## 4 Experimental Procedures  
The evaluation of the bottom structure's bearing capacity necessitates a meticulously designed experimental protocol. Given the large dimensions of the bottom structure specimen (0.8 m \(\times\) 0.8 m \(\times\) 0.8 m), a three-phase five-sided large-scale testing machine was deemed appropriate to accommodate the specimen size and simulate the complex loading conditions. The experimental setup involved applying a combination of static and dynamic loads to the bottom structure model, with multiple monitoring points strategically positioned to capture the mechanical response under various load scenarios.  
Prior to loading, strain gauges were affixed to critical locations on the bottom structure model, including the ore accumulation trough, the roadway, and the ore extraction route, as illustrated in Figure 15. This arrangement enabled real-time monitoring of strain variations  
Figure 14: The impact stress of unstable rock mass collapse on the bottom trough in the northeast slope: (**a**) front section impact stress; (**b**) post-impact stress.  
at different positions during the test, thereby providing insights into the localized damage and deformation characteristics of the structure.  
To facilitate the routing of data cables from the strain gauges and stress meters, four bottom partitions were preinstalled between the loading plate and the bottom structure model. The dimensions of these partitions were carefully designed to match the size of the vein tunnel, ensuring sufficient space for the data cables while maintaining the structural integrity of the test setup.  
During the loading process, the three-phase five-sided loading device was employed to apply the predetermined loads. Figure 16 presents a top view of the loading setup, highlighting the importance of maintaining a uniform confining pressure of 0.1 MPa around the specimen. This pressure level was selected to prevent excessive compaction of the granular material while ensuring the stability of the specimen during the test, thereby mimicking the natural caving conditions in a block caving mine.  
The experimental system integrated a loading control system, a stress acquisition system, a strain acquisition system, and a bulk pressure acquisition system, as depicted in Figure 16. The loading was controlled based on the force value, with a loading rate of 1 kN/s. Throughout the experiment, the stress and strain data were independently monitored and recorded by two separate computers, each equipped with specialized software and hardware. This dual-monitoring approach ensured the accuracy and reliability of the data, allowing for comprehensive analysis of the mechanical behavior of the bottom structure under different loading conditions.  
Based on the numerical simulation results of slope collapse impact stress, the loading scenarios were categorized into three distinct types, as shown in Figure 17. These types included the overall collapse impact curve (Figure 17a), the partial collapse large block impact curve (Figure 17b), and the progressive collapse multiple impact curve (Figure 17c). Each type of loading was carefully designed to replicate the actual impact forces that the bottom structure might experience during slope collapse events in block caving mines. The static load corresponding to the actual height of the caving ore and rock was taken into account, and the dynamic disturbance loads were applied according to the stress values obtained from the numerical simulations.  
Figure 15: Adhesive of bottom structure strain gauges.  
Figure 16: Experimental system: (**a**) loading system; (**b**) stress collection system; (**c**) strain acquisition system; (**d**) bulk pressure collection system.  
Figure 17: Characteristic curve of impact load on landslide mass: (**a**) overall collapse impact curve; (**b**) partial collapse large block impact curve; and (**c**) progressive collapse multiple impact curve.