## 2 Stability Classification of Goafs Based on CMS Measurement and Numerical Simulation
### Construction of 3D Solid Model of Goafs Based on CMS Detection  
The 3D laser CMS is a cavity detection system for underground mines developed by Noranda Technology Center and Optech Systems. In this paper, CMS is used to detect 34 goaf areas in Shiregou Iron Mine, and each surveyed goaf area is divided into six parts according to spatial orientation, namely, south of F18 fault, between F18 and F19 faults, north end of south mining area, north branch, inclined mining area, and measure well mining area, as shown in Table 1. The detection data from the CMS for probing the goaf areas can be directly imported into 3 DMine software. After solid editing and verification, solid models for each goaf area are generated. A diagram of the 3D solid models of the goaf areas is shown in Figure 2, where the positions of the goaf areas do not represent their spatial relationships.  
3 Dmine is used to establish a solid model of each goaf, and more accurate goaf volume can be estimated through the solid model volume estimation function of the software to prepare for the later goaf-filling work. The volume of each goaf is shown in Table 1.  
The total volume of the measured goaf areas reaches 298,215 m\({}^{3}\), as shown in Table 1. Among them, 63% of the goaf volume is greater than 5000 m\({}^{3}\); under the influence of these large-volume goafs, the risk of mining is high. By combining the solid model with FLAC3D numerical simulation software, further mechanical analysis is performed to evaluate goaf stability and its influence on the mining area and to determine goaf stability and the next treatment method.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Block Name** & **Goaf Number** & **Volume (m\({}^{3}\))** & **Block Name** & **Goaf Number** & **Volume (m\({}^{3}\))** \\ \hline \multirow{3}{*}{South of the F18 fault (3)} & F18N-10\# & 2560 & & XJ-2\# & 2656 \\  & F18N-12\# & 998 & & XJ-3\# & 3344 \\  & F18N-13\# & 1253 & & XJ-4\# & 13,670 \\  & DCJ-1\# & 2500 & & XJ-7\# & 13,344 \\  & DCJ-3\# & 2640.69 & & XJ-24\# & 16,000 \\  & DCJ-6\# & 1984.38 & & XJ-39\# & 20,981 \\  & NCB-3\# & 23,444 & & XJ-40\# & 24,274 \\  & NCB-8\# & 1469 & & CSJ-2\# & 12,544 \\  & NCB-10\# & 2745 & & CSJ-3\# & 5440 \\  & NCB-17\# & 9008 & & CSJ-4\# & 3648 \\  & NCB-19\# & 6208 & & CSJ-5\# & 7050 \\  & BFZ-2\# & 11,594 & Measure well & CSJ-6\# & 1269 \\  & BFZ-3\# & 2298 & mining area (10) & CSJ-7\# & 5327 \\  & BFZ-6\# & 6831 & & CSJ-8\# & 12,750 \\  & BFZ-8\# & 8192 & & CSJ-11\# & 12,672 \\  & BFZ-9\# & 21,304 & & CSJ-X\# & 3456 \\ Inclined shaft mining & \multirow{2}{*}{XJ-1\#} & \multirow{2}{*}{11,313} & \multirow{2}{*}{CSJ-12\#} & \multirow{2}{*}{Cut through 23,448} \\  & & & & & \\ area (8) & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: The measured volume of each goaf area.  
Figure 1: Composite diagram of each goaf with 0 m roadway, \(-60\) m roadway, and surface solid model. The green part of the model in the figure represents the surface entity model, the blue part represents the roadway at 0 m and \(-60\) m levels, and the red and yellow models represent various goafs.