Abstract: To investigate the effect of various intermediate principal stresses on rockburst incubation and failure during tangential stress gradient loading, a series of true triaxial rockburst model experiments on quasi-rock material specimens under three intermediate principal stress conditions was conducted using a self-developed gas-liquid combined loading apparatus. A high-speed camera and an acoustic emission monitoring system recorded the test data. This paper compared and analyzed the macroscopic failure differences of the specimens and the evolution characteristics of acoustic emission parameters. The results indicate that the failure load, instantaneous burst intensity of rockburst, total mass of rockburst debris, mass of debris of each particle size, and scale of specimen failure increase with higher intermediate principal stress. During loading, specimens under high intermediate principal stress show weakened acoustic emission activity in the early and middle stages, revealing that the high intermediate principal stress suppresses the damage and crack development. In the later stages, the acoustic emission ringing count and energy release of the specimens under high intermediate principal stress become more concentrated, and the energy peak and cumulative values increase. The acoustic emission b-value drops sharply to a lower level, and the proportion of high main frequency amplitude points increases, indicating that high intermediate principal stress exacerbates the damage and crack development. The number of large-scale and shear cracks increases, leading to more violent instantaneous energy release, more severe failure, and higher intensity of rockburst.

Key words: rockburst, gradient stress, intermediate principal stress, macroscopic failure, acoustic emission