Analysis of Failure Mechanism of Medium-Steep Bedding Rock Slopes under Seismic Action

Medium-steep bedding rock slopes (MBRSs) are generally considered relatively stable, because the dip angle of the rock layers (45–55°) is larger than the slope angle (40–45°). However, the stability of MBRSs was significantly impacted during the 1933 Diexi earthquake, leading to slope instability. Field investigations revealed that no continuous sliding surface was recognized in the failure slopes. Instead, the source areas of landslides present a “reverse steps” feature, where the step surfaces are perpendicular to the bedding surface, and their normal directions point towards the crest of the slopes. These orientations of “reverse steps” differ significantly from those of steps formed under static conditions, which makes it difficult to explain the phenomenon using traditional failure mechanism of the slope. Therefore, a large-scale shaking table test was conducted to replicate the deformation and failure processes of MBRSs under seismic action. The test revealed the elevation amplification effect, where the amplification factors of the acceleration increased with increasing elevation. As the amplitude of the input seismic wave increased, the acceleration amplification factor initially rose and subsequently decreased with the increase in the shear strain of the rock mass. The dynamic response of the slope under Z-direction seismic waves is stronger than that under X-direction seismic waves. The deformation and failure were mainly concentrated in the upper part of the slope, which was in good agreement with the field observations. Based on these findings, the deformation and failure mechanism of MBRSs was analyzed by considering both the spatial relationship between the seismogenic fault and the slope, and the propagation characteristics of seismic waves along the slope. The seismic failure mode of MBRSs in the study area was characterized as flexural–tensile failure. This work can provide a reference for post-earthquake disaster investigation, as well as disaster prevention and mitigation, in seismically active regions.