You have been selected to assist the structural engineer for a bridge replacement project.  Your task is to design the size of the footing for an interior bridge pier, based on the allowable stress design method.  A soil test boring was drilled at the location of the bridge pier.  The soil test boring log has shown that the soil is fairly uniform at the pier location and consists of a layer of clay overlying a three-layer system of silty sand, well graded sand, and uniform sand.  Detailed information about each layer is given in Fig. 1.  Groundwater table was encountered at the depth of 9.1 meters during subsurface exploration, but seasonal changes may raise the water table to a depth of 7.5 meters below ground surface.