Question

A 50-ft 2x4 drilled shaft group was installed in subsoil conditions, ( 15-ft sand overlain a 25-ft medium clay, which is underlain by a thick over-consolidated clay shale). The drilled shafts are tipped in clay shale at 50-ft depth to support a heavy highway bridge pier. The shaft diameter is 36 inches and placed at a center-center spacing of 6 feet. The strength properties of soils are 37^ofriction angle for the sand with unit weight of 125 pcf, undrained shear strength of medium clay is 1,800 psf with unit weight of 130 pcf and the undrained shear strength of the heavily over-consolidated clay shale 3,000 psf with the unit weight of 140 pcf. Compute the design bearing capacity of the drilled shaft group with the factor of safety 2.5.

Note: When you suspect some missing information, please make reasonable assumption(s) and proceed with your solution. Clearly show why the assumption(s) is needed.

Answer 1