Seismic Performance of Cantilever Retaining Walls with Clayey Backfills

Abstract

Current engineering design methods for evaluating the seismic lateral earth pressures of retaining walls are based on limit equilibrium Mononobe-Okabe method. In limit equilibrium method, the effect of dynamic loading is introduced to the soil wedge behind the retaining wall as lateral and vertical inertia forces. The two most important simplifications of these methods are application of pseudo-static solution procedure for a fully dynamic problem and assumption of cohesionless backfill material. In this investigation, a full dynamic numerical modeling on a retaining wall with low frictional angle backfill material is conducted to evaluate the seismic performance of retaining wall and lateral earth pressure variation during the earthquake. A 6-meter high cantilever wall with a base width of 4 m and thickness of 0.5 m is represented by structural element. The concrete wall was assumed to perform elastically and the Mohr-Coulomb constitutive model was selected for soil material. The interaction between concrete wall and soil was modeled by using elasto-plastic bilinear model to account for shear sliding and normal separation of wall and soil. The performance of the retaining wall was analyzed under three distinct earthquakes. The lateral earth pressure distribution along the wall height was evaluated during the earthquakes and was compared to static earth pressure. Furthermore, a set of dynamic analysis were conducted with normalized peak ground acceleration, PGA, of the earthquakes. The dynamic lateral earth pressure coefficients along the stem, middle and heel of the wall during the earthquake were analyzed for various horizontal PGAs induced by earthquakes. Consequently, the lateral earth pressure coefficients along the wall were compared to those concluded by Mononobe-Okabe method. According to the results, in low frictional angle soil backfills that have some cohesion, the lateral earth pressures are overestimated by Mononobe-Okabe method.