A 3.0 m thick singly drained normally consolidated clay layer has e_o = 0.89, C_c = 0.46, and c_v = 3.5 m²/year. The effective overburden pressure at the middle of the layer is 105.0 kN/m². It is proposed to build a large warehouse that is expected to impose a pressure of 50.0 kN/m² at the ground level.

a. What would the primary consolidation settlement be?

b. If the engineer proposes to preload the site with a pressure of 90.0 kN/m², how long should this surcharge be left to ensure there is no postconstruction settlement when the warehouse is built?