The Height of Fractured Zones Caused by Strip Wongawilli Mining in a Shallow Buried Coal Seam Underlying a Hard Roof

The exact determination of the height of fractured zones in overlying sedimentary strata is important in coal mining performed underneath water bodies and for a safe production. To prevent the inrush of water and sand during strip Wongawilli mining, we studied the height of fractured zones in shallow coal seams underlying a hard roof. Based on the geological setting and mining conditions at the Zhaowu coal mine, the height of the fractured zones in overlying strata was measured using the loss of drilling fluid method and by numerical simulation. The height of the fractured zones and its development characteristics during strip Wongawilli mining in shallow buried coal seam underlying a hard roof were obtained. The results demonstrate that the disturbance of the overlying strata during strip Wongawilli mining is reduced and the height of the fractured zones is smaller relative to that occurring during critical mining. The height of fractured zones increases with mining width in a steppedfinger line, and it manifests stable in each stage, but turns into the next stage by sudden increase. The existing method of calculation and the traditional empirical formula to obtain the height of the fractured zones are not suitable for strip Wongawilli mining. The calculation should be based on the size of mining.