## 3 Law of Strata Fracture Movement
### Monitoring of Strata Deformation  
In the mining process, the increase in goat area can cause large-scale surface subsidence and even cause secondary disasters such as collapse. Therefore, a number of strata movement lines are arranged on the surface of the 12-panel area of the mine to monitor the change in surface settlement caused by mining in LW 1208 (seen in Figure 6). \begin{table}
\begin{tabular}{c c c c c c} \hline
**Detection** & **Detection** & **Distance from** & **Stratigraphic** & **Detection Date** & **Spatial Relationship with** \\
**Hole Name** & **Position Name** & **2-2 Coal Seam/m** & **Name** & **Mining Location** \\ \hline \multirow{3}{*}{A} & A\({}_{1}\) & 345.9 & K\({}_{\rm 1 zh}\) & 12 March 2020 & 69.4 m behind detection hole A \\  & A\({}_{2}\) & 320.5 & J\({}_{\rm 2a}\) & 15 May 2020 & 297.7 m in front of detection hole A \\  & A\({}_{3}\) & 221.8 & J\({}_{\rm 2z}\) & & \\ \hline \multirow{3}{*}{B} & B\({}_{1}\) & 352.3 & K\({}_{\rm 1 zh}\) & 15 May 2020 & 147.3 m behind detection hole B \\  & B\({}_{2}\) & 315.2 & J\({}_{\rm 2a}\) & 15 July 2020 & 247.8 m in front of detection hole B \\  & B\({}_{3}\) & 219.5 & J\({}_{\rm 2z}\) & & \\ \hline \multirow{3}{*}{C} & C\({}_{1}\) & 447.6 & K\({}_{\rm 1 zh}\) & 24 July 2021 & 74.9 m behind detection hole C \\  & C\({}_{2}\) & 444.8 & K\({}_{\rm 1 zh}\) & 23 August 2021 & 29.9 m in front of detection hole C \\  & C\({}_{3}\) & 310.2 & J\({}_{\rm 2a}\) & & \\ \hline \end{tabular}
\end{table} 
Table 2: Detailed layout of detection positions of detection holes A, B, and C.  
As of 26 April 2021, LW 1208 is in the solid coal mining stage, the evolution of surface subsidence is shown in Figure 6a. It can be concluded that the maximum surface settlement is small, about 0.23 m. The continuous advance of LW 1208 does not cause a significant change in the maximum surface settlement. Under current mining conditions, the strata movement within LW 1208 has tended to be stable. As seen in Figure 6b, the maximum surface settlement increases significantly near the goaf mining compared to the solid coal mining stage. Among them, the transition area of solid coal from the face to the goaf is always the first to settle and reaches the maximum amount of settlement, and the settlement rate increases significantly with gradual mining. In summary, after the mining condition of LW 1208 changed from solid coal mining to goaf mining, the strata structure became unstable, and strata movement could easily induce an SMT, such as the \"8.20\" SMT. After the occurrence of the SMT, the surface settlement again increased significantly, indicating that the strata structure is again unstable under the effect of the SMT disturbance, resulting in the rapid surface settlement. Strata structure adjustment also easily induces SMTs, such as the \"8.29\" SMT. The strata structure is extremely unstable after two SMTs, with LW 1208 mining and super-thick strata fracturing again leading to the occurrence of \"12.20\" SMT. Similar to Figure 6a, the surface settlement is basically unchanged along the strike direction of LW 1208, reflecting that the strata structure has reached a stable state (seen in Figure 7a). As seen in Figure 7b, the maximum surface settlement reached 0.24 m as LW 1208 entered the goaf mining stage, which exceeded the maximum surface settlement in the solid coal mining stage. On 31 July 2021, the day before the \"8.20\" SMT, the maximum surface settlement rapidly increased from 0.24 m to 0.38 m. The results show that the super-thick strata are bent and subsided at the goaf mining stage, accumulating a large amount of elastic energy. The \"8.20\" SMT caused the unstable movement of the super-thick strata and induced the \"8.29\" SMT. The maximum surface settlement increased rapidly to 0.48 m. Similarly, before and after the \"12.20\" SMT, the maximum surface settlement showed a two-stage \"stepped\" increasing trend (seen in Figure 7c). Figure 6: Cloud map of surface subsidence evolution during mining of LW 1208.