Experimental Study On Mechanical Characteristics And Seepage Characteristics Of Coal Containing Methane Under The Coupling Effect Between Stress And Thermal

Coal and gas outburst is an extremely complex geo-dynamic phenomenon in coal mining, it makes a large amount of coal dust outburst into roadway and stope and emits a lot of gas,it always causes many people dead and leads to money loss. However, the true 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 on mechanical characteristics and seepage characteristics is important to prevent coal and gas outburst disasters.Taking coal from Zhaozhuang and Sihe coal mine of Jincheng Anthracite Mining Group in Shanxi province as the research object, using the self-developed triaxial servo-controlled seepage equipment for hot-fluid-solid coupling of coal containing methane, permeability experiments and triaxial compression experiments under different temperatures, different stress, different gas pressure are carried out, then the effect of temperature, stress and gas pressure on mechanical characteristics and permeability characteristics of coal containing gas is studied. Based on the experiments above, the main research results are as follows:1) An experimental study of the impact of temperature, stress and gas pressure on mechanical characteristics of coal containing gas is carried out, and the results show that: when confining stress and gas pressure keep constant, as temperature increases, axial strain and radial stain of coal containing gas increase, volumetric strain decreases, values of failure angles increase, triaxial compressive strength, elastic modulus and poisson's ratio all decrease; when temperature and gas pressure keep constant, as confining stress increases, stain of coal containing gas decreases, triaxial compressive strength and elastic modulus increase, but poisson's ratio decrease; when temperature and confining stress keep constant, as gas pressure increases, axial strain and radial stain of coal containing gas increase, volumetric strain decreases, the characteristics of elastic deformation are more obvious, values of failure angles increase, triaxial compressive strength and elastic modulus decrease, poisson's ratio increases.2) An experimental study of the impact of temperature, stress and gas pressure on seepage characteristics of coal containing gas is carried out, and the results show that: when axial stress, confining stress and gas pressure keep constant, as temperature increases, permeability of coal containing gas decreases; when temperature and gas pressure keep constant, as effective stress increases, permeability of coal containing gas decreases; when temperature and effective stress keep constant, as gas pressure increases, permeability of coal containing gas increases. Based on the analysis of the experiment results, the influence mechanism of temperature, effective stress and gas pressure is promoted preliminarily: the increase of temperature lead to the expansion of coal particles, and then the volume of pores and cracks in a coal sample decreases, the seepage channel decreases and it causes permeability decrease; the increase of effective stress makes pores and cracks be compressed and it causes permeability decrease; gas pressure increases, the driving force for the flow of gas is enhanced, which cause permeability increase.3) During the study of the impact of temperature on the permeality of coal containing gas, a temperature sensitivity coefficient is defined to eliminate the deviation due to individual difference, and based on that the influence of temperature on permeability is studied objectively.4) In the study of the evolution of seepage velocity as the strain of coal containing gas in triaxial compression process, it is found that the change of seepage velocity lags behind the change of the strain of coal samples. Then the paper carries out a quantitative study of the lag effect of seepage velocity. At first,"the lagged quantity when the coal sample reaches its minimum volume"and"the lagged quantity when the macroscopic failure begins in the coal sample"are defined to reflect the lag effect quantitatively. After that the values of the two lagged quantities under different experimental conditions are determined based on the experiment results, and the paper also analyses the generation mechanism preliminarily.5) Comparisona are made between moulded coal and raw coal, the results show that: when experimental conditions are the same, the triaxial compressive strength and the elastic modulus of moulded coal samples are less than those of raw coal samples, but the strain and the possion's ratios are more than those of raw coal samples; permeability of moulded coal is much more than that of raw coal; the sensitivity of moulded coal to temperature is less than that of raw coal; lag effect of moulded coal samples is more obvious than that of raw coal.