## 3 Results and Discussion
### Analysis of Ground Surface Subsidence  
Due to its special geological conditions, with a shallow burial depth and weak rock strength, when the working face is advanced to 80 m, the overlying rock strata are affected by mining activities, and the movement of the rock strata spreads to the ground surface. At this moment, the amount of subsidence is small and not obvious. As the working face continues to advance, the overlying rock strata above the goal lose their original support, and the stress equilibrium state is broken. Figure 8 is a schematic diagram of the ground surface subsidence. Under the action of gravity, the overlying rock strata begin to move and deform towards the goal. Due to the different mechanical properties and thicknesses of the key stratum and the lower rock strata, during the movement of the rock strata, relative displacements and uncoordinated bending deformations occur between adjacent strata, resulting in the generation of separation cracks between the key stratum and the lower rock strata and the emergence of a caving and subsidence space. After the key stratum breaks, the upper rock strata it bears also cave in and subside accordingly until it affects the ground surface, and an obvious subsidence basin appears on the ground surface, with the maximum subsidence value being 4.57 m.  
As can be seen from Figure 9, starting from when the working face is advanced to 80 m until the end of the working face mining, the maximum subsidence value of the ground  
Figure 8: Surface subsidence diagram. surface steadily increases in the early and middle stages and gradually stabilizes in the later stage. Certainly, for the phenomenon of overburden subsidence caused by mining activities, the value of overburden subsidence can also be calculated through formulas, which can, to a certain extent, predict the disasters of ground surface damage and subsidence. This formula integrates the ideas of the stratification method, the probability integral method, and the curve method. It is assumed that under the conditions of multi-seam coalmining or complex geological conditions, for the ground surface subsidence value at a certain coordinate point \((x,y)\), it is \(W_{t}\), based on the idea of the stratified summation method, and represents the sum of the ground surface subsidence values caused by each stratum or various factors [21]:  
\[W_{t}=\sum_{i=1}^{n}W_{i} \tag{11}\]  
For the ground surface subsidence value \(W_{j}\) of each layer \(i\), integrate the probability integral method and the curve method, then \(W_{i}\) can be expressed as  
\[W_{i}=W_{\text{max}i}\times F_{i}(x,y) \tag{12}\]  
Here, \(W_{\text{max}i}=m_{i}\times q_{i}\times\cos\alpha_{i}\), \(m_{i}\) represents the mining thickness of the coal seam, \(q_{i}\) is the subsidence coefficient, and \(\alpha\) is the dip angle of the coal seam. \(F_{i}(x,y)\) is the comprehensive influence coefficient. Then it follows that  
\[F_{i}(x,y)=\omega_{i}\cdot e^{-\pi(\frac{x^{2}}{\tau_{i}^{2}}+\frac{y^{2}}{ \tau_{i}^{2}})}+(1-\omega_{i})\cdot f_{i}(x) \tag{13}\]  
Therefore, the surface subsidence value is  
\[W_{t}=\sum_{i=1}^{n}m_{i}\cdot q_{i}\cdot\cos\alpha_{i}\cdot\left[\omega_{i} \cdot e^{-\pi(\frac{x^{2}}{\tau_{i}^{2}}+\frac{y^{2}}{\tau_{i}^{2}})}+(1- \omega_{i})\cdot f_{i}(x)\right] \tag{14}\]  
Here, \(\omega_{i}\) is the weight coefficient, and the value range is \([0,1]\). In the region where the geological conditions are relatively uniform, that is, the lithology, mechanical properties, etc., within the mining area change slightly, and the dip angle of the coal seam is small (\(\alpha\leq 15^{\circ}\)), a relatively large value can be taken for \(\omega_{i}\). When the geological conditions in the mining area are relatively stable, and the geological conditions of the predicted area  
Figure 9: Dynamic evolution diagram of maximum surface subsidence value. are similar to those of the measured data on which the existing typical curves are based, a relatively small value can be taken for \(\omega_{i}\).