Extended Newmark method to assess stability of slope under bidirectional seismic loading

The paper concerns the dynamic behavior of a simple slope model subjected to simultaneous horizontal and vertical excitations. The proposed method is based on Newmark?s sliding block concept, however, four new features are introduced. The most important assumption is that the normal component of dynamic excitations affects the resisting force both before and after the initiation of the relative slope motion, making it time dependent. The proposed formula and solution method is validated by experiments conducted on the shaking table and the bidirectional oscillatory device. The block displacement and acceleration time-histories are measured and analyzed. Experiments results conducted for bidirectional cyclic motion showed that the influence of vertical acceleration on the stability of the slope can be both negligible and significant (up to 57%). The numerical tests results, performed for thirty-five European seismic records, showed the underestimation of permanent displacement can reach up to 19% if the vertical excitation is neglected.