## 4 Stability Evaluation and Comparative Analysis of Goafs Based on Field Monitoring
### Monitoring and Analysis of Surrounding Rock Deformation  
We conducted surrounding rock deformation monitoring using both a commercially available steel ruler with a precision of 0.5 mm as a multi-point displacement meter and the JSS30A digital convergence meter produced by Beijing ZhongCoal Mining Engineering Co., Ltd. Six displacement monitoring points, N18-1#, N17-1#, along vein-1#, along vein-3#, main lane-1#, and main lane-2# around mine 1#, were selected for measurement and are represented by points 1, 3, 5, 7, 8, and 9, respectively. The displacement data of six monitoring points are shown in Table 11.  
Figure 11: Stress monitoring data trend chart.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Sampling Number** & **Sampling Time** & **Sampling Value** & **Stress 1** & **Stress 2** & **Stress 3** & **Stress 4** \\ \hline
1 & 5 September 2010 & P & 3.731 & 3.798 & 3.635 & 3.721 \\
2 & 16 September 2010 & P & 3.117 & 2.608 & 2.702 & 3.285 \\
3 & 30 September 2010 & P & 2.686 & 2.230 & 1.897 & 2.911 \\
4 & 11 November 2010 & P & 2.439 & 2.041 & 1.426 & 2.723 \\
5 & 21 January 2011 & P & 1.818 & 1.470 & 1.087 & 1.780 \\
6 & 25 February 2011 & P & 0.944 & 1.025 & 0.952 & 1.46 \\
7 & 23 March 2011 & P & 1.19 & 1.28 & 1.29 & 1.72 \\
8 & 22 April 2011 & P & 2.00 & 2.55 & 2.64 & 2.47 \\
9 & 24 May 2011 & P & 3.06 & 3.86 & 3.97 & 3.47 \\
10 & 25 June 2011 & P & 3.55 & 4.17 & 4.36 & 3.85 \\
11 & 25 July 2011 & P & 3.85 & 4.29 & 4.49 & 3.97 \\ \hline \end{tabular}
\end{table}
Table 10: Comparison of the results of two evaluation methods.  
The resulting data graph is shown in Figure 12. According to the monitoring data of strain, the stress of the pillar changes sharply during mining and bears the main stress; moreover, the horizontal displacement and the deformation are evident. The change of the displacement monitoring points on both sides of the mine is smaller than that of the pillar, which indicates that the disturbance of the mining room on both sides is less than that of the pillar. The change of the displacement monitoring points on the main roadway is the least, which indicates that the disturbance of the main roadway is less. Overall, the rock displacement changes slightly and stabilizes with the progress of mining, which indicates that the whole goal is in a stable state.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Sampling Number** & **Sampling Time** & **Point 1** & **Point 3** \\ \hline
2 & 5 September 2010 & 2.5 m + 13.67 mm & 2.5 m + 12.98 mm \\
3 & 16 September 2010 & 2.5 m + 12.72 mm & 2.5 m + 12.12 mm \\
4 & 30 September 2010 & 2.5 m + 12.72 mm & 2.5 m + 12.09 mm \\
5 & 11 November 2010 & 2.5 m + 12.72 mm & 2.5 m + 12.02 mm \\
6 & 21 January 2011 & 2.5 m + 9.25 mm & 2.5 m + 8.56 mm \\
7 & 25 February 2011 & 2.5 m + 9.94 mm & 2.5 m + 9.99 mm \\
8 & 23 March 2011 & 2.5 m + 11.34 mm & 2.5 m + 11.75 mm \\
9 & 22 April 2011 & 2.5 m + 12.12 mm & 2.5 m + 12.01 mm \\
10 & 24 May 2011 & 2.5 m + 12.54 mm & 2.5 m + 12.09 mm \\
11 & 25 June 2011 & 2.5 m + 12.88 mm & 2.5 m + 12.76 mm \\ \hline
**Sampling Number** & **Point 5** & **Point 7** & **Point 8** & **Point 9** \\ \hline
2 & 3.5 m + 12.89 mm & 3.5 m + 13.02 mm & 7.575 m + 6.72 mm & 5.20 m + 8.68 mm \\
3 & 3.5 m + 10.98 mm & 3.5 m + 11.23 mm & 7.575 m + 6.35 mm & 5.20 m + 8.61 mm \\
4 & 3.5 m + 9.13 mm & 3.5 m + 9.68 mm & 7.575 m + 7.23 mm & 5.20 m + 8.85 mm \\
5 & 3.5 m + 8.48 mm & 3.5 m + 8.96 mm & 7.575 m + 6.41 mm & 5.20 m + 8.27 mm \\
6 & 3.5 m + 7.96 mm & 3.5 m + 7.88 mm & 7.575 m + 5.05 mm & 5.2 m + 7.47 mm \\
7 & 3.5 m + 8.56 mm & 3.5 m + 9.80 mm & 7.575 m + 4.93 mm & 5.25 m + 7.11 mm \\
8 & 3.5 m + 9.99 mm & 3.5 m + 10.13 mm & 7.575 m + 6.83 mm & 5.20 m + 8.85 mm \\
9 & 3.5 m + 10.08 mm & 3.5 m + 10.76 mm & 7.575 m + 7.41 mm & 5.20 m + 8.97 mm \\
10 & 3.5 m + 10.26 mm & 3.5 m + 10.88 mm & 7.575 m + 7.55 mm & 5.2 m + 9.47 mm \\
11 & 3.5 m + 10.56 mm & 3.5 m + 11.23 mm & 7.575 m + 7.93 mm & 5.25 m + 9.98 mm \\ \hline \end{tabular}
\end{table}
Table 11: Displacement monitoring point data sheet.  
Figure 12: Strain monitoring data diagram.