| Coal and gas outburst is one of the worst disasters in coal mine, the implementation of protective mining is effective measures to prevent coal and gas outburst in coal mine with condition. Combined with the elastic-plastic mechanics, rock mechanics, fluid dynamics and related theories, taking the TuZhu upper protective layer's mining as the engineering background, this paper analyzes the stress distribution of the floor strata, movement and deformation and the protected layer's permeability distribution after the upper protective layer's mining, on the basis of which the scope of protection and the gas migration law of the upper protective layer's mining is studied.based on the former,the paper used elastic-plastic mechanics to establish the mechanical model of stope floor and obtained the stress variation,displacement change and protectived layer permeability distribution of stope floor.(1) the place far from goaf where is primitive stress area does not suffer from Mining influence; both ends coal pillar of goaf where is stress concentrated area the stress produced concentration; in a certain range under goaf where is stress decreasing area, the stress is lower, and with work face advancing, the area behind of goaf stress recover gradually. Along with the increase of the lamellar spacing, the influence of mining to floor is dwindled.(2) Analyzed the displacement change of stope floor rock.in the stress concentrated area,the stope floor rock is sinking;in the stress decreasing area, the stope floor rock is heave. The maximal displacement of protected layer under the goaf More than 100mm and Along with the increase of the lamellar spacing the displacement is decreasing.(3) Analyzed the scope of protection of Tu-zhu mine and obtained the fitting curve of the scope of upper protective layer, pointed out that after the exploitation of Tu-zhu coal seam 3, released angle along the strike direction ranged from 39.4°~ 69.8°, the sloping direction was 75.43°or so. (4) Obtained the distribution of permeability in Tu-zhu coal seam 5 through the relationship between stress and permeability, and analyzed the gas flow channel.FLAC3D software and COMSOL software were used to simulate the surrounding rock stress and displacement variation and gas migration during the protection layer mining of Tu-zhu mine.(1) Simulate the displacement variation of stress and stress distribution under the floor when mining the upper protective layers. based on the displacement variation of stress and stress distribution under the floor, delineated the released angle, in the direction of trend, the released angle range from 52.36°~61.89°; in the sloping direction, the released angle of lower is 73.2°, the released angle of top is 74°(2) Simulate the Tu-zhu mine upper protective layer of during the mining, and gas migration law in protective layer. Exploitation of 20m, the minimum gas pressure in protective layer was reduced to 1.125MPa; exploitation of 40m, the minimum gas pressure in protective layer was reduced to 0.65MPa; excavation of 60m, the minimum gas pressure in protective layer was reduced to 0.5MPa.According to the actual situation of TuZhu coal mine, the paper designs the observation program of the TuZhu upper protective layer's mining, analyzes the protective layer, the protected layer's stress and change law of the gas pressure in the process of 3 coal mining, and designates the protection range that along the alignment the relief angle is 53.7°~ 65°and along the slope the relief angle is 74.9°around. With the comparison of the theoretical analysis and the numerical simulation, it is shown that the results are consistent. this laid a foundation for using methods of theoretical and numerical to predict protective effect of coal and gas outburst mines in the future. |
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