In order to improve effectiveness, safety and economy of protection layer mining, elasto damage constitutive model of coal and rock mass was constructed based on Mole-Coulomb criterion. Using damage variable as transition, coal and rock mass permeability-damage evolution equation was also built. Then, using mining rock mechanics, percolation mechanics and damage mechanics, gas seepage-stress-damage coupling model of mining coal and rock was constructed. And the elasto plastic damage constitutive model was verified by numerical simulation program through FLAC3D. At last, gas seepage behavior under long distance protective later mining in Gu Qiao Coal Mine was studied through the elasto plastic damage constitutive model. Results showed that under influence of mining, permeability coefficient of protected seam was 1760 times of the original value and gas pressure deduced from 2.8 MPa to 0.6 MPa. Coal and gas outburst hazard was eliminated. Numerical simulation results were basically consistent with actual situation which indicated that the elasto damage constitutive model and gas seepage-stress-damage coupling model can be used to describe coal seam damage and its permeability change. This result has guiding significance on feasibility of protection layer mining, effect pre-evaluation of pressure relief gas extraction in protected seam and optimization of pressure relief gas extraction technology.
Protection layer mining and gas extraction in pressure releasing area of protected seam are the most effective, economic and reliable outburst prevention technique. They are also compulsory and prior method for coal seams with outburst danger in national regulation (Cheng et al. 2003, Chen et al. 2004, State Administration of Coal Mine Safety 2009, Yu et al. 2004). Tang Chunan, Liu Hong-yong and Wang Deng-ke have built damage constitutive model of coal and rock mass (Liu et al. 2010, Wang et al. 2010, Yang et al. 2005, Yang et al. 2001). They studied evolution behavior between stress, damage and permeability evolution during coal mass deformation under protection layer mining. The achievement provides basis for study on coal mass deformation behavior and gas seepage behavior under protection layer mining.