A carbon fiber-based self-sensing approach for monitoring damage evolution in coal pillars

Under long-term high stress and dynamic disturbances, damage accumulation within underground coal masses can induce sudden instability, posing a considerable threat to coal mine safety. Real-time acquisition of coal damage information is essential for disaster prevention and control. This study proposes a coal damage and fracturing monitoring approach based on a carbon fiber composite mortar (CFCM) coating. By applying the CFCM coating to coal specimen surfaces and monitoring resistance changes, the dynamic evolution of damage can be tracked. The study combines experimental mechanical loading, continuous electrical resistance monitoring and acoustic emission recording with detailed numerical modelling to comprehensively evaluate sensing performance and the linkage between electrical signals and fracture processes in coal specimens. The carbon fiber content strongly affects the electrical conductivity and damage-sensing capability of the CFCM coating. When fiber content exceeds 1.0 wt%, a stable conductive network forms, markedly reducing specimen resistance and suppressing signal noise. At 2.0 wt% carbon fiber, the CFCM-coated specimen achieves optimal conductivity and self-sensing capacity, with resistance noise four orders of magnitude lower than that of the uncoated specimen. Under this condition, a resistance surge (Δ RCR ) at the onset of failure corresponds closely to acoustic emission (AE) events and can serve as a precursor of coal instability. Further analysis shows the CFCM coating creates a preferential conductive pathway enveloping the specimen, directing current primarily along the coating before distributing transversely through the coal. This enhances detectability of fracturing by modifying current-field distribution and amplifying resistance variations caused by microcrack propagation. After denoising via three-level wavelet decomposition, macroscopic fracturing events can be accurately identified. The method shows promise for scalable field deployment and practical integration with existing mine safety monitoring systems. The CFCM-based monitoring approach offers a new pathway for real-time stability monitoring and early warning in underground coal masses.