Effects of cyclic stress lower limit on the mechanical behavior and energy instability precursor characteristics of rock with hole-shaped flaw

Abstract

Cyclic compression tests are conducted to investigate the effects of cyclic stress lower limits on the mechanical behavior and energy response of rocks with hole-shaped flaw. The results show that increasing the stress lower limit accelerates internal damage accumulation and promotes an apparent hardening. This is manifested in a higher loading and unloading moduli, reduced peak strength and plastic deformation, and a transition toward more brittle and catastrophic failure behavior. When the stress lower limit approaches zero, the rock exhibits softening behavior and undergoes a relatively mild failure process, with failure primarily localized along a single dominant shear band through the flaw. From the perspective of energy, the gradual increase of stress lower limit has produced more instability characteristics. The energy storage (or release) rate initial increases and then decreases, exhibiting a peak prior to failure. While the energy dissipation rate rises monotonically. In contrast, under a constant stress lower limit, the energy rate evolves steadily without significant mutation. Finally, an energy-based instability precursor indicator is established based on the energy rate difference (ERD) and its effectiveness is also evaluated through correlation with acoustic emission (AE) characteristics during cyclic loading. ERD exhibits a more pronounced and sensitive instability precursor signature compared to conventional indicators, where both the peak value and the rate of post-peak decline provide quantitative insight into the severity of impending failure. This makes ERD a robust and reliable tool for predicting the instability of flawed rock masses under cyclic loading.