MUHU A 4 m layer of sand. Of saturated unit weight 19 kN/m, overlies a 5 m layer of clay, of saturated unit weight of 20.5 kN/m. If the ground water level occurs within the sand at 2.5 m below the ground surface, determine the total and effective vertical stress acting at the centre of the clay layer. The sand above ground water level has a water content of 40% and 60% degree of saturation. (15 marks)