Analysis of seismic dynamic thrust for cantilever retaining walls as affected by sloped backfill and surcharge: from finite element modeling to simplified sliding surface geometry

Abstract This study develops a generalized analytical formulation for estimating seismic thrust on cantilever retaining walls supporting cohesive sloped backfills under surcharge. Traditional pseudo-static methods often overlook the stabilizing role of cohesion and fail to represent complex failure mechanisms observed under seismic loading. To address these limitations, a series of two-dimensional finite element simulations was carried out using PLAXIS 2D to investigate the evolution of failure surfaces under seismic excitation. The proposed formulation incorporates the effects of soil cohesion (up to 30 kPa), backfill slope inclinations (up to 15°), and uniform surcharge loads (up to 30 kPa). Simulation results show that increasing cohesion reduces the extent of failure zones by up to 40%, while the inclination of these surfaces remains nearly constant. The evolution of shear strain during seismic loading shows that cohesive backfills experience significantly lower deformation levels, with peak strains remaining below 85 × 10⁻ 3 (8.5%), compared to 200 × 10⁻ 3 (20%) in non-cohesive soils. The formulation remains valid for moderate cohesion levels (up to 20 kPa) and horizontal seismic coefficients up to kh​ = 0.6. By integrating numerical insights into a simplified analytical model, this method offers a practical and robust tool for seismic design of retaining structures under complex soil conditions.