The study of the deformation and damage evolution behaviour of surrounding rock under excavation unloading conditions is of vital importance for a deep understanding of the mechanism of roadway failure. In this study, unloading testing using a partially hollow thick-walled cylinder cement mortar specimen with dimensions of 280 mm (height) × 200 mm (outer diameter) × 60 mm (inner diameter) and a solid height of 60 mm at the bottom was performed to investigate the deformation response and damage failure evolution characteristics of the surrounding rock. The experimental results showed that the higher deviatoric stress level accelerated the damage development caused by the unloading effect and improved the expansion rate of the internal cracks, which led to a higher radial strain rate, total strain, and acoustic emission hits. When deviatoric stress increased to a relatively higher level, the radial strain rates were highly unstable, and the surrounding rock near or at the opening free surface was damaged locally and regionally. During the failure process of the specimen, the generation of the deformation and damage in the unloading stage was more alive (as indicated by the growth rate). Nevertheless, the main deformation and damage to the surrounding rock were generated and accumulated in the maintaining stage after unloading.

中文翻译：

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卸荷条件下偏应力对围岩变形和破坏演化的影响

对开挖卸荷条件下围岩的变形和破坏演化行为的研究对于深入理解巷道破坏机理至关重要。在这项研究中，使用尺寸为280 mm（高）×200 mm（外径）×60 mm（内径），底部实心高度为60 mm的部分空心的厚壁圆筒水泥砂浆试样进行卸载测试。进行了研究，以研究围岩的变形响应和破坏破坏演化特征。实验结果表明，较高的偏应力水平加速了卸荷效应引起的损伤发展，提高了内部裂纹的扩展率，从而导致较高的径向应变率，总应变和声发射冲击。当偏应力增加到一个相对较高的水平时，径向应变率非常不稳定，并且靠近或位于开口自由表面处的围岩在局部和区域受到破坏。在样品破坏过程中，卸载阶段变形和损伤的产生更为活跃（如生长速率所示）。尽管如此，卸荷后在维护阶段仍会产生并积累对围岩的主要变形和破坏。