Experimental study on resistivity evolution law and precursory signals in the damage process of gas-bearing coal

The occurrence of elevated gas pressure leads to the distortion of the internal pore structure within the coal matrix, thereby exerting a substantial influence on the destabilization of the coal body. This disturbance further contributes to intricate changes in coal resistivity. To delve into the process of gas-induced damage and its implications for coal resistivity, this research employs nuclear magnetic resonance (NMR) technology as a means to characterize coal samples. Moreover, a controlled loading experimental equipment is devised for gas-bearing coal, while concurrently gathering data on resistivity and acoustic emission (AE). The result shows that with increasing applied stress, the change in resistivity within gas-bearing coal exhibits a progressive intensification, manifesting a notable "V"-shaped pattern. This pattern is characterized by an initial rapid decline, succeeded by a subsequent swift increase during the failure stage. The AE signals exhibit a synchronized consistency with the observed resistivity change. With increasing gas pressure, the coal's resistivity exhibits heightened fluctuations, and notably, the range of resistivity at failure under a pressure of 3 MPa is 2.27 times greater compared to that at 0 MPa. Furthermore, the damage variable and constitutive equation for gas-bearing coal based on resistivity is established. The critical value for damage (DE) occurs 1.75 s before the critical value of the resistivity change rate, and 3.88 s earlier than the actual occurrence of damage in the coal body. The correlation between the verified damage and measured stress exceeds 0.8, demonstrating a strong correlation at different stages. The research results contribute to understanding the evolution mechanism of gas instability and hold considerable significance for preventing coal and gas outburst disasters.