Rock toppling failure mode influenced by local response to earthquakes

Abstract

Earthquake waves influence rock toppling stability, and the effects of local earthquake propagation and topographic also affect slope deformation. Detailed engineering geology conditions of slopes are obtained and a geomechanical characterization of rock topplings is performed. To study the input earthquake waves and slope interactions, a dynamic analysis is performed using the UDEC 4.0 discrete element method (DEM) numerical code under viscoplastic conditions. The earthquake signals are representative of different peak ground acceleration, Arias intensities, and frequencies, and are used in the study of different rock topplings with different height, slope angle, and strata dip angle. The derived outputs are processed for the earthquake propagation study and to assess the induced deformation mechanisms in terms of resulting displacements, plastic zone features, and deformation mode. The results prove that an interaction exists between stratigraphic and topographic effects on earthquake wave propagation, and that these effects cannot be assessed independently. The obtained results describe the effect of topography and geological settings in rock topplings, amplifying or de-amplifying earthquake ground motion, and demonstrate that the tensile state dominates at the slope surface but evolves with depth. A shear state dominates at the toe or in the deep part of rock topplings. The rock toppling deformation mode may develop into a composite of tension fractures at the crest and sliding at depth. Compared with the static scenario, under earthquake load, tensile deformation evolves over a larger area at the crest and develops a shear zone at the toe and in the substrata. The necessary earthquake-induced toppling conditions are discussed, and the UDEC 4.0 DEM method and conventional pseudostatic approach are compared. This study shows there are a broader range of deformations inside the slope.