The Influence of Cyclic Loading Amplitude on Delayed Rockburst: Insights from True Triaxial Disturbance Experiments
摘要
Dynamic disturbance loads generated during underground excavation are a critical factor in triggering delayed rockburst, and their magnitude governs the scale and severity of these events. To investigate the influence of disturbance load amplitude on delayed rockburst, we simplified the disturbance as cyclic loading and conducted true triaxial experiments on specimens with prefabricated circular holes subjected to varying cyclic loading amplitudes (4, 8, 12, and 16 MPa). The experimental process was monitored and recorded in real-time using image and acoustic emission (AE) monitoring systems. The results revealed that with increasing cyclic loading amplitude, the failure modes transition from slabbing to spalling and eventually to rockburst. Spalling produces slab-like fragments, while rockburst generate a diverse range of fragments, including both slab-like and blocky forms. As the cyclic loading amplitude increases, the failure mode transitions through these stages, accompanied by intensified rockburst activity, reduced time to rockburst initiation, higher fragment fractal dimensions, increased cumulative AE energy, a greater proportion of low-frequency, high-amplitude signals, elevated AE shear signal ratios, and higher maximum AE entropy. Compared to spalling under low-amplitude disturbance, rockburst under high-amplitude disturbance exhibit a distinct quiet period in AE activity, followed by a linear increase in AE entropy, an indicator that can be a precursor for rockburst prediction.
Highlights Delayed rockburst under cyclic loading was investigated via true triaxial tests. The relationships among slabbing, spalling, rockburst, and cyclic load amplitude were clarified. The linear growth phase of AE entropy provides a potential early warning indicator. The damage coefficient's relationship with the number of cyclic loads helps predict delayed rockburst occurrence time.