Modelling the dynamic response of gravity retaining wall systems using OpenSees

Recent work using the OpenSees finite element software to model the response of gravity retaining walls to Ricker wavelets is presented. The behaviour of the wall system during earthquake loading is controlled by the capacity of the shallow foundation supporting the wall. OpenSees is used to verify our contention that the primary mode of failure is one of rotational deformation rather than horizontal sliding. For situations where a gravity wall is founded on a rock layer or very hard soil, the horizontal acceleration at limiting equilibrium of the wall is controlled by sliding of the wall system on the foundation layer. For all other cases, a rotational failure mechanism based on mobilising the moment capacity of the foundation controls the limiting horizontal acceleration. Simple modelling shows that the horizontal acceleration to initiate rotational failure of the foundation is less than that to initiate sliding failure. Consequently, the design criteria for gravity walls is the residual displacement generated by rotation at foundation level during the course of the earthquake. Using the realistic cyclic stress-strain models available in OpenSees we have appropriate representations of the cyclic nonlinear behaviour of the cohesionless soil backfill and cohesionless soil beneath the foundation of the wall. The finite element modelling illuminates the understanding we have obtained from simple design analyses and enables us to evaluate the accumulation of permanent displacement during the course of the input excitation.