Researches on mining rock failure process and gas flow with upper protective layer extraction

Mined fracture is the passage of gas flow, and gas flow law is the precondition of control gas disaster. Field test and laboratory analog model test on the stress-relief effects of protective layer extraction are time-consuming and laborious. Based on the rock heterogeneity and coupled gas-solid interaction between gas permeability and rock damage, considering geologic condition and excavation technique at Pingdingshan Mine No.5, a numerical model is established with the gas-solid coupling rock failure process analysis system RFPA-Gas to simulate the stress variation law, roof and floor deformation, fracture evolution law, displacement in the protected layer, varying gas permeability and gas flow law during upper protective layer extraction. The simulation results reproduced stress variations in coal and rock strata, roof and floor deformation and fracture evolution process. It showed that stress relief occurred in the protected layer, which led to vertical and horizontal displacements, significant increase of about 2500 times in gas permeability, gas desorption and migration. Hence, the outburst threat in the protected layer was eliminated. The simulation results are in good agreement with the stress-relief effects in field.