Underground excavation usually results in the decrease of horizontal stress in the front of the working face, which may trigger the occurrence of rock bust hazards. Examining rock failure under confining pressure unloading conditions is necessary to reveal the fracture mechanism of rock mass subjected to stress disturbance. Although many investigations have studied the rock mechanical behaviors during unloading, the time-lagged triaxial unloading paths on the rock fracturing mechanisms are still poorly understood. Triaxial unloading experiments and the post-test CT scanning technique were conducted on fine-grained marble samples under different unloading conditions. The stress–strain behaviors, energy evolution characteristics, and the fracture pattern of samples were analyzed. The results indicate that obvious features at various stages can be identified from the deformation history curve of the elastic strain energy (U_e), total strain energy (U), and dissipated energy (U_d). U, U_e, and U_d almost all increase with sample deformation at the time duration stage, and the elastic energy and dissipation energy curves slightly decrease and increase again. After the unloading point, the dissipation energy sharply increases and the incremental rate of elastic energy becomes lower. The elastic strain energy increases with the increasing unloading rate for samples at the confining pressure unloading point and failure point, and it is influenced by the time-lag effect of confining pressure. The crack pattern in the CT images depends on the triaxial unloading rate and time effect, which is in good agreement with the energy dissipation and release analysis. The unloading strategy has an effect on the energy conversion during triaxial unloading tests; in other words, energy dissipation and release are dependent on the unloading rate and time.

中文翻译：

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使用能量分析和事后CT可视化，时滞卸载路径对大理石断裂行为的影响

地下开挖通常会导致工作面前部的水平应力减小，这可能会触发岩爆危险。为了揭示受应力扰动的岩体的断裂机理，必须在限制压力卸载条件下检查岩石破坏。尽管许多研究已经研究了卸岩过程中的岩石力学行为，但对岩石压裂机理上的时滞三轴卸矿路径仍然知之甚少。在不同的卸载条件下，对细粒大理石样品进行了三轴卸载实验和测试后的CT扫描技术。分析了样品的应力-应变行为，能量演化特征和断裂模式。U _e），总应变能（U）和耗散能（U _d）。U，U _e和U _d随时间的变化，几乎所有样品都随样品变形而增加，而弹性能和耗散能曲线则略有减少并再次增加。在卸载点之后，耗散能量急剧增加，而弹性能的增量速率降低。在围压卸载点和破坏点，样品的弹性应变能随卸载率的增加而增加，受围压滞后效应的影响。CT图像中的裂纹模式取决于三轴卸载速率和时间效应，这与能量耗散和释放分析非常吻合。卸载策略会影响三轴卸载测试中的能量转换；换句话说，能量的消耗和释放取决于卸载速度和时间。