# An FDM-Based Dynamic Zoning Method for Disturbed Rock Masses above a Longwall Mining Panel
## 5 Conclusions  
This paper proposes an FDM-based dynamic zoning method for disturbed rock masses above a longwall mining panel. This method is mainly composed of four stages: (1) establishing a simplified complete stress-strain curve; (2) determining the zoning criteria; (3) adaptively adjusting the mechanical parameters of the disturbed rock mass; and (4) numerically modeling the longwall mining based on the FDM.  
To demonstrate the effectiveness, the proposed method has been applied to simulate underground mining in the Taixi coal mine. It has been concluded that (1) the coal-seam roof above the mined-out area does not fall immediately with the advancing of the excavation face but caves periodically; (2) the \"four zones\" of overlying strata are dynamically developed during the mining process and are strongly related to the roof-caving process; and (3) during the mining process, there is a high probability that the fissures in the fractured zone at the south side of the panel would connect with the fissures in the surface cracking zone, which needs careful attention and specific treatments (for example, by bulldozer rolling) in the actual longwall mining process.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Mining Area** & **Thickness (m)** & \begin{tabular}{c} **Dip Angle** \\ **(o)** \\ \end{tabular} & **Mining Method** & \begin{tabular}{c} \(\sigma_{\text{c-average}}\)* \\ **(MPa)** \\ \end{tabular} & \begin{tabular}{c} **Subsidence** \\ **Coefficient** \\ \end{tabular} \\ \hline Fengfeng & \begin{tabular}{c} 0.8 \\ 2.4 \\ 1.9 \\ \end{tabular} & \begin{tabular}{c} 19 \\ 11 \\ \end{tabular} & Longwall & \begin{tabular}{c} 47.7 \\ 57.9 \\ \end{tabular} & \begin{tabular}{c} 0.78 \\ 0.84 \\ \end{tabular} \\ \hline Zazohuang & \begin{tabular}{c} 1.5 \\ 1.9 \\ \end{tabular} & \begin{tabular}{c} 24 \\ 4 \\ \end{tabular} & Longwall & - & \begin{tabular}{c} 0.88 \\ 0.78 \\ \end{tabular} \\ \hline Yanzhou & \begin{tabular}{c} 7.8 \\ 8.2 \\ \end{tabular} & \begin{tabular}{c} 4 \\ 4.3 \\ \end{tabular} & \begin{tabular}{c} Fully \\ mechanized cing \\ \end{tabular} & \
\begin{tabular}{c} 23.1 \\ 13 \\ \end{tabular} &
\begin{tabular}{c} 0.81 \\ 0.84 \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table}
Table 2: The measured subsidence coefficients of neighboring coal mines.  
The numerical simulation results obtained in this work, such as the periodic caving of coal-seam roof and the dynamic development characteristics of the four zones, are consistent with the observed distribution and other research results. This indicates that the proposed dynamic zoning method is capable of effectively analyzing and predicting the dynamic development characteristics of the four zones.  
In the proposed method, only the cohesion and the internal friction angle of disturbed rock masses are adjusted during the longwall mining process. Future work will be focused on estimating and adjusting the elastic modulus and Poisson's ratio of disturbed rock masses.  
Conceptualization, S.J.; methodology, S.J.; validation, K.Z.; formal analysis, K.Z.; writing--original draft preparation, K.Z.; writing--review and editing, K.Z.; supervision, S.J.; project administration, S.J.; funding acquisition, S.J. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China, grant number 42230709, 41772326.  
Not applicable.  
The authors declare no conflict of interest.