# A Study on the Mechanism of the Precipitation-Induced Slope Instability of Colluvium
## 1 Introduction  
With the implementation of the strategy for developing Western China, the number of large-scale hydropower stations and high-speed railways has gradually increased, and there are many colluvial slopes near these facilities. Due to its characteristics of discontinuity, complex genesis, and loose structure, a colluvial slope is very prone to instability under rainfall conditions, and the slope seriously affects the safety of infrastructure and poses a serious threat to people's lives and property [1, 2, 3, 4]. [PERSON] et al. (2008) [5] conducted a comprehensive analysis of the distribution of landslides in the upper Tiber basin, Central Italy, and concluded that the places most prone to slope failure are those with more weak rocks and disordered bedding, and the largest number of landslides is found in places with regular bedding of rocks. [PERSON] et al. (2018) [6] concluded that the rainfall in the first five days of a landslide contributes about 20% of the landslide trigger value, and that the greater the amount of rainfall that occurs in the early stage, the less rainfall required on the day the landslide is triggered. Rainfall often causes soil landslides, which are caused by a decrease in the shear strength of soilafter rainwater infiltration. Therefore, it is of great theoretical and practical significance to study the failure mode of colluvial slopes under rainfall conditions. [PERSON] et al. (2016) [7] studied the deformation and failure effect of a soil/rock mixture on straight, stepped, and undulating foundation overburden when the bedrock dip angle is 45\({}^{\circ}\) using a large shear test, which showed that, when the shape of the foundation overburden is straight, the distance between the slip surface and the foundation overburden is the closest, the angle between the slip surface and the foundation overburden is the smallest, and the time required for the pore water pressure change value and the earth pressure change value to reach the maximum value is the longest. [PERSON] et al. [8] analyzed many aspects of the control mechanism of the colluvial landslides in the Three Gorges Reservoir Region, and the results showed that the safety factor did not decrease when the inclination angle of the quasi-linear foundation overburden interface increased with equal spacing. Under multiple reservoir water cycles, with an increase in inclination, the safety factor decays exponentially. [PERSON] et al. (2023) [9] studied the failure mechanism of colluvial slopes with different amounts of stone content under rainfall conditions through model tests and found that, when the slope angle is 60\({}^{\circ}\), the slope with 30% stone content shows block sliding, the slope with 50% stone content shows multi-stage backward sliding, and the slope with 70% stone content shows collapse sliding. [PERSON] et al. (2017) [10] studied the influence of rock content on the failure process and mode of a soil/rock mixed slope, and the results showed that the slip surface was roughly distributed in a \"Y\" shape, and with the increase in stone content, the fracture surface would be deflected, on the one hand, and the failure mode would change from overall failure to multi-stage failure, on the other hand. To date, most scholars have studied reservoir water level, precipitation, and rock content [11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22], and the influence of reservoir water level on the colluvial slope has been found to increase, while research on rainfall-induced landslides mainly focuses on rainfall amount and intensity, with less research on the triggering mechanisms of landslides caused by rainfall. Some scholars have studied the effects of dense degree, silt content, water level, and other factors on pore water pressure, water content, landslide initiation, development, and failure mode through model experiments [11; 12; 13; 14].