Simplifi ed approach for design of raft foundations against fault rupture. Part II: soil–structure interaction

This is the second paper of two, which describe the results of an integrated research effort to develop a four–step simplifi ed approach for design of raft foundations against dip-slip (normal and thrust) fault rupture. The fi rst two steps dealing with fault rupture propagation in the free-fi eld were presented in the companion paper. This paper develops an approximate analytical method to analyze soil–foundation–structure interaction (SFSI), involving two additional phenomena: (i) fault rupture diversion (Step 3); and (ii) modifi cation of the vertical displacement profi le (Step 4). For the fi rst phenomenon (Step 3), an approximate energy–based approach is developed to estimate the diversion of a fault rupture due to presence of a raft foundation. The normalized critical load for complete diversion is shown to be a function of soil strength, coeffi cient of earth pressure at rest, bedrock depth, and the horizontal position of the foundation relative to the outcropping fault rupture. For the second phenomenon (Step 4), a heuristic approach is proposed, which “scans” through possible equilibrium positions to detect the one that best satisfi es force and moment equilibrium. Thus, we account for the strong geometric nonlinearities that govern this interaction, such as uplifting and second order (P−Δ) effects. Comparisons with centrifuge–validated fi nite element analyses demonstrate the effi cacy of the method. Its simplicity makes possible its utilization for preliminary design.