## 4 Borehole Resistivity Monitoring of Overburden
### Comprehensive Analysis  
#### 4.4.1 Analysis of Development Height of \"Two Zones\" of Overburden  
According to the geological data of the Menkeqing mining area and the indoor rock loading experiment, the overburden type of the test area is medium hard-type rock strata. The failure range of overburden \"two zones\" is estimated by using the \"three regulations\" and the empirical formula summarized by [PERSON] et al. [11]. The maximum \(R_{\text{f}}\) and \(R_{\text{c}}\) obtained by the two formulas are 15 times and 3.2 times, respectively. [PERSON] et al. [9] summarized and analyzed the water-flowing fractured zone and caving zone under similar geological conditions in the Yushenfu mining area. The average \(R_{\text{f}}\) was 26 and the \(R_{\text{c}}\) was 5. At the same time, based on the established three-dimensional mining geological model, the failure and development law of overburden during coal seam 3-1 mining was simulated and measured on site. The results of various research methods are shown in Table 3.  
Table 3 shows that the empirical formula and numerical calculation results are lower than the measured values, and there is a large difference between the empirical formula  
\begin{table}
\begin{tabular}{c c c c c} \hline  & **Empirical** & **Numerical** & **Method of** & **Field Test** \\  & **Formula** & **Simulation** & **Analogy** & **Field Test** \\ \hline \(R_{\text{f}}\) & 15 & 21 & 26 & 24.4 \\ \(R_{\text{c}}\) & 3.2 & & 5 & 5.1 \\ \hline \end{tabular}
\end{table}
Table 3: Contrastive analysis results of “two zones” of overburden.  
and the actual formula. The main reasons for this are as follows: 1 The mining length of the 11-3101 working face is large, the coal seam is thick, and the advancing speed is fast, so the empirical formula is no longer applicable. At the same time, in the simulation calculation, due to the differences between the selection of modeling parameters and the actual conditions, as well as the influence of the later artificial parameter adjustment and other factors, the results also have deviations. 2 The sedimentary history of Jurassic strata is more complex. Compared with the sedimentary environment of the Carboniferous Permian in north China, the thickness of the Quaternary loose layer is larger, composed mainly of aeolian sand and fine sand, and the key layer is located mostly above the middle. However, the empirical formula in the \"three regulations\" is derived mainly from the mining of coal seams under the geological conditions of the Carboniferous Permian coal formation, so there are significant differences. Although the coal seam in the study area is buried shallowly, its coal seam-forming geological environment is consistent with that in the Menkeqing mining area [9]. Therefore, the analogy results have good guiding significance for field measurements, and better illustrate the success of resistivity method in monitoring overburden deformation and failure in coal mining.  
According to the results of numerical simulation and field measurement, the development characteristics of overburden failure in the 3-1 coal seam are comprehensively analyzed. Figure 2 shows that the failure of the surrounding rock mainly takes the form of shear and tensile failure, and the failure area presents a \"saddle\" shape. According to Figures 10 and 11, the actual measured water-flowing fractured zone of borehole #1 in the protective coal pillar area outside the working face is 106 m, while the joint test results of borehole #2 and borehole #3 in the working face reflect that the water-flowing fractured zone is 102 m, indicating that the saddle height of the water-flowing fracture zone is slightly lower than the edge height, which conforms to the \"saddle\" development rule in overburden failure.