A soil stratum at a site consists of a clay layer 3 m thick, overlain by a 3.5m layer of silt. The water table is 2.5 m below the surface. Due to capillary rise, silt is partly saturated above the water table and has a degree of saturation S=60%. The top 1 m layer is considered dry (S=0%). (i) Derive the following expression of the bulk unit weight in terms of specific gravity (Gs), void ratio (e), degree of saturation (S) and unit weight of water. Y = Silt: Gs=2.7, e = 0.6 (G + Se) S [5 marks] (ii) Plot the distribution of total vertical stress, porewater pressure and effective stress as functions of depth? 1+ e [12 marks] (iii) If the water table is lowered at 3.5m below the ground level, how much the effective stresses will change at the top of the clay layer? [8 marks] 1 m, S = 0% 1.5 m, S 60% Clay: Gs=2.69, e = 0.807, S = 100% Yw 1 m, S = 100% Permeable bedrock Figure Q4.1 Soil profile [Total marks: 25] 3.5 m (silt) W.L 3.0 m (clay)