Abstract:

Mined fracture is the passage of gas flow, and gas flow law is the precondition of control gas disaster. Based on the dynamic failure process and coupled fluid-solid interaction between gas flow and solid deformation, considering geologic condition and excavating technique in Mine No. 5 in Pingdingshan, a numerical simulation 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 seam, change in 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 during protective layer extraction. The movement of rock strata were characterized by upper three zones and lower two zones: caving zone, fracture zone and bending subsidence zone in the vertical direction in the overlying stratum; floor deformation and failure zone and elasto-plastic deformation zone in the vertical direction in the underlying stratum. The gas flux, gas pressure and gas permeability change with the upper protective extraction. And the gas permeability of protected coal seam dramatically increases about 2 500 times. The tensile-shear gas flow passages appear under the pillar between compression zone and expansion zone. The gas flow speed and the flux reduce at the stress-concentration zone. The expansion zone is composed of stress relief and sudden expansion zone and stress relief and steady expansion zone. The gas flow speed and the flux increase dramatically at stress relief and sudden expansion zone. The gas flow speed and the flux increase slowly at stress relief and steady expansion zone. The gas outburst often occurs at stress relief and sudden expansion zone. The results provide a clear direction for gas control in the protective layer. The simulation results are in good agreement with the stress-relief effects in field.

Key words: upper protective layer, mined fracture, gas flow and migration, stress distribution, numerical analysis