Temporal-spatial evolution characteristics of defective coal fracture based on electric potential and multifractal characterization

The primary defects in coal are critical factors that induce geological disasters. Accurately predicting and identifying local damage in these defects is essential for the safe mining of underground engineering. In this paper, uniaxial compression tests were conducted on defective coal, and acoustic emission (AE) and electric potential (EP) were tested simultaneously. The mechanical behavior and failure characteristics were studied, the EP and AE features were analyzed, and the temporal-spatial features of the EP multifractal were revealed. The results indicate that external loads significantly stimulate both AE and EP responses in the coal sample, which correlate well with stress changes. As the defect dip angle increases, high-amplitude AE signals gradually decrease, and the main frequency distribution of AEs shifts from a full frequency range to a mid-low frequency range. The EP signals of each channel correspond closely with its corresponding strain evolutions, and the EP signals near the local damage area exhibit regions of high-value abnormal Δα_e and low-value abnormal Δf(α_e). When macroscopic fracturing occurs, Δα_e shows a fluctuating increase, while Δf(α_e) shows a fluctuating decrease. The spatiotemporal distribution of Δα_e and Δf(α_e) corresponds well with the stress levels and local damage in the sample. These research results provide significant theoretical guidance for the early warning and precise identification of geological disasters.