Study On Gas Migration Rule Under The Influence Of Mining In Low Permeability Thick Coal Seam And The Response Mechanism Of “Replacing Roadway With Pore” And Application

When mining high-gas and low-permeability coal seams,the amount of gas gushing out from the stope is large,and local gas accumulation is serious.It is difficult to meet the relevant requirements by relying on the existing wind exhaust and drainage technology,so it is very important to reveal the gas migration law in the stope under the influence of mining and establish the "replacing the tunnel with the hole" gas control system.Prevention and control of gas disasters and avoiding the discharge of gas into the atmosphere play a key role.Taking the 2-105 working face of Tenghui Mine as the background,using theoretical derivation,numerical simulation and other means to discuss the overlying coal and rock mass cracks,displacement evolution law and stope stress redistribution mechanism when mining thick coal seams from a macro perspective,the results show that,The subsidence displacement of the overlying coal and rock mass in the goaf increases with the advancement of the working face.In the vertical direction,due to the existence of the key layer,the subsidence displacement decreases with the increase of height,and the maximum subsidence displacement is 3.5m;The stress in the stope is redistributed to form three areas of stress concentration,pressure relief and stress recovery.In the pressure relief area,the overlying coal rock is severely damaged and the cracks are fully developed,forming a dominant channel for gas migration;the stress concentration area is mainly located in the The goaf supports the coal pillar and the working face,and its value increases with the advancement of the working face,and decreases with the increase of height along the vertical direction.The maximum value of the stress concentration factor is 2.55.Based on the uniaxial compression test,it is found that the fracture development of coal rocks presents "H" and "Y" type differentiation.With the help of SEM,CT scanning technology and other technical means,it is found that the damaged coal body has a dual medium of pores and fractures,revealing that the coal rock under the influence of stress The characteristics of cracks in the coal and rock mass,in which a large number of isolated pore structures in the coal and rock mass become the space for storing gas,and the gas moves in the coal and rock mass in two forms of diffusion and seepage;the coal and rock mass is simulated by using the Absolute Permeability Experiment Simulation of Avizo software Affected by stress,the damage degree has an exponential relationship with the permeability of coal and rock mass.The unit permeability of coal mass with different damage degrees differs by 7.71 times,and the unit permeability of different damaged rock mass differs by445.03 times.The sensitivity of rock mass to damage is high..Introducing the concept of "equivalent fracture",deduced the elastoplastic coal-rock seepage model,and carried out the coal-rock triaxial penetration test,revealing the law of exponential growth of the damaged coal-rock seepage evolution during the mining process.Combining the stress field,seepage field,damage law,and diffusion law,a fluid-solid coupling mathematical model of coal-rock mass elasticity and plastic failure was established.With the help of COMSOL multi-physics numerical simulation software,the coal seam drainage boreholes and large-diameter tail pumping boreholes were analyzed.Numerical simulations have been carried out on the drainage methods under various boundary conditions such as high-level fracture holes and high-level fracture holes.In this way,the universality of the derivation model was verified;through the analysis and comparison of parameters such as coal seam permeability,adsorption deformation,extraction negative pressure,and extraction radius of the elastic model,the influencing factors of coal seam drainage were revealed,among which the coal seam permeability had great influence on The gas drainage effect is highly sensitive;based on the plastic fluid-solid coupling model,the development law of the plastic failure area around the large-diameter tailing drilling hole increases with the increase of stress,and the plastic failure of the working face leads to failure of the drainage drilling and The law of the increase of gas emission and preliminarily determined the optimal parameter configuration of the high-level drilling,that is,the reasonable interval of the high-level drilling on the roof with a diameter of 150 mm is not less than 3.5m.Combined with the subsidence of the overlying coal and rock in the goaf,the development and evolution of fractures,and the movement of gas in the stope,a multi-physics field condition control equation for gas migration in the stope was established,and different drainage mechanisms and drainage parameters were simulated based on Fluent fluid numerical analysis.The law of gas migration in the goaf under the same conditions reveals that the large-diameter tail pumping borehole can well change the direction of the wind flow in the goaf and intercept the gushing of goaf gas,and the best drainage position is determined to be 5 behind the working face.The position of-15m;analyzed that the best extraction position of the high-level drilling on the roof is 30 m away from the return airway,and the height is at a position of 35-50 m from the roof,and carried out engineering practice on the 2-105 working face of Tenghui Mine for similar mines It provides a reference for the prevention and control of gas disasters and the realization of coal and gas co-mining.This dissertation has 113 pictures,20 tables,and 200 references...