## 1 Introduction
Traditional finite element (FEM) and finite difference (FDM) methods fall short in capturing rock crack propagation, as well as the movement and rotation of fragmented rock masses, thus hindering the simulation of ore body collapse processes [22]. Moreover, discrete element simulations often inadequately represent fissures within surrounding rocks. Computational constraints necessitate the use of large mesh sizes, failing to reflect the diffuse damage and rupture mechanics of rock bodies. Additionally, most discrete element simulations employ planar strain models, lacking three-dimensional fidelity [23]. [PERSON] et al. [17; 24] employed three-dimensional numerical difference simulations to investigate the stability of bottom structures in natural chipping mining processes, specifically under pre-excavation conditions, offering pertinent support recommendations. [PERSON] et al. [25] observed stress concentration in bottom structure areas, such as roadway intersections, as mining progressed, potentially leading to roadway damage. [PERSON] et al. [26; 27] employed FLAC3D simulation software to establish numerical models combined with the pressure arch theory, exploring the evolution of pressure arches during the bottom collapse process in block caving methods. However, the finite element-discrete element coupling method (FDEM), combining the advantages of continuum and discontinuum methods, seamlessly transitions from continuous to discontinuous mediums through deformation, fracture, and fragmentation, thereby simulating the damage and fracture processes of rocks [28; 29]; meanwhile, its numerical models directly correlate with the microscopic mechanical parameters of rocks [30]. [PERSON] et al. [31; 32] consider physical simulation experiments on engineering rock masses to be an important method for studying rock engineering problems, with the selection of materials for physical models being crucial for the success of experiments. [PERSON] et al. [33], based on similarity simulation experiments, investigated the influence of newly constructed coal bins on the movement of underlying rock layers and the strain characteristics of surrounding rocks. [PERSON] et al. [34], through similarity material simulation tests on the block caving method in lean ore de posits, obtained the collapsibility, collapse mechanism, and collapse rate during the bottom extraction process, providing necessary theoretical basis for the design and construction of the block caving method in lean ore deposits in Jinchuan. [PERSON] et al. (2019); [PERSON] et al. (2020); [PERSON] et al. (2020) found that after the stable structure formation of side-by-side accumulations, under the influence of overlying rock movement, the movement of overlying rock may lead to phenomena such as the squeezing of side-by-side accumulations into roadways. In the actual production of natural collapse method mines, the advancement of bottom pulling blasting under horizontal geostress has resulted in the evolution of bottom structure ground pressure disasters, characterized by repeated pressure. However, previous research has not fully revealed the evolution, characteristics, and mechanisms of bottom structure ground pressure disasters in natural collapse methods. This study utilized GPI-3D-FDEM (Enhanced 3D Finite Element-Discrete Element Coupling Analysis Method Based on GPU Parallel Computing) to simulate the collapse characteristics of the No. II ore body in Tong Shan Mine under various bottom excavation conditions. After reviewing the current research landscape regarding the use of similar materials in physical simulations of engineering rock formations, we applied the principle of similarity to conduct simulation tests on the chipping phenomenon. Our analysis comprehensively examines stress and displacement variations throughout the entire avalanche process, aiding in establishing a rational bottom pulling scheme and sequence. This investigation also identifies the initial area of avalanches and areas of sustained avalanches.