Study On Deformation Law Of Coal-rock Mass And The Pressure-relief Gas Extraction Technique Under Upper Protective Layer Mining

In this paper, the combined methods of theoretical analysis, similar simulation test, and field trials are used. The stress distribution characteristic, fracture development Law, permeability variation properties of underlying coal-rock mass, still with the gas flow law of lower protected layer and pressure-relief gas extraction technique under upper protective layer mining are studied systematically. The research has an important significance for safety and efficient production under similar exploitation conditions of low-permeability with high gas and outburst risk coal seam.The stress change mechanical model for underlying coal-rock mass of stope was founded in the paper. Stress formula is derived,combined with the numerical simulation,we obtain the sress change and distribution law of underlying coal-rock mas.We analyze the the deformation law and fracture development characteristics of underlying coal-rock mass movement.with mining proceeding ahead,The total floor coal and rock experiences compression deformation first,then expansion deformation and re-compaction of the continuous periodic destruction.Based on different development characteristics and status of of underlying coal-rock mass,the underlying coal-rock mass under an effect of upper protective layer mining was divided into the floor heave fracture zone and the floor heave deformation zone in this paper. The permability coefficient of change law of underlying the coal seam as follows:The original valueâ†'smally decreasingâ†'increasing greatlyâ†'reducingâ†'stability at last.Transport characteristics on coal seam gas are as follow:desorptionâ†'diffusionâ†'flow. Based on the characteristics, we analyze the crack field in the mining and gas law of the coupling flow field in the paper.The field test for upper protective layer mining of Zhang Ji coal mine of Huai Nan shows that the effect of pressure relief of protected seam is very good. And the maximum swelling deformation quantity of 6th coal seam of protected seam is 16 mm, the maximum swelling deformation rate is 4%, permeability coefficent which increases 660-fold is from 0.054m2/MPa2·d to 35.44m2/MPa2·d. The radius of pressure relief gas extraction of 6 coal mine is 20m. It uses gas extraction technology which is called grid and upwards bores through coal seam at floor strata in protected layer to exhauste and mine pressure relief gas of the protective layer. So the gas extraction rate of the protective layer reaches 44.8%, meanwhile, the residual gas content of under protective layer go down to 2.33m3/t, the residual gas pressure go down to 0.35MPa. All of these show that the effect of pressure relief gas extraction of protected seam is very good and gas quantity of protected seam is effectively reduced. So it eliminate the risk of gas outburst, ensuring safety mining of the protected seam. At the same time, comparative analysis shows the conclusion of the theoretical analysis and Simulation and field test is in good agreement.Figure[50] table[12] reference[80]...