Insights into Seismic Deformation Patterns for Shallow and Deep Sliding Masses Using Finite Element Analysis

Earthquake-induced slope displacements are typically estimated using a sliding block analysis. Sliding block approaches, for both rigid and flexible sliding masses, have been shown to roughly capture the observed seismic performance of slopes during previous earthquakes. However, these approaches incorporate simplifying assumptions that do not represent the full dynamic response of a slope. Two-dimensional (2D), nonlinear, total stress finite-element analyses were performed to identify the seismic deformation patterns for shallow (friction-dominated) and deeper (cohesion-dominated) critical sliding masses. The numerical parametric analyses consisted of four models with soil stiffness and strength parameters selected to isolate the impact of the slope seismic resistance (i.e., k_y) and the depth of the slip surface on seismic slope deformation patterns. Each model was analyzed in the context of how the ground motion intensity (in terms of peak ground velocity, PGV) affects the maximum permanent displacement along the surface of the slope, the profiles of permanent displacement and shear strain, and the stress-strain behavior at different depths. The results indicate that for the same k_y and same T_slope, the displacement is significantly affected by the depth of the critical sliding mass due to the distribution of static shear stress and soil’s shear strength along with the slope height. For the conditions considered, at small k_y the deeper sliding masses experience larger displacements due to the presence of localized straining at depth. Their slope displacements are about 1.2–2 times greater than their counterparts with shallow sliding surfaces, particularly when the PGV is greater than 20 cm/s. At large k_y, shallow sliding masses experience more distributed straining across the entire sliding mass depth (and hence slope displacements), leading to displacements about 1.25–2 times larger than the deep sliding mass models. These insights point to the importance of considering more advanced numerical simulations (as opposed to traditional sliding block analysis) when quantifying the seismic performance of a slope.