# Study on the \"Two-Zone\" Heights in Lower Slice Mining Under Thick Al Alluvium and Thin Bedrock
## 7 Conclusions  
According to the empirical formula of slice mining in the 'three-underground mining norm' and 'exploration specifications', the height of the overburden caving zone and water  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Two Zones** & **Method** & **Observation Hole 1 \#** & **Observation Hole 2 \#** & **Observation Hole 3 \#** & **Observation Hole 4 \#** & **Result** \\ \hline Height of caving zone/m & Hole peep & 15.26 & \textless{}14.32 & 14.68 & \textless{}14.32 & 15.26 \\ Height of & Leakage & & 53.80–54.45 & & 55.24–55.92 & 55.59 \\ water-conducting & observation & Hole peep & \textgreater{}47.47 & & 55.59 & 55.59 \\ fracture zone/m & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 6: Two zones’ height observation results.  
Figure 17: ‘Two zones’ development height results. (**a**) Development height of caving zone; (**b**) development height of water flowing fractured zone.  
flowing fracture zone after mining in the lower slice working face under the conditions of weak and medium-hard overburden, respectively, is calculated. According to the BP neural network model, it is predicted that the height of the water-conducting fracture zone will be 56.83 m when the mining thickness is 5.8 m. According to the occurrence characteristics of the coal seam in the working face of the no. 1 east panel, the failure height of the overlying strata in the 11092 working face of the lower slice is determined using numerical simulation. The results indicate that with a mining height of 2.5 m for the lower slice and a cumulative mining height of 6 m, the maximum cavity zone height is 15.64 m, and the maximum cavity ratio is 2.61. In layered mining, if the cumulative mining thickness is less than 6 m, the bedrock thickness is at least 30 m, and the clay layer thickness exceeds 5 m, it can be inferred that the clay layer thickness is sufficient to impede the upward progression of the water-conducting fracture zone.  
The height of the cavity zone and water-conducting fracture zone of the 11092 working face in the lower layer was determined using downhole leakage and drilling peep methods. At the cumulative mining thickness of 5.8 m, the cavity zone is 15.26 m, the cavity ratio is 2.62, the water-conducting fracture zone is 55.59 m, and the fracture-mining ratio is 9.58.  
According to the research findings on the fracture development law of overlying strata during the layered mining of the thin bedrock working face at Zhaogu No. 1 Mine, this study can serve as a reference for similar geological production conditions in other working faces.  
Writing--original draft and Investigation, X.L. and H.C.; investigation, X.L.; writing--review & editing, J.J.; formal analysis, W.W.; project administration, J.J. All authors have read and agreed to the published version of the manuscript.  
The work was supported by the National Key R&D Program of China (52174109), Sponsored by Program for Science & Technology Innovation Talents in Universities of Henan Province (23 HASITT011), and Safety Discipline 'Double First-class' Creates Engineering Warehousing Project (AQ20230501).  
The raw data supporting the conclusions of this article will be made available by the authors on request.  
The authors declare no conflicts of interest.