Physical simulation of the excavation deformation response of counter-tilt slope with rigid layers on the soft

Most of the existing researches on counter-tilt slope with rigid layers on the soft focus on the deformation evolution process of near-horizontal mudstone and shale pedestal type slopes with compression and extrusion deformation, and the excavation response of the slab-pedestal type slope with toppling deformation were seldom examined. This paper takes the slope of the Yuqu Hydropower Station in Tibet as the research object. Based on the field geological investigation, the geological structure model conforming to the actual situation of the slope is established, and the prototype slope excavation is simulated by using the physical test method. The deformation response characteristics and failure modes of counter-tilt slope with rigid layers on the soft under excavation conditions are revealed through experiments. The results show that (1) the process of deformation and failure of counter-tilt slope with rigid layers on the soft under excavation conditions is divided into three stages: (a) lower soft rock topping is intensified; (b) soft rock toppling fracture and the upper unloading hard rock along the existing crack shear; and (c) dumping soft rock slip, unloading hard rock shearing lithologic boundary points, break through the surface. The deformation failure mode is the lower soft rock toppling-upper hard rock shear-combination slip failure. (2) The large deformation caused by excavation of counter-tilt slope with rigid layers on the soft is completed in a short time, and the deformation and energy accumulation in the early stage is a long-time process. (3) During the excavation, it is necessary to avoid the “large excavation” construction of the rock mass toppling on the slope foot.