Rockburst hazards exhibit different spatiotemporal characteristics in deep tunnel excavation. Failure characteristics and energy evolution process of delayed and instantaneous rockburst of basalt rock were investigated based on single-sided unloading experiments under true triaxial conditions. High-speed photography and acoustic emission (AE) monitoring were used, and computed tomography (CT) scanning, fractal theory, and crack classification were employed for failure analysis. A three-dimensional damage model considering variable stiffness of testing machine was established to calculate the energy evolution of rock-machine system during the entire process of rockbursts. Results show that delayed rockburst includes three stages of small particles ejection, rock slab buckling, and violent mixed ejection, while instantaneous rockburst is characterized by rock slab spalling accompanied with slight particles ejection. Delayed rockburst exhibits a progressive failure mode of large-scale expansion of tensile cracks (before failure) to small-scale penetration of shear cracks (upon failure), while instantaneous rockburst shows a large-scale shear failure and abrupt penetration of shear planes upon failure. Delayed rockburst consumes less energy, and most of dissipated energy is converted into kinetic energy of ejected rock fragments, causing a higher intensity level of rockburst; instantaneous rockburst consumes more energy, but almost all dissipated energy comes from internal friction energy of shear failure, causing a higher scale of rock damage. Before rockburst failure, elastic strain energy stored in rock remains basically unchanged, while the energy stored in testing machine continuously decreases, indicating that rockburst is triggered by energy release of loading system. Energy dissipation rate (EDR) can be used as a precursory index for rock failure induced by quasi-static loading such as delayed rockburst. High EDR means damage intensification, stress drop, active AE events, and acceleration of shear crack expansion inside the rock. The findings of this study can provide new perspectives for the mechanisms and early warning of rockbursts.

中文翻译：

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真三轴工况下延迟瞬时玄武岩地爆的破坏特征及能量演化过程


在深部隧道开挖中，岩爆灾害表现出不同的时空特征。基于真三轴条件下的单侧卸载实验，研究了玄武岩延迟和瞬时岩爆的破坏特征和能量演化过程。采用高速摄影和声发射 （AE） 监测，采用计算机断层扫描 （CT） 扫描、分形理论和裂纹分类进行失效分析。建立了考虑试验机变刚度的三维损伤模型，计算了岩爆全过程中岩机系统的能量演化。结果表明：延迟岩爆包括小颗粒抛出、岩板屈曲和剧烈混合抛射3个阶段，瞬时岩爆表现为岩板剥落伴轻微颗粒抛出。延迟岩爆表现为拉伸裂缝大面积扩展（破坏前）向小规模剪切裂缝渗透（破坏时）的进行破坏模式，而瞬时岩爆表现为大尺度剪切破坏和破坏时剪切面的突然穿透。延迟岩爆消耗的能量较少，大部分耗散的能量转化为喷出的岩石碎片的动能，导致岩爆强度更高;瞬时岩爆消耗的能量较多，但几乎所有耗散的能量都来自剪切破坏的内摩擦能，导致岩体损伤规模更大。在岩爆破坏前，岩石中储存的弹性应变能基本保持不变，而试验机中储存的能量不断减少，表明岩爆是由加载系统的能量释放触发的。 能量耗散率 （EDR） 可以作为延迟岩爆等准静态载荷引起的岩石破坏的前兆指标。高 EDR 意味着损伤加剧、应力下降、主动 AE 事件以及岩石内部剪切裂纹扩展的加速。本研究结果可为岩爆的机理和预警提供新的视角。