8.50 A thin layer of silt exists at a depth of 18 m below the surface of the ground. The soli above this level has an average dry unit weight of 15.1 kN/m and an average water content of 36%. The water table is almost at the ground surface level. Tests on undisturbed samples of the silt indicate the following values: c = 45 kN/m, -18, c = 36 kN/m and = 27 Estimate the shearing resistance of the silt on a horizontal plane when (a) the shear stress builds up rapidly, and (b) the shear stress builds up slowly.