Vertical Acceleration Effect on Slope Stability: A Simplified Coupled Insight

Abstract The paper focuses on the effect of the vertical ground acceleration component on slope stability. The proposed stability method is based on Newmark’s sliding block concept, which provides an intuitive indicator of slope stability. Contrary to the original Newmark method, both components of excitations, tangent and normal to the slip plane, are considered in force equilibrium. In the paper, the extended Newmark method is coupled with dynamic response obtained using the FEM and a direct time-integration scheme. Coupling the simple stability approach with the stress distribution history eliminates uncertainty in determining the intensity of the dynamic load acting on the sliding block. In the coupled method, the equilibrium of the sliding and resisting forces is considered along the discretized slip plane. When the limit equilibrium is reached, the relative movement of the block begins, and the permanent displacement of a sliding mass is accumulated. The influence of excitation components on permanent displacement is examined using a uniform steep slope as an example. The presented results indicate that shallow deformation mechanisms are more strongly affected by inertial forces than deeper ones. In the analyzed cases, the peak average acceleration for the shallow mechanism was between 1.2 and 3.0 times that for the deep mechanism. Furthermore, the effect of vertical acceleration on permanent displacements is notably more significant in shallow failure modes. It is shown that the permanent displacement obtained by the original Newmark’s method can be 74.3% lower than that obtained by the extended Newmark’s method. The impact of vertical acceleration itself can reach 24.6%.