# Study on the Co-Evolution Mechanism of Key Strata and Mining Fissures in Shallow Coal Seam Mining
## 6 Conclusions  
1. Through the monitoring of the development characteristics of surface mining fissures during the mining process, it was found that the periodic fissures in the mining face of the shallow coal seam were in the shape of \"C\", and the boundary fissures were in the shape of \"(\". The maximum mining fissure position was the same as the advanced mining fissure position of the working face, with a high degree of overlap, being a reflection of mining fissures during different mining periods.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **Soil Layer** \\ **Related** \\ **Parameters** \\ \end{tabular} } & \multirow{2}{*}{**Average Bulk**} & \multirow{2}{*}{**Poisson Ratio**} & \multirow{2}{*}{\begin{tabular}{c} **Cohesion** \\ **(MPa)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Angle of** \\ **Internal** \\ **Friction (°)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Elastic** \\ **Modulus** \\ **(MPa)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Critical Tensile** \\ **Deformation of Ground** \\ **Surface (mm/m)** \\ \end{tabular} } \\ \cline{2-6}  & 23 & 0.35 & 0.077 & 36 & 32.45 & \(-\)0.003 \\ \hline \multirow{2}{*}{\begin{tabular}{c} **Related** \\ **parameters** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Average Bulk** \\ **Density** \\ **(kN/m°)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Fracture Angle** \\ **of Rock** \\ **Statum (°)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Cohesion** \\ **Internal** \\ **Friction (°)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Angle of** \\ **Depth of Key** \\ **Stata (m)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Buried** \\ **Depth of Key** \\ **Stata (m)** \\ \end{tabular} } \\ \cline{2-6}  & 26 & 68 & 1.2 & 37 & 54.89 & / \\ \hline \hline \end{tabular}
\end{table}
Table 3: The occurrence characteristic parameters of rock and soil layers in Hanjiawan Coal Mine.  
Based on the fracture characteristics of the key strata and the stress distribution pattern, it can be concluded that the overlying rock and soil layer on the key strata of the working face formed up and down type I-I mining fissures and type I-II mining fissures, and the rotation of the key blocks resulted in mining fissures. The dynamic fissures experienced five dynamic activation processes, namely, generation, expansion, closure, generation, and re-closure, and the calculation formula for the dynamic periodic evolution of the mining fissures was obtained.
3. Through the study of the fissure propagation characteristics, the calculation expression of the influence of the rock-soil layer load and the fracture distance of the rock formation on the mining fissure propagation was obtained. According to the control function of the key strata on the overlying strata and the geological occurrence characteristics, the overall fracture angle \(\beta_{Z}\) of the strata and the lagging distance \(L_{Z}\) of the mining fissures were 36.84 m.
4. According to the stress distribution characteristics of mining up and down type I-I and type I-II mining fissures in the working face, the formula for calculating the dynamic evolution depth of mining fissures was obtained, and the discriminant formula for the penetration of up and down mining fissures was proposed.
5. According to theoretical calculations and on-site drilling measurements, it was found that the up-and-down type I-I mining fissures in Hanjiawan Coal Mine No.2-2 coal mining did not penetrate, and the type I-II mining fissures penetrated. The heights of fissure development were 44.38 m and 98.35 m, and the penetrated fissures easily formed sudden disasters such as water inrush, sand inrush, and air leakage.