Development Patterns of Fractured Water-Conducting Zones under Fully Mechanized Mining in Wet-Collapsible Loess Area

The development pattern of fractured water-conducting zones (FWCZs) is closely related to mining safety and water conservation in mining areas. However, neither the development pattern nor the empirical formula in the prediction of the height of FWCZs are clear for fully mechanized caving mining conditions in wet collapsible loess areas. We took Lu’an Coal Mine as a case study, employing field measurements and numerical simulation to investigate surface subsidence and FWCZs. Under the conditions of fully mechanized top coal caving in thick coal seams, surface movement is more intense, and surface cracking is more frequent. Field measurements using boreholes indicated the ratio of fracture height to coal seam thickness was 19.1–23.4, and thethe ratio stays stable both by sliced fully mechanized mining and fully mechanized mining. The height of the FWCZ with fully mechanized mining is 1.37 times and 2.31 times larger than the height with sliced fully mechanized mining and ordinary mining, respectively. The numerical simulation by RFPA illustrated that the height of the FWCZ remained stable when it reached a certain rock level with the working face moving forward. Furthermore, we developed an empirical formula for predicating the maximum height of an FWCZ under fully mechanized mining conditions in wet collapsible loess areas. Finally, the research findings were applied in several coal mines to achieve safe production and water conservation. This work provides guidance for effectively mining safely and water conservation in similar geographic conditions.