Research On Pressure Relief Mechanism And Application Of Repeated Mining Of Upper Protective Layer Of Coal Seam Group

In order to reveal the pressure relief mechanism under the condition of repeated mining of the upper protective layer of the coal seam group,this paper adopts the research methods such as theoretical analysis,similar simulation,numerical simulation and field test to analyze the evolution and movement of the fissures of the surrounding rock in the stope after the repeated mining of the upper protective layer.The laws of deformation and stress distribution are systematically studied.The specific research results are as follows:(1)Qualitative and quantitative analysis was carried out on the failure characteristics of the overlying rock under the repeated mining of the upper protective layer;three failure characteristics of the floor strata under repeated mining conditions were analyzed;different mechanical models were used to analyze the different key layers The floor stress distribution of the structure.(2)Through similar simulation and numerical simulation experiments,the damage,deformation and stress distribution law of surrounding rock under repeated mining conditions were analyzed.The evolution process of the compaction and closure of the fissures in the middle of the overlying rock,the coal strata on the floor of the goaf has undergone the deformation process of compression→expansion→recovery,and the surrounding rock stress in the stope has experienced the process of increase→decrease→recovery.Crack strips are formed on both sides of the floor of the zone.When the lower protective layer was mined,the surrounding rock of the stope experienced a similar disturbance process again,and the continuity and depth of the fracture development in the floor increased.(3)By carrying out engineering field tests in a certain mine of Pingmei,,the pressure relief effect of the protected layer after repeated mining was investigated,and the reliability of theoretical analysis,similar simulation and numerical simulation was verified.,the gas pressure decreased by 69.7%,the gas content decreased by 44.5%,the gas outflow increased by 29.8%,and the expansion deformation increased from5 mm to 7mm.