## 4 Conclusions  
In this study, we utilized GPI-3D-FDEM software to establish an N-H hyperelastic intrinsic numerical simulation model based on the actual engineering parameters and physical parameters of the mine. The simulation process adhered to the backward bottom pulling method. Additionally, similar simulation experiments were conducted in conjunction with an indoor physical model to verify the correctness of the proposed simulation experiments. Subsequently, we systematically investigated the stress evolution law of the bottom structure during the bottom pulling advancement process of the natural collapse method, revealed the mechanisms behind ground pressure disasters in the bottom structure, guided the production of the natural collapse method under horizontal ground stress, and provided reference values for rock damage assessment. Through our analysis, the following conclusions were drawn:  
1. Analysis from three-dimensional numerical simulation calculations revealed that as the range of bottom pulling expanded, stress redistribution was increasingly disrupted, and the vertical stress unloading of the top and bottom plates became obvious, gradually forming an unloading funnel under the influence of bottom pulling. This disruption led to stress concentration in local areas around the collapsed arch, specifically on both sides of the arch top and in the bottom pulling area. Moreover, when the fracture zone extended to the rock mass above the bottom pulling area, the horizontal stress distribution gradually lost symmetry, and the degree of horizontal stress concentration increased with the expansion of the bottom pulling area.
2. A comprehensive analysis combining three-dimensional numerical simulation and two-dimensional similar material simulation tests concluded that the stress in the rock layer surrounding the bottom pulling roadway exhibited periodic changes. This analysis also demonstrated consistency in the chipping law along both perpendicular and parallel ore body strikes. Additionally, the displacement and deformation exhibit a deep \"V\"-type configuration. Before the top plate broke, stress values in the layer increased, followed by a decrease after the top plate breakage, indicating energy release in the rock layer. Upon entering the pull-down space, stress changes were influenced by overburden movement and the compression of broken rock layers, resulting in wave-like fluctuations that eventually stabilized.
3. Tensile stress concentration in the lower layer beneath the pulling bottom area of the structure increases with the pulling bottom area's expansion. Horizontal stress from natural collapse leads to a stress sequence of \"initial compression, followed by tension\". Upon increasing the pulling bottom area, compressive and tensile stress concentrations intensify. This phenomenon manifests during actual bottom structure production. The stress state of the structure is affected by the bulk ore load in the quarry, resulting from the uneven discharge of the quarry, leading to an uneven distribution of the ore bulk load. Hence, further investigation is needed into how the uneven ore discharge affects bottom structure stress distribution.  
Validation, L.X.; investigation, X.Q.; writing--review and editing, Z.L.; project administration, X.Y.; funding acquisition, H.C. All authors have read and agreed to the published version of the manuscript.  
This work is financially supported by the National Key Research and Development Project of China (2023 YFC2907403), Fundamental Research Funds for the Central Universitys (06500229).  
Not applicable.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
Authors [PERSON] and [PERSON] were employed by the company BGRIMM Technology Group, Beijing. The remaining authors declare that the research was conductedin the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.