Experimental Study Seepage Characteristics Of Coal Containing Methane Under Cyclic Loads Pressure

Coal and gas outburst is an extremely complex geo-dynamic phenomenon in coalmining, it makes a large amount of coal dust outburst into roadway and stope and emitsa lot of gas,it always causes many people dead and leads to money loss. However, thetrue mechanism of coal on coal and gas outburst is not exactly proved. Therefore,making a comprehensive study of the impact of temperature, stress and gas pressure onmechanical characteristics and seepage characteristics is important to prevent coal andgas outburst disasters.Taking coal briquette coal samples as the research object, using the self-developedtriaxial servo-controlled seepage equipment for hot-fluid-solid coupling of coalcontaining methane, triaxial compression experiments under different temperatures,different coal particle size and cyclic loading experiments are under differenttemperatures, different coal particle size different settling time carried out, then theeffect of temperature, coal particle size and settling time on mechanical characteristicsand permeability characteristics of coal containing gas is studied. Based on theexperiments above, the main research results are as follows:1) An experimental study of the impact of temperature and coal particle size onmechanical characteristics of coal containing gas is carried out, and the results showthat: when confining stress and gas pressure keep constant, as temperature increases,axial strain of coal containing gas increase, volumetric strain and radial stain decreases,,triaxial compressive strength and elastic modulus all decrease; when temperature andgas pressure keep constant, as coal particle size decreases, stain of coal containing gasdecreases, elastic modulus increase, coal particle size of60to80mesh standardbriquette triaxial compressive strength are highest;2) An experimental study of the impact of temperature and coal particle size onseepage characteristics of coal containing gas is carried out, and the results show that:when axial stress, confining stress and coal particle size keep constant, as temperatureincreases, permeability of coal containing gas decreases, the increase of temperaturelead to the expansion of coal particles, and then the volume of pores and cracks in a coalsample decreases, the seepage channel decreases and it causes permeability decrease;the increase of effective stress makes pores and cracks be compressed and it causespermeability decrease; gas pressure increases, the driving force for the flow of gas is enhanced, which cause permeability increase; when temperature,gas pressure keepconstant, as coal particle size decreases, permeability of coal containing gas decreases;3) An experimental study of the impact of temperature, coal particle size andsettling time on deformation characteristics of coal containing gas under cyclicloading is carried out, and the results show that: when confining coal particle size andsettling time keep constant, as temperature increases, volumetric strain increase; whentemperature and settling time keep constant, as coal particle size decreases, stain of coalparticle size of60to80mesh standard briquette are highest; when confining coalparticle size and temperature keep constant, as settling time increases, volumetric straindecrease, the degree of deformation of the coal samples; under various experimentalconditions, the deformation of coal are closely related to the number of cyclic loadingand unloading, with the increase of the cycle, the strain tends to stabilize deformationstage;4) An experimental study of the impact of temperature,coal particle size andsettling time on seepage characteristics of coal containing gas under cyclic loading iscarried out, and the results show that: when coal particle size and settling time keepconstant, the highest temperature of coal, the coal sample loop and upper seepagevelocity loop lower limit stress highest; when temperature and settling time keepconstant, as coal particle size decreases, permeability of coal containing gas decreases;when confining coal particle size and temperature keep constant, as settling timeincreases, the smaller the decline of the coal sample gas seepage velocity; coal samplevolume deformation and seepage velocity has the same trend with the change of thenumber of cycles, the gas in coal samples seepage characteristics and its deformation isclosely related.