Research on Floor Failure Features of Coal Seam above the Confined Aquifer in The Case of Backfill Mining

Abstract

Water inrush accident is one of the most common disasters in the production process of coal mines, while coal mining in deep strata has always suffered from the threat of the confined aquifer. It is of great significance for mining safety assessment and water inrush prevention to grasp the failure features of coal seam floor during the mining. The article adopted the methods of numerical simulation and field test to make a comprehensive study on floor failure characteristics of 7# coal seam above confined aquifer in M coal mine in the case of backfill mining. Numerical simulation results of FLAC3D software showed that the backfill mining had reduced the pressure relief area, the working face floor-heave and the stress concentration of the surrounding rocks, so that the failure depth of the floor did not develop along with the advancing of working face. Meanwhile, water injection tests on the total 9 testing sections of two drills of the coal floor rocks indicated that during the working face advancing, the amount of water leakage of testing sections above 16.8m has significantly increased, and when the working face was far away from the testing point, the leakage would still be higher than that before mining and in a certain extent the rock stratum had been damaged. But water leakage of testing sections of 16.8-25.5m appeared no obvious change, which showed that the rocks kept the original state without being destroyed during the mining. Finally, it is seen that the results of field test and numerical simulation were basically the same that is in the case of backfill mining, the depth of floor rock failure of 7# coal seam was about 16m and there was no danger of water bursting.