Research on pre- drainage gas equivalent width of roadway under seepage-stress coupling

It is of great significance to accurately determine the pre-drainage gas width of roadway for prediction of mine gas emission,evaluation of drainage stand ards and improvement of prevention and control effect of gas disaster in roadway.In order to determine reasonable pre-drainage gas width of roadway,the elastoplastic mechanical model of the coal body around the roadway considering the strain softening and dilatancy characteristics was deduced,and the analytical expressions of the stress and volume strain of the coal around the roadway were obtained,and the gas migration coupling model considering the roadway pressure relief and matrix shrink age effect was established based on the permeability as a bridge.The gas migration law and influencing factors of coal around the roadway was found out,and pre-disch arge gas equivalent widths with different conditions were determined.The results show that: the gas migration around the roadway is controlled by the stress field and th e seepage field,and the larger the roadway pressure relief range is,the more the coal body's permeability increases,which is more favorable for gas discharge.Discharg e time,permeability coefficient of coal seam,ground stress,coal body strength,supporting stress,roadway size and metamorphic grade are the main factors to control pre -discharge gas equivalent width. The pre-discharge gas equivalent width with discharge time of 60,120, 180,and 240 d are 9.2,11.9,13.8,and 15.3 m,which increase with the increase of discharge time.The pre-drainage gas width of coal layer for 180 d that is difficult to gas drainage is less than 15 m,and the coal layer that can be drainag edis 15 ~ 20 m,and the easy drainage of the coal layer is more than 20 m,and the pre-drainage gas width of roadway gradually increases with the increase of the coal permeability coefficient. Ground stress,coal body strength, supporting stress and roadway size affect gas migration by controlling coal body deformation. The pre-drainag e gas width of roadway is directly proportional to discharge time,coal seam permeability coefficient and roadway size,and coal body strength,ground stress ,supporting st ress and metamorphic degree are inversely proportional.Pre-discharge gas equivalent width of test roadway with discharge time 120 d is determined 11.9 m,and the gas content test result shows that it is reasonable and reliable.