## 5 Numerical Simulation Analyses of the Dynamic Evolution Process of Overlying Rock Strata
### Analysis of the Development Process of Overlying Rock Strata  
When excavating the first step, that is, advancing the working face by 20 m, there was no collapse of the roof overlying rock. When excavating the second step, that is, advancing the working face to 40 m, as shown in Figure 6a, the roof rock layer is exposed. Under the influence of gravity, the bent rock beam hangs to a certain span. After the bending settlement reaches the critical strength, a separation space appears between the first and second layers, namely between the Yan'an group of carbonaceous mudstone and the Yan'an group of coarse sandstone, with a separation space length of about 5 m. Some immediate roof collapses, with a collapse height of about 9.8 m, and the collapsed rock layer covers the entire goal. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Rock Name** & **Density** & **Bulk Modulus** & **Shear Modulus** & **Friction** & **Cohesion** & **Tensile Strength** \\  & **(kg/m\({}^{3}\))** & **(GPa)** & **(GPa)** & **(\({}^{\circ}\))** & **(MPa)** & **(MPa)** \\ \hline Gravel rock & 2600 & 9.50 & 6.05 & 59.40 & 1.54 & 0.67 \\ Mudstone & 2590 & 0.98 & 0.55 & 45.56 & 0.98 & 0.58 \\ Sandy mudstone & 2510 & 0.55 & 0.32 & 45.88 & 0.29 & 0.40 \\ Medium grained sandstone & 2420 & 7.38 & 4.43 & 58.40 & 0.78 & 0.61 \\ Silstone & 2480 & 2.00 & 0.62 & 46.90 & 0.56 & 0.25 \\ Coarse sandstone & 2490 & 0.35 & 0.33 & 59.40 & 0.46 & 0.33 \\ Carbonaceous Mudstone & 2480 & 0.60 & 0.34 & 45.56 & 1.06 & 0.40 \\ No. 3 coal & 1380 & 0.75 & 0.52 & 39.45 & 0.30 & 0.12 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Parameters summary table of the Guojiahe coal mine rock mechanics. Figure 5: Working face 1304 numerical simulation model. In Figure 5(b), when excavating in the 5 th step, that is, when the mining length reaches 100 m, the pressure on the overlying strata becomes more intense. Breakage occurs at both ends and the middle part at a distance of about 45 m above the top of the coal seam, exhibiting a combined movement and forming a separated space between the overlying strata above. The maximum height of the space is about 0.6 m. At this time, the fissure water in the 4 th layer of overlying strata will flow into the goal; however, since the water-conducting fissures will develop through the separated space in a short period of time, the amount of accumulated water in the space is not large. The water inflow situation does not have the characteristics of rapidity, large instantaneous water volume, difficult to control, etc. When excavating in the 6 th step, as shown in Figure 5(c), with an excavation length of 120 m, the separation space rapidly develops upwards. As the separation space between the 3 rd and 4 th layers gradually closes, the separation space between the 6 th and 7 th layers begins to appear and gradually increases. In Figure 5(d), when excavating to the 8 th step, i.e., with a mining length of 160 m, the separation space between the 6 th and 7 th layers, that is, the separation space between the Anding Formation sandy mudstone and the mudstone of the Anding Formation reaches its maximum The maximum width of the space is about 15 m, with a height of approximately 1 m, located 130 m from the top of the coal seam. The collapsed rock mass and the goat exhibit a trapezoidal structure, with a collapse angle of 66\({}^{\circ}\). In Figure 5(e), the excavation reaches 200 m, and, for the first time a separation space appears between the 8 th impermeable rock layer and the 9 th aquifer layer, which may become a water storage space. By 220 m of excavation, as shown in Figure 5(f), the separation space between the 8 th and 9 th layers reaches its maximum development. At this point, the maximum width of the space is about 22 m, and the height is approximately 0.9 m.  
When the excavation length reaches 240 m, a second separation space is formed between the 8 th and 9 th layers in the direction of the advancing working face, and continues to develop with ongoing mining.