Influence of disturbance frequency on rockburst in circular openings: insights from cyclic loading experiments

Rockbursts induced by cyclic loading are a major hazard in deep underground excavations. Among the influencing factors, the cyclic loading frequency ( f c ), typically generated by blasting or mechanical excavation, plays a critical role in controlling the initiation and progression of rockbursts. In this study, true triaxial rockburst experiments were conducted on sandstone specimens containing a circular opening to investigate the frequency-dependent failure characteristics. Four values of f c (0.25, 0.5, 0.75, and 1 Hz) were applied, and the failure processes were monitored using real-time video recording and acoustic emission (AE) techniques. The evolution of energy release, velocity fields, and AE spatial distribution was quantitatively analyzed. Post-failure fragments were further examined using scanning electron microscopy (SEM) to assess internal damage. The results indicate that although the total input energy remained nearly constant, higher f c significantly increased the energy release rate and fragment ejection velocity. SEM observations reveal that increasing f c leads to a higher pore density and more pronounced pore connectivity. Image-based porosity analysis shows a clear increasing trend, reflecting progressive internal degradation. The development and accumulation of these pores accelerate strength deterioration, which promotes the earlier intersection of the Mohr stress circle with the weakened Mohr–Coulomb failure envelope, thereby advancing failure onset . The results demonstrate the critical role of disturbance frequency in rockburst triggering, enabling more effective control of excavation disturbances in underground construction.