Nonlinear evolution characteristics of acoustic emission and fracture mechanism of coal under gas pressure

The study on the evolution characteristics of acoustic emission of coal containing gas plays an important role in revealing the deformation and failure mechanism of coal.The triaxial compression tests on the coal containing gas is carried out by using the seepage stress coupling test system.The influence of gas pressure on the nonlinear evolution characteristics of acoustic emission of coal are studied, and the influence mechanism of gas pressure on coal strength is analyzed based on the strength theory.The results show that there is a good corresponding relationship between the acoustic emission energy and the volume strain evolution of coal.With the decrease of gas pressure, the acoustic emission energy increases rapidly, and the stage curve becomes more steep, which also indicates that the brittle failure characteristics of coal are strengthened.The fractal number of acoustic emission decreases before the peak and increases after the peak.At the pre-peak stage, the decrease of fractal dimension indicates the increase of micro-fracture and the appearance of main fracture in coal, and the internal damage of coal gradually transits from disordered random distribution to macro-ordered failure.