## 7 Overall Large Block Collapse Impact Effect  
For the uncovered bottom structure, an impact load of 192 kN was applied (Figure 22). The load-displacement curve (Figure 22a) showed a significant increase in deformation, with a notable stress drop at the peak load point, indicating localized failure. The earth pressure gauges recorded varying peak loads at different locations, with the highest force value in channel 2 and the lowest in channel 5. The mechanical response revealed that the bottom structure experienced significant strain accumulation and localized damage, particularly in the form of fractured pillars between the ore accumulation troughs (Figure 23). Figure 21: Load–displacement curve and soil pressure–normalized time curve of cyclic loading and unloading test on the bottom structure of the overlying soil layer at a depth of 100 m: (**a**) amplitude of 19.2 kN; (**b**) amplitude of 38.4 kN; and (**c**) amplitude of 57.6 kN. When the bottom structure was subjected to a 50 m overlying soil layer, an impact load of 192 kN was applied (Figure 24). The load-displacement curve (Figure 24a) exhibited more pronounced nonlinear behavior compared to the uncovered scenario. The repeated loading and unloading cycles resulted in significant deformation, particularly during the higher amplitude loading sequences. The earth pressure gauges recorded peak loads with the highest value in channel 2 and the lowest in channel 5. The presence of the overlying soil layer significantly influenced the stress distribution and mechanical response, leading to more severe deformation and potential for damage. The bottom structure sample showed fractured pillars between the ore accumulation troughs and signs of peeling failure in the trough walls (Figure 25). Figure 22: The mechanical properties of the bottom structure without overlying soil layer under the impact of 192 kN large rockfall: (**a**) load–displacement curve; (**b**) soil pressure–normalized time curve; (**c**) strain–normalized time curve. Figure 23: Characteristics of bottom structure failure under no overlying load and large block impact: (**a**) broken pillar between funnels and (**b**) broken pillars. Figure 24: Mechanical characteristics of the bottom structure of the 50 m overlying soil layer under the impact of a 192 kN large rockfall: (**a**) load–displacement curve; (**b**) soil pressure–normalized time curve; (**c**) strain–normalized time curve. For the bottom structure with a 100 m overlying soil layer, an impact load of 192 kN was applied (Figure 26). The load-displacement curve (Figure 26a) demonstrated even more pronounced nonlinear behavior. The repeated loading and unloading cycles resulted in significant deformation, particularly during the higher amplitude loading sequences. The earth pressure gauges recorded peak loads with the highest value in channel 2 and the lowest in channel 5. The thicker overlying soil layer resulted in higher static and dynamic forces acting on the bottom structure, leading to more severe deformation and potential for damage. The bottom structure sample showed fractured pillars between the ore accumulation troughs, cracking at the arch of the ore extraction route, and significant peeling and damage to the trough walls (Figure 27). The damage observed in the bottom structure under large block collapse impact can be attributed to several key mechanisms. (1) High-Energy Impact Loading: The sudden release of high-energy impacts from large rock blocks results in significant stress concentrations at critical locations such as the ore accumulation troughs and the pillars between troughs. The high-magnitude impact loads cause immediate and localized damage, as evidenced by the fractured pillars and peeling of the trough walls (Figures 23, 25 and 27). (2) Stress Wave Propagation: The dynamic nature of the impact loads results in stress wave propagation through the bottom structure. These stress waves can cause dynamic amplification of the applied loads, leading to higher peak stresses than those predicted by static analysis.