## 6 Stability Analysis of Surrounding Rock Based on Refined Modeling
### Refined Computational Model  
Based on the 3D refined numerical model established in Section 2.1, the rock mass strength parameters calculated in Section 2.3 are assigned to the model. During the calculation, normal constraints are applied to the model's sides, and full constraints are applied to the model's bottom. The Mohr-Coulomb constitutive model is used. In this simulation, the goat is set as empty cells. Empty cells refer to cells in the numerical model that exist but do not contain material and are used to represent underground voids, fractures, or other empty areas. These empty cells do not contribute any physical or mechanical properties (such as density, stiffness, etc.) during the simulation process, but their geometric shape is retained in the model to maintain the continuity of the calculations. Taking the Jiangfeng Iron Mine as an example, the size of the mine model is 1890 m \(\times\) 1826 m \(\times\) 1205 m (length \(\times\) width  
\begin{table}
\begin{tabular}{c c c c} \hline
**Sublevel** & **Grade II** & **Grade III** & **Grade IV** \\ \hline
115 Sublevel & Exploration lines 19–21 & Exploration lines 13–19 & Exploration lines 21–24 & Exploration lines 31–36 \\
135 Sublevel & Exploration lines 19–23 & Exploration lines 13–19 & Exploration lines 31–36 \\  & Exploration lines 24–31 & Exploration lines 23–24 & Exploration lines 31–36 \\  & Exploration lines 15–20 & Exploration lines 13–15 & Exploration lines 31–36 \\
220 Sublevel & Exploration lines 24–27 & Exploration lines 20–24 & Exploration lines 31–36 \\  & Exploration lines 28–31 & Exploration lines 27–28 & Exploration lines 31–36 \\ \hline \end{tabular}
\end{table}
Table 4: Rock mass quality distribution intervals for each sublevel, as assessed by GSI.  
Figure 15: Planar distribution cloud map of GSI. (**a**) Planar GSI distribution cloud map of 115 Sublevel; (**b**) planar GSI distribution cloud map of 135 Sublevel; (**c**) planar GSI distribution cloud map of 220 Sublevel.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Plan** & **Operating Condition** & **Mining Sequence** & **Plan** \\ \hline
1 & No isolation pillar & Unidirectional mining & 1 \\
2 & Isolation pillar thickness of 10 m & Unidirectional mining & 2 \\
3 & Isolation pillar thickness of 20 m & Unidirectional mining & 3 \\ \hline \end{tabular}
\end{table}
Table 5: Summary of working conditions for different isolation pillar thicknesses.  
\(\times\) height, with the z-direction varying according to the topographical undulations). The model consists of 1,086,000 computational units and 374,000 nodes, as shown in Figure 16.  
During the numerical simulation calculation of the Jiangfeng Iron Mine, the stope recovery is carried out layer by layer and segment by segment, according to the investigation report. The calculation proceeds until the unbalanced force of the 3D numerical model system reaches 1 \(\times\) 10\({}^{-5}\), which is considered balanced. Then, filling is performed, and the calculation proceeds again until the unbalanced force reaches 1 \(\times\) 10\({}^{-5}\). This process is repeated until the 3D numerical simulation calculation is completed. To further analyze in detail the stability of the surrounding rock during combined mining, two typical profiles, KH1 and KZ1, were selected along the strike of the ore body for stress evolution analysis. The locations of these profiles are shown in Figure 17a.  
Figure 16: The 3D refined numerical model of the Jiangfeng Iron Mine: (**a**) 3D view; (**b**) fault.  
Figure 17: Schematic diagram of typical profiles. (**a**) Location of typical cross-section; (**b**) typical cross-section of KZ1; (**c**) typical cross-section of KH1.