A 3 meter thick fill was placed over a 9 meter thick compressible clay. Underlying the clay layer is a very hard impermeable clay. The groundwater table is located on top of the compressible clay. A circular tank 9 meters in diameter transfers a surface contact stress of 45 kPa.  Assume for this problem that the settlement of the fill and the very hard clay is small compared to the settlement of the compressible clay.  a) Calculate the initial void ratio and saturated density of the compressible clay. b) Divide the compressible layer into two sublayers of equal thickness.  The preconsolidation pressure is 100 kPa for the upper sublayer and 160 kPa for the lower sublayer.  Calculate the following at the center of each sublayer: the increase in vertical stress caused by the tank underneath its center, and the consolidation setttlement due to the combined effect of the tank and weight of fill. c) How long will it take for 0.18 meters of settlement to occur? d) After 3.6 years, what percent consolidation has occurred at the middle of the compressible clay?