A layer of sand extends from ground level to a depth of 9 m and overlies a layer of clay, of very low permeability, 6 m thick. The water table is 6 m below the surface of the sand. The saturated unit weight of the sand is 19 kN/m3 and that of the clay 20 kN/ m3; the unit weight of the sand above the water table is 17 kN/m3. Over a short period of time the water table lowers by 3 m and is expected to remain permanently at this new level. Determine the effective vertical stress at depths of 8 and 12 m below ground level (a)immediately after the lowering of water table and (b)Several years after the lowering of the water table. Explain your answer for each part.

For a site, there is a layer of sand, 5.3m thick, that lies over a clay layer of 1.2m. The water table is 1.3m below the ground surface. The saturated unit weights of the sand and clay are 21.6 kN/m3 and 18.8 kN/m3, respectively. The unit weight of sand above the water table is 17.2 kN/m3. Determine the total vertical stress, porewater pressure and effective vertical stress at the bottom of each layer. Plot the values found in (a) against the depth below ground level. If the water table rises up to an elevation of 0.7 m above the ground level, what will the total vertical stress, pore water pressure and effective vertical stress at the bottom of the clay layer?