Acoustic emission – based damage staging and transition indicators of instability in coal-measure roof rock composites under uniaxial compression

Layered coal-measure roofs contain lithological heterogeneity and bonded interfaces, which complicate quantitative non-destructive evaluation (QNDE) of instability. This study examines four field-derived roof-rock composite configurations (LS–C, LS–AS, LS–C–MS and LS–MS–AS) under uniaxial compression using acoustic emission (AE) monitoring, RA–AF crack-mode classification and source localisation. Three valid tests were retained for each single-lithology and composite configuration. The mean UCS values of LS–C, LS–C–MS, LS–MS–AS and LS–AS were 15.58 ± 0.98, 11.97 ± 0.32, 58.83 ± 0.72 and 86.43 ± 1.95 MPa, respectively, indicating strong configuration dependence. A normalised AE-state change rate, derived from b-value, S-value and cumulative-count histories, was used with the transition stress ratio λt = σt/σp to identify dominant AE-state changes before peak strength. In the measured records, λt ranged from 0.098 to 0.955 and was sensitive to event-window length. Configuration-specific RA–AF boundaries showed tensile-dominated failure in all composites (>83%), while AE localisation separated interface-controlled clustering from multilayer damage zones. Instability was therefore controlled jointly by lithology, thickness ratio, layer sequence and bonded-interface behaviour, rather than layer number alone.