Formation Mechanisms of High Rock-slope Deformation Under Heavy Rainfall

A series of deformation and failure occurred at different elevations during the excavation process on the right bank slope of a dam site of a hydropower station under construction in Southeast Asia, which were mainly manifested as cracks, partial collapses, and landslides, and the slope was in a critical state of instability. Based on the actual engineering geological conditions, field geological survey and monitoring data after the excavation of the slope, the deformation characteristics of the slope were summarized and the cause mechanism of the deformation and failure was analyzed. The results show that the free surface is formed and the stress field is redistributed after slope excavation, and the rock mass rebound to the free surface, which intensifies the opening and penetration of the rock mass fissures, and provides a good channel for rainwater infiltration. The material in the F11 fault absorbs water and softens, resulting in uneven deformation, which lead to the cracks and partial landslides. The fracture accelerated its development to the deep and the rock (soil) softens rapidly as well as accumulates a large amount of compression creep due to the twice of heavy rains, the creep slip-pull crack type landslide is formed after the slip surface penetrates. This research could provide a certain degree of excavation and support for the later period.