23. Computing Seismic Displacements of Cantilever Retaining Wall Using Double Wedge Model

Case studies of failures in cantilever retaining walls during earthquakes indicate the need for better prediction of the seismic displacements of these structures. The article presents a displacement-based design methodology for these walls using a double wedge model with due consideration to sliding and rotational failure modes. The present practice is to analyze these structures as gravity retaining walls by considering a vertical plane passing through the wall-heel and the soil mass above the heel as part of the wall. However, experimental evidence suggests the formation of v-shaped rupture planes in the backfill evolving from the heel. By simulating the v-shaped mechanism, an analytical double wedge model has been developed and validated through case studies for computing seismic sliding displacements. Plane strain FE analysis was carried out for several cases of cantilever retaining wall to understand its sliding as well as rotational deformations. By comparing the results of the FE analyses and the sliding displacement predictions from double wedge model, displacement factors have been proposed as a simple design methodology to obtain seismic displacements for design purpose. The seismic behavior of walls with shear key is expected to differ from those without shear key, yet the present practice ignores this aspect due to lack of sufficient knowledge. The proposed simplified method for these walls has been extended to walls with shear key by capturing the responsible mechanism. A case study has been discussed in detail, which shows the promise of the proposed method for estimating the seismic displacement of such walls.