The computer program DFSAP provides direct assessment of the three-dimensional/rotational spring stiffnesses of an isolated short, intermediate or long pile/shaft or similar stiffness of a pile/shaft group with our without cap. Accordingly, the bridge engineer will be able to assess the various springs of the foundation stiffness matrix with disregard for the complexity of the soil profile, the type and arrangement of piles/shafts, and nonlinear material behavior. Soil liquifaction and the associated induced pore water pressures are considered in the assessed foundation stiffness. Lateral spreading of the soil is an important phenomenon and is also handled by the DFSAP program. The DFSAP program is based on the well established
concepts of the Strain Wedge model for laterally loaded piles/shafts and pile groups.