Microseismic test and numerical simulation analysis of floor failure depth of isolated coal mining face

Aiming at the damage of coal seam floor caused by mining in isolated coal mining face, taking 11913 isolated coal mining face in Gequan coal mine of Hebei Province as the research object, and using KJ959 coal mine microseismic monitoring system to detect the floor failure depth. It is recognized that the microseismic events mainly occur in the roadway of the isolated coal mining face during the mining process, and the maximum vertical failure depth is about 20~25m; Moreover, using the COMSOL multi-physical field numerical simulation platform, the variation of in-situ stress and failure law of coal seam floor under the conditions of 11912 first coal mining face, 11914 jumping coal mining face and 11913 isolated coal mining face are analyzed. The simulation results show that the in-situ stress concentration state of coal pillars under the conditions of 11912 first mining face or 11914 jumping mining face has little change, and the maximum failure depth is less than 11.56 m, which only develops into the interior of grouting reformation layer. Under the condition of 11913 isolated mining face, the in-situ stress concentration state of coal pillars on both sides of mining face increases sharply due to the influence of repeated mining in mining faces 11912 and 11914, and the maximum failure depth increases to 23 m, which has extended to Benxi limestone aquifer of coal seam floor. The conclusion has certain reference value for the study of floor failure law of North China type coalfield and the selection of grouting transformation horizon under different mining conditions.