This study systematically investigated the damage evolution in cemented tailings backfill with varying initial defect levels (C1, C2, C3) using uniaxial compression tests and simultaneous acoustic emission (AE) monitoring. The temporal patterns of key AE parameters—ringing counts, amplitude, peak frequency, and energy—were analyzed. By integrating \(I_{b}\) value and RA-AF analysis, the influence of initial defects on damage mechanisms and failure modes was elucidated. Results show that initial defects significantly affect AE activity. Specimens with larger defects (C3) exhibited substantially higher cumulative ringing counts (> 15000 vs. ~ 6000 for C2) and intense energy release during early loading, characterized by elevated maximum amplitudes (up to 72 dB vs. 57 dB in C2), broad frequency distributions (spanning 0–27 kHz), and pronounced \(I_{b}\) value fluctuations (ranging from 1.76 to 2.18). In contrast, specimens with smaller defects showed weaker AE activity and a relatively smoother failure progression. After peak stress (0.797 ~ 0.806 MPa), frequency responses declined across all specimens, corresponding to stages of crack propagation and penetration. RA-AF analysis indicated that tensile failure was dominant initially, but as loading progressed into the elastic–plastic stage, the proportion of shear cracks increased progressively. Notably, larger initial defects delayed the onset of dominant shear failure. By quantifying the coupled evolution of AE parameters and failure modes specific to defect-laden cemented backfill, this study provides a novel quantitative theoretical basis for damage assessment and stability prediction in cemented tailings backfill engineering.
