| Due to the exploitation of coal resources for many years,coupled with the scarcity of shallow coal resources in China,the mining depth of China's mines has been increasing.After deep mining,the geological conditions of coal seam become complicated,and the outburst risk of coal and gas becomes bigger.Protective bed mining is the most economical and effective regional gas control technology to prevent and control coal and gas outburst.However,facing the situation that there is no suitable protective bed to choose from in deep area,the traditional protective bed mining method encounters the bottleneck.Based on leveling.Mine has 15 to 17 coal seam without appropriate protective layer mining as the research background,the traditional system test has 15 to 17 coal seam coal physical parameters,put forward the exploitation of a new type of protective layer mining on soft rock layer,using the method of numerical simulation combined with field investigation of protective layer on the soft rock mining unloading effect were studied.The specific research contents of this paper are as follows:(1)Through laboratory experiments,the basic physical parameters,pore structure and adsorption and desorption properties of coal samples are systematically studied.It is concluded that Ji 15-17coal is a soft coking coal with medium metamorphism degree,and the micropores and pores in the coal samples are well developed.From the adsorption and desorption experiments,the maximum value of gas adsorption constant A of the coal sample is 28.4008 m3/t.The gas adsorption capacity is strong and the gas is released quickly,which is equipped with the conditions for large-scale outburst.(2)Through a number of parameters and geological conditions of coal seam,the outburst risk is evaluated from the perspectives of gas occurrence,gas outburst zoning and coal thickness change,the selection of gas outburst prevention methods is demonstrated from the aspects of technical factors and economic benefits,and the feasibility of soft rock protective layer is discussed.(3)Using FLAC3Dnumerical simulation method,the displacement and stress changes of the underlying coal and rock mass and the failure of the plastic zone in the process of mining the protective layer on soft rock are analyzed theoretically,and the law of pressure relief effect of mining the protective layer on soft rock is obtained.Under the different face advance distance and the vertical displacement variation that increases with the increase of advance distance,stress increases quickly,before they are emerging slowly reduce the change of the state,the plastic zone along with the increase of advance distance and increasing,plastic damage did not happen,but some of the hard rock and destroyed by protective plastic significantly.The comprehensive gas control measures to ensure the safety of coal seam mining in Ji 15-17coal seam with soft rock as the core are comprehensively expounded.The field test was carried out in the 15-17 coal seam of Pingdingshan 13 mine,and the gas extraction effect,pressure relief boundary and expansion deformation rate were investigated in the field.according to the results of soft rock mining protective layer,after pressure relief range puckering average gas concentration less unloading area increased by 160%,at least after unloading extraction from scalar's 32 times,before the pressure relief to the pressure relief boundary for starting cut in soft rock cover level within 9.5 m wrong place,tendency for soft rock layer on the wind pressure relief boundary,machine lane level to face the wrong wrong within 4.3 m,The maximum expansion deformation rate of the protected layer is 8.92‰.There are 72 figures,29 tables and 79 references in this paper. |
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