## 4 The Process of Changing Mining Methods in Mines
### Optimization of Structural Parameters of the Stope
(b) The maximum tensile stress and maximum compressive stress of each modeling scheme gradually increase with the increase in the stope span, indicating that the stability of the stope is getting worse with the increase in the stope span. (c) The maximum compressive stress and maximum tensile stress of the roof plate of each model did not exceed the ultimate compressive strength and tensile strength values, but the fact that the mechanical strength values of the ore meet the requirements does not mean that the strength values of the ore body can also meet the safety requirements. This is due to the existence of joints, fissures, and other geologically weak surfaces; the compressive strength and tensile strength values of the ore body are significantly lower. 6. Calculation of safety factor  
There are many factors affecting the safety of the roof, such as the mechanical properties of the rock, the development of joints and fissures, the intensity of mining (exposure time), blasting parameters, support methods, structural parameters of the stope, and so on, and due to the limitations of numerical simulation technology, the simulation results cannot be guaranteed to be 100 percent accurate. Therefore, for safety reasons, the safety coefficient method can be used to evaluate the roof stability of the stope. The safety coefficient is defined as the ratio of the compressive strength (or tensile strength) of the ore rock to the maximum compressive stress (or tensile stress) of the roof plate, and the safety coefficients of tensile and compressive strength of each model under the conditions of the roof plate of the ore body are shown in Table 4.  
Since the roof of the stope is mainly damaged by tensile pressure, it is considered that the tensile stability of the roof is better when the tensile safety coefficient \(\eta_{1}\) is \(\geq\)1.15, while the compressive safety coefficient \(\eta_{2}\) can be considered to be good as long as it is greater than 1.0, taking into account the maximum compressive and tensile stress values of each model in the table. According to this criterion, and considering the efficiency and economic factors, model 2, that is, the safety and reliability of the sublevel open stope subsequent filling method with 18 m of mine pillar and 18 m of mine room, is higher, and the economic indexes are also more ideal. To summarize, when recommending Luohe iron ore mine to adopt the sublevel open stope subsequent filling method, the mine's current-formed stope structure parameters of 18 m for the pillar and 18 m for the mine room are reasonable. If, in the process of mining, it is found that the solidity of some sections is poor, the specifications of the stope can be appropriately reduced. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{2}{c}{**Serial Number**} & \multicolumn{2}{c}{**Compressive Safety Factor**} & **Tensile Safety Factor** \\ \hline \multirow{2}{*}{Model 1} & Condition 1 & 15.5 & 6.86 \\ \cline{2-4}  & Condition 2 & 13.2 & 1.39 \\ \hline \multirow{2}{*}{Model 2} & Condition 1 & 13.6 & 5.53 \\ \cline{2-4}  & Condition 2 & 13.1 & 1.38 \\ \hline \multirow{2}{*}{Model 3} & Condition 1 & 11.5 & 3.03 \\ \cline{2-4}  & Condition 2 & 7.7 & 1.15 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Table of tensile and compressive safety coefficients for combinations of parameters.