Investigating the failure mechanism of a landslide triggered by the combined effects of excavation and rainfalls through numerical approaches
摘要
On June 23, 2016, a landslide was triggered by the combination of toe excavation and rainfall infiltration in Songshuliang village, Sichuan province, China. The landslide was about 4.9 × 104 m3 and resulted in substantial damage to the surrounding buildings and roads. Field investigations and numerical analyses have been performed to explore the failure characteristics and formation mechanism of the landslide. According to field investigations, the landslide was classified as translational sliding and the interested area was divided into three parts: the traction crack area, the main sliding body area, and the collapse and accumulation area. The sliding surface passed through weathered slate layers and cut out above the retaining walls at the slope toe. A conceptual model of the landslide mechanism was constructed and the process of the landslide was divided into four stages: excavation and unloading stage, rainwater infiltration and weakening stage, translational sliding and failure stage, and collapse and accumulation stage. A series of numerical analyses using the Limit Equilibrium Method (LEM) and the finite-element-based Shear Strength Reduction Method (SSR) was performed to explore the landslide mechanism. The calculated factors of safety (FS) and critical sliding surfaces obtained from the two methods were comparatively analyzed with the post-failure observations in the field. We concluded that the toe excavation is the key factor that led the slope to a critical state by changing the slope morphology and removing the lower support of the slope, and the rainfall infiltration reduced the matric suction of rock mass and expanded the saturation area in the slope which eventually led to the occurrence of the landslide. Both LEM and SSR provide overall reasonable results in sliding surfaces matched with the field investigation. The sliding surface obtained by LEM is shallower than the observed one, while the results obtained by SSR are more convincing as they correspond to the field investigation, especially at the trailing edge of the landslide. The findings improved understanding of the failure mechanism and process of the landslide triggered by the combined effects of toe excavation and rainfall infiltration, and may provide a reference for the disaster identification of similar types of landslides.