Development characteristics and formation mechanism of the medium-dip bedding slopes：A case study of the landslide on the left bank of Tuodan reservoir dam

Controlled by the slope structure and petrophysic properties, there are many engineering geological problems such as deformation, collapse in the medium-dip bedding slopes, and landslides, which often induce large-scale geological disasters. The potential sliding surface of this slope type does not directly expose on the surface, and it generally has the characteristics of complicated deformation mechanism, high concealment and great harm, which is the focus in the field of landslides research. The left bank of Tuodan reservoir dam is an ancient landslide. During the expansion and excavation of the reservoir, the ancient landslide was revived. Based on the analysis of the engineering geological conditions of the deformation body, combined with the results of geological survey and deformation monitoring, the deformation characteristics and formation mechanism are studied. The research results show that: ①The rock stratum dip has the characteristics of “steep upward and gentle downward” in ancient landslide of left bank. There is a shear fracture zone in the anti-inclined slope at the bottom of the landslide body, and the rock body of the slide bed is arch-bend.; ②The ancient landslide is a bedrock bedding landslide, and its sliding mode is “slip(bending)-shear” type. The deformation and failure process includes three stages, slipping shear-out stage and disturbance deformation stage; ③After the deformation and failure of the slope, it is more likely to slide again along the chair-shaped soft layer. The key to landslide control is to protect the lower deformation area.