## 3 Model Building and Validation  
### Model Building  
In this paper, the West Second Mining Area of Jinchang Longshou Mine was taken as the engineering background, and a large-scale 1:1 true 3D numerical model was built by using multiple software modeling methods, reflecting the real relative position of the ore body and the fault as well as the spatial distribution status of the two mining methods. The refined numerical simulation was used to analyze the changes in stress and displacement fields of the fault surface and the ore body near the fault, as well as the surface displacement and movement patterns caused by mining under different working conditions. We utilized AutoCAD 2020, the 3D modeling function of Rhino 7, the powerful meshing function of ANSYS 2021R2, and the excellent computational function of FLAC3D 6.0 to ensure the reliability of the results (Figure 4). Due to the complexity of modeling and the limited data available, the modeling in this paper focused on the main factors affecting the stability of the roadway, including the geological structure, fault morphology, ground stress state and strength parameters.  
Figure 3: Relative position of the ore body and the fault.  
Figure 2: Structural diagram of the caving method.  
The size of the model was 3000 m (x) \(\times\) 2300 m (y) \(\times\) 1050 m (z), the number of cells was 862,524, the number of nodes was 147,117 and the Moore-Cullen strength criterion was adopted.  
The rock mass in this simulation is an ideal elastoplastic stress-strain model, and the Moore-Cullen yield criterion describes:  
\[f_{s}=\sigma_{1}-\sigma_{3}\frac{1+sin\varphi}{1-sin\varphi}-2c\sqrt{\frac{1+ sin\varphi}{1-sin\varphi}} \tag{1}\]  
Inside the official: \(\sigma_{1}\) and \(\sigma_{3}\) are the maximum principal stress and the minimum principal stress. \(c\) is the adhesion force, and \(\varphi\) is the friction angle. When >0, shear failure occurs.  
The surface of the calculation model is a free boundary, which constrains two X-axis displacements perpendicular to the X-axis direction and two Y-axis displacements perpendicular to the Y-axis direction. Gradient stress is applied to the model boundary according to the actual ground stress:  
\[\left\{\begin{array}{ll}\sigma_{1}=2.13+0.037H\;\;\text{MPa}\\ \sigma_{2}=1.12+0.0159H\;\;\text{MPa}\\ \sigma_{3}=1.106+0.032H\;\;\text{MPa}\end{array}\right. \tag{2}\]  
where \(\sigma_{1}\), \(\sigma_{2}\) and \(\sigma_{3}\) are the maximum principal stress, minimum principal stress and vertical principal stress (MPa), respectively; \(H\) is the depth (m).  
The model is shown in Figure 5. The yellow part of Figure 5 shows the filling body, and the cemented backfill is usually composed of aggregate, gelling agent, water and other components, and the mechanical properties of the backfill are significantly improved due to the addition of gelling agent. The internal friction angle of the backfill is 38\({}^{\circ}\), the cohesion of the backfill is 0.95 Mpa, and the tensile strength of the backfill is 0.8 Mpa [39]. The filling of a single approach in the downward horizontal layered cementation filling method is often divided into two parts: the lower part of the approach adopts the filler with higher strength (4-5 Mpa), and the upper part adopts the filler with relatively low strength (2\(\sim\)3 Mpa) [40].  
The values of each mechanical parameter (Table 1) refer to the results of the mine's ore and rock mechanics test, and the mechanical parameters mainly include ore and rock density \(\rho\), bulk modulus K, ore and rock cohesion c, internal friction angle \(\varphi\) and the tensile strength of rock mass.  
Figure 4: Modeling flowchart.  
The specific locations of the fault deployment monitoring points are shown in Table 2.  
The specific locations of the monitoring points.  
The specific locations of the fault deployment monitoring points are shown in Table 2.