Non-destructive evaluation of failure mechanisms in multilayered coal-rock specimens using acoustic emission characterisation

This study presents a multi-parameter Acoustic Emission (AE) framework to evaluate failure mechanisms in coal-rock composites. Using uniaxial compression tests with varying coal-seam dip angles (0°–60°) and thickness ratios (1:3 to 3:1), we developed an AE-based methodology that integrates three key analyses: (a) stress–strain relationships, (b) cumulative AE energy/count evolution, and (c) b-value transitions. Results show that structural anisotropy significantly influences failure modes. Increased dip angles (45°/60°) enhanced strength by 18.7–23.4% due to better stress redistribution, while higher coal-layer ratios decreased load-bearing capacity by 27.3% due to interfacial decohesion. The b-value transition sequence (fluctuation → stabilisation → critical minimum → recovery → sudden decay) provides reliable precursors for predicting failure, correlating 82–94% with macroscopic fracture initiation. This research advances AE-based non-destructive testing by quantifying interfacial damage through energy dissipation patterns and predicting instability using b-value trajectories. The proposed method enables real-time monitoring of structural integrity in complex geological environments, with applications in mining support and early-warning systems.