# A Theory of Slope Shear Scouring and the Failure Mechanism of PFC3D on a Gangue Slope
## 1 Introduction
[18] carried out an experimental study on the destabilization mechanism of rolling-stone landslides under rainy conditions and derived a simple-step stability calculation formula for rolling-stone slopes under the conditions of rainfall infiltration. [PERSON] et al. [19] analyzed the non-orthogonal infiltration regularity of unsaturated sandy soils with the rainfall intensity, slope angle, and porosity ratio. [PERSON] et al. [20] calculated one-dimensional seepage and the two-dimensional seepage process of rainy slopes using the finite element method. [PERSON] et al. [21] proposed a study on the three-dimensional (3D) undrained slopes in anisotropic and heterogenous clay using advanced upper and lower bounds finite element limit analysis (FELA). [PERSON] [22] presents new plasticity solutions for the undrained stability of unsupported conical slopes in two-layered clays using an axisymmetric finite element limit analysis. [PERSON] et al. [23] analyzed climate change and landslides in Taiwan and put forward the combination of landslide warning models in the cumulative rainfall duration diagram with a rainfall intensity classification and an average rainfall intensity duration diagram with a rainfall intensity classification. The mechanical analysis of rocks is also particularly important. Many scholars have conducted studies on the shear behavior of rocks and slopes, including simulations [24, 25, 26, 27]. In addition, other scholars have focused on the characteristics of slope scouring [28; 29], the mechanisms of gully erosion [30; 31], and the impact factors of scouring [32; 33; 34; 35]. Many scholars are committed to using continuous-medium methods (FEM, FDM, PFEM) in their research, but these methods have some drawbacks. In the process of calculation, it is often difficult to calculate convergence when plastic problems are encountered. In addition, continuous-medium calculation methods cannot effectively handle, calculate, or simulate dynamic movement and large deformation. The advantage of the PFC (particle flow code) is that it can simulate the material movement and stress transfer inside the soil body in a relatively simple way, as well as the deformation, expansion, and extension of the rock and soil body. The location and number of particles produced during sample failure, stress and strain in the sample, the shape of the soil deformation, and the strength of the model can be monitored. In this way, the mechanical testing of simulated soil material and model tests can be observed on the micro and macro scales. At the same time, the discrete element PFC method combines seepage with soil mass, considers the interaction between water and soil, and can dynamically evolve the large deformation characteristics of soil mass under the action of rainfall, as well as enabling micro-dynamic analysis. Therefore, the non-continuous discrete-element PFC is the most suitable method for determining the scouring mechanisms of gangue slopes. However, most scholars have not applied discrete-element technology to study the development and evolution of gullies, nor have they utilized a set of relatively mature shear-scouring theories. The fluid-solid coupling technology of the discrete element is not combined with this theory. Therefore, this research method is unique in the field of gangue slope studies. In this paper, we thus continue to optimize scouring the shear failure theory [36] and aim to explore the scouring failure mechanisms of gangue slopes by combining the PFC3D-improved fluid-solid coupling model.