Development Patterns of Fractured Water-Conducting Zones in Longwall Mining of Thick Coal Seams-A Case Study on Safe Mining Under the Zhuozhang River

The key to the safe mining of thick coal seams under rivers is understanding the development patterns of fractured water-conducting zones (FWCZ) when various mining methods are used. To solve this problem, we employed numerical simulation to investigate FWCZ when slice mining and longwall caving mining are performed. When slice mining was carried out, the maximum height of the FWCZ in the higher slice was 88 m. When the lower slice was mined, the maximum height became 95 m, and the ratio of the fracture height to the coal seam thickness was 15.8. For longwall caving mining, the height of the FWCZ reached 126 m, which was 31 m more than that of slice mining, and the ratio of the fracture height to the coal seam thickness was 21. Through field measurements, the height of the FWCZ during longwall caving mining of thick coal seams was verified. The measured height was 108.87-112.57 m, and the measured ratio was 19.08-19.28. Under the same stratigraphic conditions, changes in the bulking factor and structural stability of key strata were the dominant factors that determined how mining methods affected the height of the FWCZ. These development patterns can provide significant theoretical insights for effectively preventing water hazards on mine roofs.