Seismic effective-stress analysis of caisson quay walls: Application to Kobe

Abstract

Deformation-based seismic design of gravity quay-walls requires realistic computation of residual deformations. This article presents an effective-stress analysis method, which is based on an elasto-plastic constitutive model formulated into a finite-difference algorithm. The model is applicable to cohesionless soils, for a wide range of relative densities and confining pressures. The formulation is applied first to re-analyze one of the failed caisson-type quay-walls of Rokko Island during the 1995 Kobe (Hyogoken-nambu) earthquake (Case 1). Subsequently, it is applied to analyse three closely related case studies of quay-walls, subjected to the same earthquake excitation, to demonstrate the effects of ground improvement on the wall performance. Case 2 considers a quay-wall in which both the foundation and backfill consist of improved, non-liquefiable soils. Case 3 considers a quay-wall in which the backfill soil remains liquefiable, whereas the foundation soil has been improved. Finally, in Case 4 the foundation soil is liquefiable, and the backfill soil improved. The results are consistent with both field observations and earlier independent computer simulations by lai et al. 1998 which were based on the finite-element method and a different constitutive model.