Investigation of the evolution of damage and permeability of coal containing gas based on acoustic emission characteristics

The gas permeability of a coal seam was the main factor determining the efficiency of gas extraction from the mines and was closely related to the coal damages. In this paper, a triaxial compression failure test of the raw coal was carried out in the gas seepage state using the MTS 815 rock mechanics testing system. The damage evolution law of the coal containing gas under triaxial compression was studied based on acoustic emission characteristics. The damage evolution parameters were determined using acoustic emission signals, and the relationship between the permeability and damage evolution of the coal containing gas was quantitatively analyzed. The results demonstrated that the acoustic emission signals could reflect the development of the damage and failure inside the coal, and the turning point of the acoustic emission characteristic curve marked different damage development stages. The periodic changes in the permeability of the coal samples were consistent with the damage change law, and some lag existed in permeability changes compared with damage evolution. The permeability of the coal containing gas saw a stepwise exponential growth with the damage development. The piecewise exponential function better reflected the relationship between the gas permeability and damage variables.