Failure Modes and Mechanisms of Shallow Debris Landslides Using an Artificial Rainfall Model Experiment on Qin-ba Mountain

Abstract

Landslides triggered by rainfall are a major multiple geological hazard on Qin-ba Mountain. Debris landslides in the shallow layer make up a large proportion of all landslides. A flume experiment was conducted to successfully initiate shallow debris landslides using artificial rainfall in Zhouzhi County, Qin-ba Mountain. The results confirmed a strong correlation between the deformation of the slope and pore-water pressure and moisture content. Slope deformation and failure were observed, and a possible mechanism was interpreted based on the experimental results. The primary effects of rainfall on shallow debris landslides on Qin-ba Mountain are the generation of a seepage force and a decrease in the effective stress of the sliding surface as a result of increasing pore-water pressure. The effect of rainfall on the shear strength parameters is inconspicuous, which might be attributed to the relatively high saturation of debris soils under natural conditions. The failure type in Test 1 is considered to be a progressive failure, which is a typical failure mode for homogeneous shallow debris slopes on Qin-ba Mountain, particularly for slopes exposed to artificial excavation. The deformation in Test 2 with higher density, merely taking the form of surface erosion, usually occurs in the regions with the least artificial disturbance. The two deformation types can be primarily attributed to differences in the soil density; the higher density reflected the smaller number and size of inside pores and led to lower soil permeability, which further influenced the distribution of the pore-water pressure, direction of seepage force, and slope deformation. Therefore, higher soil density changed by compaction is beneficial for the stability of shallow debris slopes on Qin-ba Mountain, even with high pore-water pressure. In subsequent work, a series of experiments with various densities should be conducted to explore the dividing point between the two deformation modes, and in addition, tests with larger slope gradients should also be considered.