Controlling effect of sliding zone soil on rainfall-triggered colluvial landslide in Qinling-Bashan Mountains – A typical case study

Accumulation landslide induced by rainfall is one of the most important types of geological disasters in the Qinling-Bashan Mountains, China. In recent years, nearly one hundred accumulation landslides have caused significant casualties and serious economic losses. To better understand the response mechanism of sliding zone soil to such landslides under rainfall infiltration conditions, the landslide in Zhashui County, Shaanxi Province, was taken as a typical case. The field investigation, ring shear test and creep test were carried out using sliding zone soil. Combined with the laboratory tests results, the landslide was numerically simulated and analysed. Laboratory test results show that the increase in moisture content leads to a reduction in the shear strength of the sliding zone soil, promoting slope creep and accelerating the deformation of the slope. Numerical simulation results for two typical rainfall infiltration scenarios, short-duration heavy rainfall and long-duration weak rainfall, indicate that the failure type of accumulation landslide is a creep-slide failure, and the damage degree of the heavy rainfall to the slope is greater than that of the weak rainfall. According to the results of the field investigation and numerical simulation, we find that the mechanical behaviour of the sliding zone soil controls the failure mode of the accumulation landslide in Qinling-Bashan Mountains. This kind of landslide has roughly experienced three failure stages: the early disaster-breeding stage, the interim accelerated deformation stage and the anaphase instability failure stage.