Strainburst process of marble in tunnel-excavation-induced stress path considering intermediate principal stress

Strainburst is one type of rockburst that generally occurs in deep tunnel. In this study, the strainburst behaviors of marble specimens were investigated under tunnel-excavation-induced stress condition, and two stress paths were designed, a commonly used stress path in true triaxial unloading rockburst tests and a new test path in which the intermediate principal stress was varied. During the tests, a high-speed camera was used to record the strainburst process, and an acoustic emission (AE) monitoring system was used to monitor the AE characteristics of failure. In these two stress paths, all the marble specimens exhibited strainbursts; however, when the intermediate principal stress was varied, the rockburst became more violent. The obtained results indicate that the intermediate principal stress has a significant effect on rockburst behavior of marble. Under a higher intermediate principal stress before the unloading, more elastic strain energy was accumulated in the specimen, and the cumulative AE energy was higher in the rockburst-induced failure, i.e., more elastic strain energy was released during the failure. Therefore, more violent failure was observed: more rock fragments with a higher mass and larger size were ejected outward.