A deformation-based method that can be used for the analysis of the seismic response and for the design of waterfront retaining structures is developed. The study is focused on the behavior of gravity caisson-type quay walls. The key element for the success of the method lies on the selection of an appropriate constitutive model that can describe adequately the monotonic and cyclic undrained behavior of soil subjected to arbitrary stress paths. To this end, an existing generalized plasticity model, developed by Pastor et al. (1990), was examined and modified in order to improve its performance. Comparisons with a centrifuge model study and a case history from the recent 1995 Kobe earthquake on gravity quay walls are used for the evaluation of the new method of analysis, based on the modified generalized plasticity model. Particular emphasis is given to the undrained behavior of the foundation and backfill sand, and its effect on the deformational mechanism and damage of the quay walls.