Safety evaluation of repeated mining in large mining height working face under surface water body
In order to determine the feasibility and safety of repeated mining in working face with large mining height under surface water body,FLAC3D numerical model was used to study the failure law of overlying strata after repeated mining of No.5 coal and No.8 coal in Hongshiwan Coal Mine of Ningdong Coalfield.The working faces of No.5 coal and No.8 coal were both large mining height working faces,and the mining heights were 4.6 m and 4.8 m,respectively.According to the numerical simulation results,the heights of caving zones after mining of No.5 coal and No.8 coal working faces were 13.8 m and 15.0 m,respectively.The height of water conduction fracture zone of No.8 coal working face was 242.0 m,and the thickness of protective zone was 56.4 m.The shallowest part of No.8 coal working face was 353.0 m away from the surface water body,which was greater than the height of the waterproof coal(rock)pillar(298.4 m).Combined with the structural development conditions of the study area and the water-resisting performance characteristics of the aquifuge,it was determined that the safety of repeated mining of the large mining height working face of No.5 coal and No.8 coal under the surface water body was high.The results showed that the numerical model could be used to analyze the failure law of overburden rock after repeated mining of large mining height working face.Through case analysis,the safety evaluation of repeated mining of large mining height working face under surface water body was in line with the actual situation,which could be used by field as the basis for evaluating the threat degree of working face by surface water body in the future.
surface water bodylarge mining height working facewater conduction fracture zonenumerical simulationrepeated mining
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