## 3 Simulation of Slope Collapse Impact Load
### Transverse Section Impact Simulation  
To investigate the impact characteristics of slope collapses in the transverse direction, a detailed numerical simulation was conducted using the discrete element method (DEM) implemented in PFC2D. The material parameters and contact parameters used in the PFC numerical model in the article are shown in Table 1. The modeling process began with the establishment of a two-dimensional section model derived from the Rhino software 7, as shown in Figure 6. This section was cut horizontally to represent the transverse profile of the slope. Figure 5: Schematic diagram of mining area. The two-dimensional profile model, as illustrated in Figure 7a, consists of rock mass (purple) and ore body (brown) components. To enhance computational efficiency while maintaining engineering accuracy, large particles were used to simulate the rock mass in regions where detailed modeling was not critical. Specifically, the left region (x = \(-495\) to \(-50\) m), the right region (x = 1000 to 1500 m), and the bottom trough (y = 0 to 100 m) were modeled with large particles. The simulation process included several key steps: model introduction, lithology grouping, parameter assignment, excavation, and stress monitoring. The parameter assignment was tailored to reflect the engineering practice of ore drawing, with special reinforcement applied to the bottom trough to simulate the higher bonding force typically observed in these areas. Additionally, a subsidence area was introduced by setting the bonding force of the ore body in the collapse region to zero. \begin{table}
\begin{tabular}{c c c} \hline
**Parameters Types** & **PFC Parameters** & **Magnitude** \\ \hline \multirow{6}{*}{Basic parameters of particles} & Density (kg/m\({}^{3}\)) & 2600 \\  & Contact modulus (\(E_{c}/Gpa\)) & 6.3 \\  & Stiffness ratio (\(k_{n}/k_{s}\)) & 1.2 \\  & Coefficient of friction & 0.4 \\  & Small particle radius (m) & 1–1.66 \\  & Large particle radius (m) & 5–5.66 \\  & Porosity (\(P\)) & 0.16 \\  & Parallel bonding stiffness ratio & 1.5 \\  & Parallel bond modulus & 6.3 \\  & Parallel bonding internal friction & 36.8 \\  & angle (\({}^{\circ}\)) & \\  & Parallel bonding tensile & 41 \\  & strength (MPa) & 38 \\ \hline \end{tabular}
\end{table} 
Table 1: PFC parameters. Figure 6: Schematic diagram of horizontal section modeling. In this simulation, the mesoscopic parameters of the rock material were determined by referencing the existing research findings of this project. Subsequently, the displacements and contact forces of all particles were reset to zero to eliminate the influence of the initial setup on the calculation results of axial stress and strain. To enhance the accuracy of the model, an additional equilibrium calculation was conducted to minimize the interference of initial conditions on the simulation outcomes. Since the landslide in this project was triggered by underground construction works, the excavation process in the model was realized by progressively removing PFC (Particle Flow Code) particles within the excavation area. During the landslide simulation, measurement circles were placed at the bottom of the model, above the underground cavern group, to monitor the impact forces generated during the collapse of the upper rock mass and analyze the dynamic effects of the landslide instability process on the underground cavern. Figure 7: Horizontal section bottoming: (**a**) two-dimensional schematic diagram of the horizontal section; (**b**) after the bottom pulling is completed, the slope body; (**c**) slope body and monitoring measurement circle before ore instability; (**d**) slope after rock collapse. The simulation results revealed that, after the bottom pulling was completed, certain cracks appeared on the left and right slopes, but no instability occurred, as shown in Figure 7b. The middle loose area was designated as a subsidence area, represented by clearing the adhesive force, as depicted in Figure 7c.