## 3 Numerical Simulation of Full-Columnar Overburden
### Simulation Results of Models with Different Mining Heights  
Figure 4 shows the cloud diagram of overburden displacement change in Scheme 1 during the mining process. When the working face advances to 50 m behind the NLC, a 0.1 m-thick separation layer appears below KS1 in the NLC. When the working face advances 100 m behind the NLC, the maximum separation thickness below KS1 is about 0.6 m. When the working face advances to 200 m behind the NLC, the separation layer below KS1 is about 0.2 m. From KS2 to KS4, there is no obvious separation layer. Figure 5 shows the monitoring data curves of displacement and stress obtained from measuring points of each key stratum in NLC in Scheme 1. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Scheme Number** & **Mining Height (m)** & **Mining Width (m)** \\ \hline
1 & 3 & 300 \\
2 & 4 & 300 \\
3 & 5 & 300 \\
4 & 5 & 250 \\
5 & 5 & 350 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulation schemes for different mining parameters. Figure 4: Cloud Diagram of displacement change of Scheme 1 when the working face advances to a range of 200 m behind the NLC: (**a**) 50 m; (**b**)100 m.  
Figure 5: Displacement and stress curves of each measuring point in NLC in Scheme 1: (**a**) Displacement curves; (**b**) Stress curves. As is shown in Figure 5a, when the working face is in advance of NLC, the upper rock mass is more susceptible to advance compression than the lower rock mass. The upper rock strata KS4 to PKS begin to produce compression deformation at a distance between the working face and the NLC with \(-\)300 m (the minus sign means the position of the working face is ahead of NLC), while the lower rock strata KS1 to KS3 begin to produce compression deformation at a distance between the working face and the NLC with \(-\)200 m. When the working face advances past NLC, the displacement from KS1 to KS3 changes greatly, while the displacement above KS4 changes slightly. When the working face advances past NLC by 100 m, the maximum subsidence of KS1 is about 2.33 m.  
As is shown in Figure 5b, when the working face advances ahead NLC 90 m, stress concentration is generated within the range of KS1 to KS3 due to advanced compression, and the peak stress reaches 17.55 MPa. When the working face continues to advance to right below NLC, obvious fractures appear in KS1, and the stress of this stratum is relieved to 0 Mpa sharply. When the working face advances past NLC by 50 m, KS2 and KS3 are fractured, and the stress values of the corresponding strata are depressurized to 0 Mpa. At this time, KS4 also witnesses a large stress relief, but the stress does not drop to 0 Mpa. The stress from KS5 to PKS does not show a large relief, indicating that there is no fracture. After the working face is pushed past NLC by 150 m, the stress monitored at the measuring points in each key stratum tends to be stable, indicating that the lower goat is in a state of compaction. Based on the analysis results in Figure 5, it can be concluded that the stress at measuring points from KS1 to KS3 has a sharp pressure relief and the subsidence displacement increases sharply synchronously, indicating that the three key strata have broken. However, from KS4 to PKS, the stress reduction rate is slow, and the lowest stress is much higher than 0 MPa, while the subsidence displacement increases slowly, indicating that only bending subsidence of varying degrees occurs from KS4 to PKS, but no obvious fracture occurs. Figure 6 shows the cloud diagram of overburden displacement change in Scheme 2 during the mining process. When the working face advances to 50 m behind the NLC, a 0.5 m-thick separation layer appears below KS1 in the NLC. When the working face advances 100 m behind the NLC, the thickness of separation layer below KS1 increases to 1 m; meanwhile, separation layer also appears below KS2 and KS3.