Dynamic response mechanism and precursor characteristics of gneiss rockburst under different initial burial depths

To investigate the influence mechanism of geostress on rockburst characteristics, three groups of gneiss rockburst experiments were conducted under different initial geostress conditions. A high-speed photography system and acoustic emission (AE) monitoring system were used to monitor the entire rockburst process in real time. The experimental results show that when the initial burial depth increases from 928 m to 1320 m, the proportion of large fracture scale in rockburst increases by 154.54%, and the AE energy increases by 565.63%, reflecting that the degree and severity of rockburst increase with the increase of burial depth. And then, two mechanisms are proposed to explain this effect, including (i) the increase of initial geostress improves the energy storage capacity of gneiss, and then, the excess energy which can be converted into kinetic energy of debris ejection increases, consequently, a more pronounced violent ejection phenomenon is observed at rockburst; (ii) the increase of initial geostress causes more sufficient plate cracks of gneiss after unloading of σ_h, which provides a basis for more severe ejection of rockburst. What's more, a precursor with clear physical meaning for rockburst is proposed under the framework of dynamic response process of crack evolution. Finally, potential value in long term rockburst warning of the precursor obtained in this study is shown via the comparison of conventional precursor.