Question

A site is characterized by 6 m of soft fine-grained soils (a mixture of silt and clay)overlaid by 3 m of free-draining sand. Below the fine-grained soil is free-draining fractured

bedrock. The groundwater table is located 2 m below the ground surface.Laboratory consolidation tests confirmed that the thick fine-grained layer is normally consolidated, with w = 60%, Cc = 0.45, and c, = 5 x 106 m²/min. A large embankment is placed on the surface to pre consolidate the soft layer before construction. 1. Determine the expected time for 90% average consolidation to occur 2. Choose between one of the following two options for PVD spacing, to minimize the settlement time (show all work). Extra credit (+10 points): Calculate the total settlement of the clay due to the surcharge stress, if the surcharge stress at the top of the soft layer is 100 kPa, and at the bottom of the soft layer is 30 kPa. Assume the surcharge dissipates linearly with depth.

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