Effects of damage on resistivity response and volatility of water-bearing coal

A series of experimental geophysical methods with resistivity as the key parameter provide strong support for predicting and providing early warnings of geological disasters. In this study, coal samples with similar P-wave velocities and pore distributions were screened, and a weighing method was used to control the water content of the coal samples. A real-time test system was independently constructed to conduct uniaxial compression tests on these coal samples and synchronously monitor resistivity and acoustic emission (AE) data. The results show that resistivity obviously characterizes the process of coal failure under load. The development of microfractures causes fluctuations. The resistivity changes relatively smoothly before the development of fractures, and resistivity fluctuations are obvious during the development of fractures. The resistivity fluctuation range reaches the maximum when the whole fracture occurs at the stress peak, but the presence of water weakens the resistivity fluctuations during the whole process of failure. Water migration causes circuit reconnection and changes the fluctuations. With increasing water content, the uniaxial compressive strength (UCS), elastic modulus (E) and maximum AE amplitude decrease. The resistivity variation at the peak value also decreases. Under the condition of 9.2% water content, the resistivity variation at the peak stress is only 2.52%. The results prove that violent fluctuations of resistivity correspond to the development of microfractures in the sample, and the amplitude of the fluctuations is positively correlated with the degree of damage and fracture. The volatility index (Resistivity Standard Deviation, RSD) is established to describe the degree of resistivity fluctuation, and the peak value occurs when the AE energy increases sharply. The establishment of a volatility index aims to provide a new parameter for rock damage and dynamic disaster prediction technology.