Seismic design of bridge structures is based on a displacement-performance philosophy. Full-scaled field experiments, observations from the major seismic events and post-earthquake studies have indicated that the bridge abutment-backfill exhibits strength and stiffness degradation. Hence it is important to incorporate the degradation of the abutment-backfill in the bridge global model in relation to it’s the seismic response and performance. This article’s focus is on the development of stiffness degradation (nonlinear load deformation curve) for the earth pressure behind bridge abutments. This problem has recently been studied experimentally at several universities and research institutes in the USA and good-quality, large-scale test results are available. Backcalculations of the test results using 3DTunnel and 3DFoundations are shown herein. The Hardening Soil Model has been used to simulate the nonlinear abutmentbackfill force-deformation relationship from some of these tests. The Plaxis results are in good agreement with the experimental results and the simulations provide valuable information on the soil behavior and the soil parameters. It is concluded that Plaxis is an extremely valuable tool for the practicing bridge engineer in capturing realistic nonlinear soil-abutment-structure interaction curves.