Numerical Simulation And Study On Gas Drainage From Boreholes In Xie-yi Coal Mine Under Upper Protective Layer Mining

Formation and evolution of fracture in coal and rock mass in the process of pressure relief in drilling or protective layer mining is the development and accumulation process of the damage,and the flow of gas in the damaged coal and rock mass is a complex process of mutual coupling between gas migration and coal seam deformation.On the basis of the rock mechanics,damage mechanics and seepage mechanics,it improves the effective stress of Terzaghi considering the damage,derives the damage evolution equation and the elastoplastic damage constitutive equation with the strain as the internal variable,and establishs the coal permeability equation;Solid gas dynamic coupling model of coal containing gas with seepage-stress-damage is established.This paper studies and analyzes the law of gas drainage in the C13 coal seam in the experimentation area,And compared with the field engineering practice to verify the feasibility of numerical analysis.To sum up,the main conclusions of this paper are as follows:Based on the characteristics of Xieyi coal mine outburst and gas geological law,Thanks to the superior protective layer mining conditions,the protective seam mining strategy is carried out,and the pressure relief gas drainage of C13 coal seam can be fundamentally changed.The pore structure characteristics of coal and gas outburst coal seams in Huainan area was double "S" shape,adsorption constant b <0.5MPa-1 by macroscopic and microscopic analysis..Through the analysis of the model,the protective layer is formed,and the pressure relief zone is formed in the coal seam of the top(bottom)of the goaf.The stress concentration is formed on the front of the working face and at the outside of the opening.The pressure relief range increases,and the pressure relief area increases,and at the same time,the stress concentration zone of the protective coal seam moves forward.When the working surface is more than 100 m,the maximum expansion rate in the expanded zone of the protective layer reaches 3.2 ‰,and the expansion zone is maintained and gradually transferred to the working face.the compression ratio of the compaction zone gradually reaches 1.3 ‰.With the continuous drainage,the scope of the impact of mining gas gradually expanded,the gas pressure around the borehole decreased further,The gas is further desorbed,the equivalent stress of the coal seam is reduced,the coal seam iscompacted,its permeability is gradually weakened,the drilling and drainage rate is gradually reduced,and finally stabilized.After 150 days,the gas extraction rate is close to 27L/min,and the effective drainage radius is nearly 2m.The engineering practice shows that: With the advancement of the working surface of the protective layer,the maximum relative expansion of the C13 coal seam in the relief zone was 4 ‰;The average flow rate of single hole is gradually increased,and the maximum value is 22.0156 L / min.The average flow rate of single hole in the north section is 1.157 ~ 2.083 L / min.