"Three Soft" Coal Seam Mining Protective Layer Underlying The Coal Gas Coupling Model And Its Application

In recent years,with the increase of coal mining intensity and mining depth in China,many mining levels have gradually entered the high stress area.Especially in "Three Soft" coal seam(coal seam,floor and roof belongs to soft rock),the intensity and frequency of coal and gas outburst showed an increasing trend.Upper protective layer mining is a preference for regional outburst prevention measures in outburst coal seam group mining.Under the influences of occurrence conditions and exploiting environment of coal-rock seam gas,such as high stress,high gas and soft coal-rock seam,upper protective layer mining is encountering difficulties,e.g.how to improve the outburst prevention effect of the underlying layer and prevent gas abnormal effusing of the protective layer working face as well as many other problems.According to the geological conditions of coal seam gas occurrence in No.4 coal mine of Pingdingshan in Henan Province,a method combining analogue simulation with numerical simulation is used in this paper,and the deformation and pressure relief characteristics of the coal and rock mass under the protective seam mining in the "Three Soft" coal seam are studied systematically,and the law of unloading gas flow is also studied.The application of gas extraction model is also carried out.The main research work of this paper is as follows:(1)A similar experimental study on the permeability evolution of the bottom wall during the upper protective seam mining on the "Three Soft" coal seam was carried out,and the temporal and spatial evolution of movement and deformation of coal seam and permeability was systematically studied.(2)Based on the theory of single porosity media,a gas solid coupling dynamic model of coal deformation and pressure relief gas flow was established based on Poyting-Thomson body creep mechanical model.(3)Based on the multi physical field coupling platform COMSOL Multiphysics,a multi physical field coupling model for mining coal deformation and pressure relief gas flow was constructed,and verified the results of similar simulation tests.(4)Based on the multi physical field coupling platform COMSOL Multiphysics,the application of "Three Soft" coal seam gas bedding drilling drainage and through layer drilling drainage model is carried out respectively,and the gas-solid coupling kinetics model of the coal-rock mass with the flow-based and the gas-solid coupling model based on the creep mechanics model and the traditional linear elastic mechanics model are compared in the application of the model.