Design a shallow foundation (its shape, dimension and placement) in the soil site shown below. The sand above the water table has a unit weight of 17 kN/m and below the water table its saturated unit weight is 19 kN/m, its angle of friction is = 25. The clay layer has a saturated unit weight of 20 kN/m, its cohesion is 20 kN/m2 and angle of friction is 30. The Poisson’s ratio and modulus of elasticity for the sand are 0.25 and 20 MN/m, respectively; for the clay, they are 0.3 and 30 MN/m. The clay is an overly consolidated clay with a compression index Cc = 0.26 and its recompression index can be estimated as Cr = 0.2Cc, its pre-consolidation stress is 160 kPa and its original void ratio is 1.2. The foundation is supposed to support a dead load of 500 kN and a live load of 400 kN. 1 m V 1 m sand 4 m clay Rock Use the Load Resistance Factor Design (LRFD) method for strength requirement, based on AASHTO’s LRFD recommendations. The service requirement is that the allowable settlement should not exceed 50 mm.
