a layer of sand 4 m thick, overlies a layer below permeability clay, 5m thick. the bulk unit weight of the sand is 16.5 KN/m^3 and its saturated unit weight is 18 KN/m^3. the saturated unit weight of the clay is 21 kN/m^3. the water table exist initially at 1m below the ground level but pumping will permanently and rapidly lower the water talbe to 3.0m below the ground level. determine the effective stress at the top, middle and bottom of the clay;
1. before pumping
2. immediately after lowering the water table
3. in the long term.
determine the change in effective stress in the clay caused by the pumping.