# Numerical Simulation and Engineering Application of Temporary Stress Field in Coal Mine Roadway
## 4 Distribution Characteristics of Temporary Support Stress Field in Unsupported Area  
Different forms of support induce distinct stress fields in the surrounding rock, as a slender rod-like element, the rock bolt induces a stress field in the surrounding rock that far exceeds its own dimensions [72; 73; 74; 75]. To study the effect of temporary support on the unsupported area, it is essential to initially analyze the stress field generated by the temporary support in that area. However, the FLAC3D5.0 software cannot directly compute the temporary support stress field diffusing into the unsupported area [76; 77; 78; 79]. Therefore, two sets of simulation experiments, A and B, were conducted to simulate the excavation and support of the same roadway. Experiment A represents the case without temporary support after excavation, and Experiment B represents the case with temporary support after excavation. By analyzing the stress differences between these two sets of experiments, the distribution characteristics of the temporary support stress in the unsupported area can be determined. The relevant surrounding rock parameters of Xiao hoadang Mining Company are detailed in Table 1.  
As shown in Figures 4 and 5, the investigation of the stress field distribution characteristics in the surrounding rock of the unsupported area indicated that although the temporary support did not directly support the unsupported area, significant stress fields would still be generated there. The occurrence of these stress fields in the unsupported area can be attributed to the distribution of the temporary support force [80; 81; 82; 83].  
The variation law of the stress field of the temporary support in different height planes was investigated, and it was observed that the stress initially increased and subsequently decreased with increasing height. This difference may result from variations in the distribution of the temporary support force at different heights. This variation law is consistent with the rule obtained from the mathematical model (Figure 3b), which also verifies the model's accuracy. In addition, there is a significant stress difference between the maximum stress at 3 m and the stress at other heights, which will result in a greater risk of roof separation at 3 m. Therefore, caution should be exercised when utilizing temporary support at the layered roof position. Furthermore, the stress field of the bolt support first decreases and then increases with an increase in height. Therefore, temporary support can complement bolt support effectively and improve the stability of the surrounding rock before permanent support [84; 85].  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Simulation** & \begin{tabular}{c} **Area of** \\ **Section (m\({}^{2}\))** \\ \end{tabular} & \begin{tabular}{c} **L\({}_{1}\)** \\ **(m)** \\ \end{tabular} & \begin{tabular}{c} **L\({}_{2}\)** \\ **(m)** \\ \end{tabular} & \begin{tabular}{c} **L\({}_{3}\)** \\ **(MPa)** \\ \end{tabular} & \begin{tabular}{c} **F** \\ **(MPa)** \\ \end{tabular} & \begin{tabular}{c} **Density** \\ **(MPa)** \\ \end{tabular} & \begin{tabular}{c} **Shear** \\ **(MPa)** \\ \end{tabular} & \begin{tabular}{c} **Bulk** \\ **(MPa)** \\ \end{tabular} & \begin{tabular}{c} **Tension** \\ **(MPa)** \\ \end{tabular} & \
\begin{tabular}{c} **Cohesion** \\ **(MPa)** \\ \end{tabular} &
\begin{tabular}{c} **Friction** \\ **(MPa)** \\ \end{tabular} \\ \hline A & \(6\times 5\) & 5 & 0 & 10 & 0 & 1400 & 6000 & 4000 & 0.4 & 2 & 25 \\ \hline B & \(6\times 5\) & 5 & 5 & 10 & 6 & 1400 & 6000 & 4000 & 0.4 & 2 & 25 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Simulation parameter.  
Figure 4: Stress nephogram at different heights from the roof.  
Figure 5: Comparison of stress curves at different heights from the roof.