Experimental Study of the Seepage Characteristics of Loaded Coal Under True Triaxial Conditions

Gas-bearing, coal-bearing rocks are affected by geological structures and mechanical disturbances. A stress environment exists in an unequal three-way pressure state. To determine the mechanisms of stress change that influence the fissure evolution in stratified coal under true triaxial conditions, different stratifications (vertical, horizontal and oblique stratifications) are experimentally studied based on coal gas permeability. The coal samples are investigated using scanning electron microscopy and transmission electron microscopy to analyze the microstructure differences of the coal samples before and after loading. The results show that the permeability of the different stratified coal samples is exponentially related to the maximum principal stress, the intermediate principal stress, the minimum principal stress and the effective stress. The initial permeability of the vertically stratified coal samples is only 13.5%, which is 22.2% of that for skewed bedding. The bedding direction has a significant effect on the seepage characteristics of the coal samples. In the past, most scholars ignored the influence of bedding when conducting permeability tests. The results of this paper have important theoretical and practical value for optimizing the parameters of gas drainage, increasing the gas drainage rate and reducing the greenhouse effect caused by gas emissions.