## 3 Numerical Simulation of Full-Columnar Overburden
### Simulation Results of Models with Different Mining Heights
When the working face advances to 150 m behind the NLC, the separation layer below KS1 and KS2 tends to close, and the maximum thickness of the separation layer below KS3 is 0.5 m. When the working face advances to 200 m behind the NLC, the separation layer below KS1 and KS3 tends to close. No obvious separation layer is observed below KS4 throughout the whole process. Figure 7 shows the monitoring data curves of displacement and stress obtained from measuring points of each key stratum in NLC in Scheme 2. Figure 6: Cloud Diagram of displacement change of Scheme 2 when the working face advances to a range of 200 m behind the NLC: (**a**) 100 m; (**b**) 150 m.  
As is shown in Figure 7a, when the working face is in advance of NLC, the upper rock strata KS4 to PKS begin to produce compression deformation at a distance between the working face and the NLC with \(-250\) m due to the impact of advance compression. By contrast, compression deformation occurs in KS1 to KS3 at a distance between the working face and the NLC with \(-150\) 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 150 m, the maximum subsidence of KS1 is about 3.19 m.  
As is shown in Figure 7b, when the working face advances ahead NLC70m, stress concentration is generated within the range of KS1 to KS3 due to advanced compression, and the peak stress reaches 17.44 MPa. When the working face continues to advance past NLC by 15 m, 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 is fractured completely; when the working face advances past NLC by 100 m, KS3 is fractured completely. The stress of the corresponding strata is depressurized to 0 MPa. Meanwhile, the stress from KS4 to PKS does not show a large relief, indicating that there is no fracture. Figure 8 shows the cloud diagram of overburden displacement change in Scheme 3 during the mining process. When the working face advances to 50 m behind the NLC, a 1.1 m-thick separation layer appears below KS1. As the working face continues to advance, the separation layer below KS2 and KS3 tends to close, and the maximum thickness of the separation layer below KS3 is 1.0 m. When the working face advances to 200 m behind the NLC, the separation layer below KS1 and KS2 tends to close, and the separation layer below KS3 is approximately 0.9 m. No obvious separation layer is observed below KS4 throughout the whole process. Figure 8: Cloud Diagram of displacement change of Scheme 3 when the working face advances to a range of 200 m behind the NLC: (**a**) 50 m; (**b**) 200 m.  
Figure 7: Displacement and stress curves of each measuring point in NLC in Scheme 2: (**a**) Displacement curves; (**b**) Stress curves. Figure 9 shows the monitoring data curves of displacement and stress obtained from measuring points of each key stratum in NLC in Scheme 3. As is shown in Figure 9, when the working face is in advance of NLC, the upper rock strata KS4 to PKS begin to produce compression deformation at a distance between the working face and the NLC with \(-200\) m due to the impact of advance compression. By contrast, compression deformation occurs in KS1 to KS3 at a distance between the working face and the NLC with \(-100\) m. When the working face advances past NLC by \(150\) m, the maximum subsidence of KS1 is about \(4.34\) m.  
As is shown in Figure 9, when the working face advances ahead NLC \(100\) m, stress concentration is generated remarkably within the range of KS1 to KS3, and the peak stress reaches \(16.22\) MPa. When the working face continues to advance to right below NLC, obvious fractures appear in KS1, and the stress of this stratum is released to \(0\) Mpa sharply. When the working face advances past NLC by \(50\) m, KS2 and KS3 are fractured completely; the stress of the corresponding strata is depressurized to \(0\) MPa.