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

Abstract

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.

摘要

应变型岩爆常发生于深埋隧道中, 是岩爆的基本类型之一。本文利用自主研制的真三轴试验系 统对大理岩试样开展隧道开挖应力路径下应变型岩爆过程试验研究。设计了两种试验路径, 一种是常 用的真三轴卸载岩爆试验路径, 另一种是考虑隧道开挖过程中围岩中间主应力变化的新试验路径。试 验过程中, 应用高速摄像机记录岩样卸载临空面应变型岩爆破坏过程, 并应用声发射监测系统监测岩 样破坏过程中的声发射特征。试验结果表明: 两种试验路径下岩样均发生了应变型岩爆破坏现象, 但 新试验路径下岩样应变型岩爆过程更剧烈, 表明中间主应力对大理岩的岩爆行为具有显著的影响; 卸 载前中间主应力越大, 岩样内积聚的弹性应变能越多, 破坏过程中累计声发射能量越大, 即岩样破坏 时释放的弹性应变能越多, 岩样发生岩爆破坏时弹射碎屑的总质量越大、粒度越大, 破坏过程越剧烈。