Characteristics of overlying rock mining failure and evaluation of water - sand controlling performance in thin bedrock areas

Aiming at the problem of water and sand collapse during mining under the near loose aquifer in the exposed area of shallow coal seams, and taking the 3_I126 working face of Luxi Coal Mine as the engineering background, a combination of physical simulation, numerical simulation, and on-site measurement was used to study the characteristics of overlying rock failure and the height of water conducting fracture zone in this working face. Based on the clay layer, wind oxidation zone, and protective layer, the evaluation criteria and the performance evaluation system for the key strata of water-sand controlling have been established. Combined with the ratio of the field measured height of fractured zone to mining height, the height of water conducting fracture zone under different mining height has been predicted, and then the limited height mining plan under different bedrock thickness conditions has been determined. The results show that under the condition of 3.5 m mining height, the height of water conducting fracture zone is 43.5 and 46.5 m, and the ratio of the height of fractured zone to mining height is 12.43 and 13.29 in physical simulation and numerical simulation, while the field height of water conducting fracture zone is 41.51 m and the ratio of the height of fractured zone to mining height is 11.86 in field measurement. The overlying clay layer and wind oxidation zone on the 3_I126 working face have high water-sand controlling performance, the main factor affecting safe mining is the water-sand controlling performance of the protective layer, which mainly depends on the ratio of remaining bedrock thickness to mining height. The segmented limited height mining plan under different bedrock thicknesses provides a theoretical basis for increasing the mining limit and preventing water hazard in the loose aquifer at the bottom of the Cenozoic.