa) and the soil below it is a thick, heavily over consolidated, stiff saturated clay with (su)p 5 80 kPa (Figure P10.24). The groundwater level is 8 m below the ground surface. One of the potential failure mechanisms consists of the top clay sliding as a rigid block at the interface. Consider a 1-m length of slope. Calculate the factor of safety (failure shear stress/shear stress imposed) of the slope for (a) short-term and (b) long-term conditions. Assume that the friction angle at the interface of the two soils is 25°.
