Investigation of rainfall-induced toe-cut slope failure mechanisms in the southeastern coastal area of China

Owing to the contradiction between the mountainous terrain and increasing population density in the southeastern coastal region of China, toe-cut slopes are widely distributed in the mountainous region for housing construction. However, the mechanisms of toe-cut slope failure remain unexplored. In this study, based on a field investigation in a sample study area in the southeastern coastal region of China, we analyzed the factors controlling the failure of toe-cut slopes in that area. The external factors include slope toe cutting and rainfall. Moreover, we carried out a series of soil tests on the residual soils of tuff and granites and found that there are also internal factors, as indicated by triaxial compression tests, whereby the shear strength of the residual tuff and granite soils significantly decreases when the soils are disturbed. Moreover, we selected the representative failure case of a terraced toe-cut slope and numerically simulated the failure process by coupling seepage analysis under rainfall using the limit equilibrium method. The simulated failure planes adequately coincide with the sliding surfaces measured in the field survey. The in situ investigation and numerical simulation results reveal that the failure of terraced toe-cut slopes under rainfall has a retrogressive mechanism. In other words, the failure starts from the lower-level stairway and then propagates to the upper levels. This study can provide the scientific basis for understanding the failure mechanism of toe-cut slopes and developing key disaster prevention technologies for the mountainous areas in the southeastern coastal region of China.