## 3 Simulation of Slope Collapse Impact Load
### Longitudinal Profile Impact Simulation  
To further investigate the impact characteristics of slope collapses in the longitudinal 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 9. This section was cut longitudinally to represent the profile of the slope. The two-dimensional profile model, as illustrated in Figure 10a, 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 200 m), the right region (x = 1850 to 2400 m), and the bottom trough (y = 0 to 100 m) were modeled with large particles. Figure 8: Instability of cross-sectional slope: (**a**) monitoring of western slope impact force; (**b**) eastern slope impact force monitoring. 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 longitudinal profile simulation considered the influence of the first mining area. Figure 10b shows the state of the model after the first mining area was excavated. The first mining area was equivalent to x = 514 to 867 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. After the bottom pulling was completed, certain cracks and slippage occurred in the right-side slope (northern slope), but no instability was observed, as shown in Figure 10c. The middle loose area was designated as a subsidence area, represented by clearing the adhesive force. The overall state of the slope before instability is shown in Figure 10c, with 30 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 11. The left diagram shows the measurement circle at the left end, primarily subjected to the collapse impact of the northern slope, while the right diagram shows the measurement circle at the right end, subjected to the impact of the northern 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, similar 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 5.5 MPa, with a maximum impact stress calculated from the peak differences ranging from 0.6 to 1.8 MPa. At the back end, the peak impact stress was about 10.4 MPa, with a maximum impact stress calculated from the peak differences ranging from  
Figure 9: Schematic diagram of longitudinal section modeling. 0.8 to 2.0 MPa. The similarity in the actual maximum impact stress values, despite different peak values, further validates the rationality of the peak difference calculation method. It is worth noting that the impact stress values measured by the measurement circle at the back end were relatively high and maintained at a higher level. This is attributed to the accumulation of debris at the back end after the collapse of the northern rock mass, where the stress is no longer purely impact stress.