地下工程开挖过程中，因开挖卸荷效应和应力集中效应，使积蓄在巷道围岩内部的能量突然释放，导致巷道围岩产生岩块的动态弹射破坏现象。为揭示深埋隧道岩柱段、交叉隧道等地下工程在高应力三轴卸荷条件下岩柱岩爆的能量演化规律与破坏机理，采用自主研制的真三轴试验系统，针对四面临空岩柱受力特征，开展围压卸荷条件下的岩柱岩爆模拟试验。以尺寸200 mm×100 mm×100 mm的红砂岩为研究对象，设置10、30、50 MPa 3组围压等级，采用“三向初始应力同步加载—水平双向快速卸荷—轴向应力集中”的应力路径，还原岩柱双向开挖卸荷与应力重分布过程。通过高帧率摄像、粒子图像测速技术，获取岩爆破坏过程、碎屑弹射速度与宏观裂纹扩展特征，结合热力学第一定律与真三轴能量计算方法，系统分析总能量、弹性能与耗散能的积聚、转化与释放规律，阐明围压对岩爆能量演化的调控机制。结果表明： 1）三轴水平快速卸荷路径下，岩石试样的峰值强度存在显著的围压效应，试样峰后应力跌落速率随围压升高显著增大，岩爆脆性破坏特征显著增强； 2）卸荷阶段试样出现明显塑性变形与卸荷扩容现象，该特征为常规三轴试验难以复现的力学响应； 3）不同围压水平卸荷条件下，耗散能与弹性能存在明显的能量竞争演化机制； 4）岩石试样在峰值应力处的3种能量均随围压的增大而增大，围压对总能量的增长速率影响最大，对耗散能的增长速率影响次之，对弹性能的增长速率影响最小。
In the excavation of underground engineering, the internal energy stored in rock elements is suddenly released due to the effects of excavation unloading and stress concentration in the surrounding rock, resulting in the dynamic ejection failure of rock blocks. To reveal the energy evolution patterns and failure mechanisms associated with rock pillar bursts in underground structures (e.g., deep-buried tunnel pillar sections and intersecting tunnels) under high-stress triaxial unloading conditions, a self-developed true triaxial testing system was employed in this study. Given the mechanical characteristics of four-sided free-rock pillars, a series of simulation tests of pillar bursts were conducted at varying confining pressures. Red sandstone specimens measuring 200 mm × 100 mm × 100 mm were used at three confining pressure levels (10, 30, and 50 MPa). The stress path followed was “synchronous loading of triaxial initial stress－rapid bidirectional horizontal unloading－axial stress concentration”, designed to simulate the two-way excavation unloading and stress redistribution process in rock pillars. The failure process, debris ejection velocity, and macroscopic crack propagation were recorded using high-frame-rate cameras, particle image velocimetry. Under a combined first law of thermodynamics and true-triaxial energy calculation method, the accumulation, transformation, and release patterns of total, elastic, and dissipated energies were systematically analyzed, and the role of confining pressure in rockburst energy evolution was clarified. The results show that: (1) Under the triaxial horizontal rapid unloading path, the peak strength of rock specimens exhibits a significant confining pressure effect. The rate of postpeak stress drop increases significantly with higher confining pressure, and the brittle failure characteristics of rockbursts are significantly enhanced. (2) Specimens exhibit considerable plastic deformation and unloading dilation during the unloading stage, a mechanical response difficult to replicate in conventional triaxial tests. (3) A distinct competitive evolution mechanism exists between dissipated and elastic energies across different confining pressure levels. (4) The three types of energy at peak stress in rock specimens progressively increase with the rise in confining pressure, ranking as follows: total energy > dissipated energy > elastic energy.
