NUMERICAL MODELLING OF SEISMIC RESPONSE OF CANTILEVER EARTH-RETAINING STRUCTURES

In current engineering practice the seismic design of earth retaining structures is usually carried out using empirical methods. Dynamic earth pressures are calculated assuming seismic coefficients acting in the horizontal and vertical directions calculated with either the Mononobe-Okabe or the Wood method depending on the anticipated movement that the structure will undergo when subjected to earthquake loading. This paper illustrates the results of a research investigation aimed to assess the appropriateness of using the Mononobe-Okabe method for determining the dynamically-induced lateral earth pressures on the stem portion of concrete, flexible cantilever retaining walls sustaining a granular backfill. A series of non-linear dynamic finite element analyses have been performed using the computer program DIANA (DIsplacement ANAlyzer). The analyses included a static-phase of stress initialization caused by placement of soil and incremental construction of the wall followed by dynamic analyses. Soil response was simulated using an elasto-plastic, Mohr-Coulomb constitutive model. The influence of variables such as wall stiffness and strength parameters of the backfill were investigated through a parametric study. Special attention was given to the selection of seismic input in order to represent realistic ground motion scenarios corresponding to different levels of severity. Dynamic earth pressures obtained from numerical simulations were compared with those determined using pseudo-static approaches through a series of benchmark tests. Co-seismic and post-seismic displacements of the wall were also calculated using simplified pseudo-dynamic methods. Reliability of the results obtained with DIANA was assessed through a validation test performed using the finite difference-based program FLAC (Fast Lagrangian Analysis of Continua).