Deformation characteristics and permeability variations induced in the coal matrix induced by thermo-mechanical coupling

To evaluate the coal deformation characteristics and explore the evolution law of coal permeability under different conditions, the MTS815 and PCI-2 acoustic emission (AE) test systems were applied to conduct the triaxial percolation test under other thermo-mechanical coupling conditions, and the fractal model of coal fractal with integrated stress and temperature was established. The results indicated that the peak stress, strength and deformation parameters of the samples were positively correlated with the confining pressure. The temperature can promote the crack propagation, derivation and new cracks of coal samples. The macrocracks and percolation channels space inside the samples increased with the increase of the thermal-mechanical coupling condition. The AE signal was mainly released in the plastic and peak phases; the growth of confining pressure intensified the aggravation of the internal damage to the coal sample and caused the frequent occurrence of AE signals. The compressive coefficient Cf of coal fracture decreased with the addition of average effective stress, and the ruptured coal had the same trend with the increase in pore pressure; the calculated values of the new thermally sensitive model were consistent with the measured values. The applicability of the theoretical mechanism and the data matching were of high credibility.