Investigating nonlinear resistivity characteristics and mechanisms of coal during various loading stages

Abstract

Accurately revealing the resistivity response patterns during coal fracture caused by loading and failure process of coal is fundamental to the application of DC resistivity methods in detecting coal dynamic disasters. This work delves into the intricate variability patterns of electrical resistivity exhibited by coal across diverse loading phases, and finds that there is fluctuation in electrical resistivity during the coal failure process, rather than the linear function relationship obtained in previous studies. The fluctuation in resistivity during the coal fracture process arises from the closure of existing fractures and the generation of new fractures. The former decreases resistivity, while the latter increases it, and their combined effect causes resistivity to fluctuate. Through long-range correlation analysis, it was found that the electrical resistivity of coal exhibits significant self similarity during the loading and fracturing process, with a Hurst exponent H higher than 0.98. The resistivity during coal fracture process exhibits fractal characteristics, with fractal box dimensions of 1.328 and 1.450 for the resistivity of the two samples, respectively. The fluctuation of resistivity during the loading process of coal is closely related to the compression process and development of fractures. In the four stages of coal sample loading, fractures evolve from initial formation, expansion to complete fracturing, with the fractal box-counting dimension exhibiting a trend of increase-increase-decrease. These research findings provide new insights into using resistivity inversion for coal fracture detection, which is of significant importance for the development of resistivity technology.