Acoustic emission characteristics and failure precursors under uniaxial cyclic compression

Understanding the damage evolution and failure mechanisms of brittle rocks is crucial for evaluating the long-term stability of underground engineering structures. In this study, uniaxial cyclic compression tests were conducted on marble specimens, and acoustic emission (AE) monitoring was employed to investigate microcrack initiation, propagation, and coalescence. A comprehensive analysis integrating AE event characteristics, three-dimensional localization, b-value evolution, and fractal dimension computation was performed. The results demonstrate that marble failure can be divided into three stages: a rising stage dominated by pore compaction and microcrack initiation, a quiet stage reflecting the Kaiser effect, and a violent stage characterized by rapid crack coalescence and energy release. Spatial localization reveals that AE events transition from scattered distributions at low stress to concentrated clusters along the eventual fracture surface. The dynamic variation of the b-value indicates damage accumulation, with a sustained decrease serving as a critical precursor to failure. Meanwhile, the fractal dimension exhibits a characteristic “decrease–increase–decrease–increase–sharp drop” pattern, capturing the evolving complexity of crack systems. These findings highlight the combined utility of b-value and fractal dimension analyses for identifying precursors of instability and provide a scientific basis for AE-based stability monitoring and early warning in rock engineering.