## 3 Simulation of Slope Collapse Impact Load
### Oblique Profile Impact Simulation  
To comprehensively investigate the impact characteristics of slope collapses in the oblique direction, a detailed numerical simulation was conducted using the discrete element method (DEM) implemented in PFC2D. The modeling process began with the establishment of a two-dimensional section model derived from the Rhino software, as shown in Figure 12. This section was cut obliquely to represent the profile of the slope. The two-dimensional profile model, as illustrated in Figure 13a, 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 = 0 to 400 m), the right region (x = 1900 to 2800 m), and the bottom trough (y = 0 to 100 m) were modeled with large particles. Figure 11: The impact stress of unstable rock mass collapse on the bottom groove: (a) front section impact stress; (b) Rear end impact stress. Figure 12: Schematic diagram of oblique section modeling. 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. The oblique profile simulation considered the influence of the first mining area. Figure 13a shows the state of the model after the first mining area was excavated. The first mining area was equivalent to x = 447 to 828 m. To facilitate the simulation calculation, the first mining area was directly excavated. At this stage, the overlying rock mass exhibited significant impact stress, which was not fully accounted for in the actual situation, hence the impact stress was not considered in this phase. Figure 13: Inclined profile bottom pulling: (**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. After the bottom pulling was completed, the right-side slope (northeastern slope) did not show obvious damage, but the ore body exhibited certain cracks and slippage, as shown in Figure 13b. The overall state of the slope before instability is shown in Figure 13c, with 17 measurement circles (radius = 7.5 m) set near the bottom trough (y = 100 m) to monitor the Y-direction stress. The impact stress monitoring results are presented in Figure 14. The left diagram shows the measurement circle at the left end, primarily subjected to the collapse impact of the northeastern slope, while the right diagram shows the measurement circle at the right end, subjected to the impact of the northeastern rock mass. The impact stress analysis focused on the differences between the peaks of each curve, rather than simply taking the peak values as the final result. This approach revealed that the overall impact stress fluctuated continuously, similarly to an earthquake situation, due to the sequential caving of the slope top ore bodies rather than a single large rock mass. The peak impact stress at the front end was approximately 33 MPa, with a peak value of the fluctuation area around 6 MPa, and the maximum impact stress calculated from the peak differences ranged from 1.0 to 2.0 MPa. At the back end, the peak impact stress was about 34 MPa, with a peak value of the fluctuation area around 10 MPa, and the maximum impact stress calculated from the peak differences ranged from 1.0 to 1.8 MPa.