Bank collapse-landslide failure mechanism of typical reverse rock bank slope in Three Gorges Reservoir area

At present, most of the reverse rock slope toppling instability failure is interpreted as a progressive overall instability failure controlled by dip angle and structural plane. However, the phenomenon of leading edge collapse is common in some reservoir areas before the toppling deformation of reverse rock slope is intensified or destabilized. To further analyze the failure mechanism and disaster process of bank collapse-landslide under the constraint condition of bank collapse, this study constructed a two-dimensional model of Gongjiafang landslide in Wuxia section of Three Gorges Reservoir area to analyze the failure mechanism of bank collapse-landslide of typical reverse rock bank slope under the erosion of reservoir water level. The results show that in the process of landslide instability evolution, the bank collapse changes the slope shape, slope structure, and stress distribution. It provides important free-face conditions for the upper deformation body, which is the disaster acceleration inducement of reverse rock slope landslide failure. The main reason for the formation of landslide is that a large number of tensile cracks are produced by the cumulative bending and toppling of the anti-dip rock strata. After impoundment, the vertical and horizontal cracks are gradually produced under the influence of bank collapse and form a multi-stage sliding surface. In the process of bank collapse-landslide chain evolution, the stress and displacement of each point of the bank slope before the bank collapse did not fluctuate significantly. After the bank collapse, the stress concentration in the slope was significant with deformed slope surface, and the fracture surface was gradually penetrated. The slope toe erosion area at different depths has obvious graded slip phenomenon in the process of bank collapse-landslide evolution. Before slip, when the cumulative bending angle of the bedding plane of the rock beam at the top of the erosion area reaches 15°～23° under the extrusion of the overlying load, the unloading cracks at the trailing edge of the slope develop, and further penetrate to form a sliding surface with a depth of about 2.5～3 times deeper than that of the erosion area. The scale of landslide failure is positively correlated with the erosion depth of slope toe. The deeper the erosion depth of slope toe is, the earlier the collapse occurs, the larger the range of potential failure zone is, and the more obvious the bending slip phenomenon is in the process of rock deformation and failure. This study can provide new insight into the study on the toppling failure mechanism of the reverse rock bank slope and a theoretical basis for the prevention and control of similar bank slopes in the reservoir area.