Oedometer Test

An office block with an adjacent underground car park is to be built at a site where a 6m-thick layer of saturated clay (g = 20 kN/m3) is overlain by 4m of sands and gravels (g = 18 kN/m3) and underlain by permeable fractured bedrock. The water table is at the top of the clay layer, and pore water pressures are hydrostatic below this depth. The foundation for the office block will exert a uniform surcharge of 75 kPa at the surface of the sands and gravels. The foundation for the car park will exert a surcharge of 30 kPa at the surface of the clay, following removal by excavation of the sands and gravels.

Calculate the initial and final vertical total stress, pore water pressure and vertical effective stress, at the mid-depth of the clay layer, (a) beneath the office block; and (b) beneath the car park. Take the unit weight of water as 9.81kN/m3.

Initially sv = 132 kPa; u = 29.4 kPa; s'v = 102.6 kPa. Finally beneath the office block sv = 212 kPa; u = 29.4 kPa; s'v = 177.6 kPa. Finally beneath the car park sv = 90 kPa; u = 29.4 kPa; s'v = 60.6 kPa