9. Evaluation of the Roles of Reservoir Impoundment and Rainfall for the Qianjiangping Landslide in Zigui County, Three Gorges Area

The Qianjiangping landslide occurred following the first impoundment of the Three Gorges reservoir and a prolonged rainfall. To evaluate the quantitative effects of the reservoir impoundment and rainfall on the landslide, a sensitive analysis was performed with particular consideration to the landslide’s unique characteristics and the seven parameters susceptible to the interactions between the landslide’s materials and water from the two sources. These parameters include unit weight of the landslide’s material, groundwater level above the slip zone, shear strength components of the upper and lower sections of the landslide’s slip zone, and uplift pressure of the reservoir water. Results of this study show that the factor of safety (FS) of the landslide was the most sensitive to the cohesion of shear strength of the slip zone’s lower section, and the least sensitive to groundwater level above the slip zone. It is found that the effect of shear strength reduction of the slip zone’s lower section was the most crucial in the landslide’s initiation. The landslide resulted from the combined influences of the reservoir impoundment and rainfall. The role of the reservoir impoundment in the landslide was dominant with a contribution percentage about 61.3%, whereas rainfall may have been the factor triggering the landslide.