## 4 Structural Control Mechanisms on Coal and Gas Occurrence in Mines
### Stepwise Structural Control of Gas Occurrence
#### 4.2.3 Structural Control of Gas Occurrence at the Turning End of the Kaiping Syncline  
Based on the available measured data for predicting gas content distribution at the turning end, the gas occurrence zones are classified into low gas content zones (\(<\)4 m\({}^{3}\)/t), medium gas content zones (4-8 m\({}^{3}\)/t), and high gas content zones (\(>\)8 m\({}^{3}\)/t). According to the gas content distribution maps, high-gas zones in the No. 7, No. 9, and No. 12 coal seams are primarily located on the northwest limb of the Kaiping syncline in the southern part of the Zhaoegzhuang mine. Only a tiny portion of the high-gas zones in the No. 12 seam are found on the southeast limb, near the core of the Kaiping syncline. Among the seams, the No. 12 coal seam has the largest high-gas zone, while the No. 7 seam has the smallest. The distribution of medium- and low-gas zones in the No. 9 and No. 12 coal seams follows a clear pattern, with these zones covering almost the entire southeast limb of the turning end. Moving toward the northwest limb, the coverage area decreases, with low-gas zones primarily located in shallow areas (Figure 10). In terms of geological structure, the northwest limb of the turning end, where the Zhaoegzhuang mine is located, is subjected to compressional stress from the northwest direction, forming several medium- to large-scale transgressional faults. The mine is predominantly characterized by fault development, with the western limb experiencing the most significant compression and the most developed reverse faults. The effect of this compression diminishes toward the east, where the eastern limb near the core of the Kaiping syncline has fewer faults. In the study area, the buffering effect of the syncline has prevented the northwest-directed tectonic stress field from impacting the Linxi mine. Fault development in the Linxi mine is limited, primarily occurring in the northern part of the mine. The northern compressional stress field, caused by the twisting of the Kaiping syncline's axis, has led to the formation of a series of NWW-oriented folds within the Linxi mine. According to the collected and analyzed fault data (Table 1), the Zhaoegzhuang mine predominantly features reverse faults, with a total of 13 reverse faults and 11 normal faults. In contrast, the Linxi mine primarily has normal faults, with 10 normal faults and 3 reverse faults. Figure 9: Schematic diagram of gas distribution in the Kaiping Xiangxi mine. In mining areas, the structural characteristics of the mining field are the primary control factor for gas occurrence. The sealing capacity of the geological structure directly influences gas occurrence, and different structural features (such as folds, faults, and igneous intrusions) lead to variations in gas occurrence (Figure 11). In the eastern limb of the Zhaogezhuang mine, structural development is less pronounced, the dip angles of the strata are smaller, and they are close to the axis of the Kaiping syncline. At the same burial depth, gas content is relatively low. In the wide syncline near the wellhead, where fault structures are densely developed, gas content and its variation gradient are high at the same burial depth. There is a lack of geological data for the western limb of the mine, but based on the structural stress field trend, tectonic activity in the west is more substantial than in the central and eastern parts, with many reverse faults. This impedes gas dissipation, leading to the hypothesis that gas content and pressure are both higher in the western region (Figure 11a). In the southern limb of the turning end, extensional faults are well developed in the northern part of the Linxi mine, near the end of the Kaiping syncline, which promotes gas dissipation, resulting in lower gas content. Moving south toward the monocline zone, Dujunzhuang Anticline zone, and Heiyazi Syncline zone, gas content tends to increase at the same burial depth. In the Heiyazi Syncline zone, where the