Abstract Rock mass excavation is accompanied by rock deformation during unloading, which degrades the quality of rock mass and significantly affects the safety and stability of rock mass engineering. Taking the excavated rock mass from the dam foundation of Xiaowan Hydropower Station as the study object, long-time single hole acoustic tests (SHAT) were conducted in the dam abutment rock mass, with the changes in the acoustic wave velocity recorded. Then, a new method quantifying the excavation damaged zone (EDZ) was proposed according to the cumulative degradation rate of acoustic wave velocity, and a time-dependency model for evaluating the evolution of the excavation heavily damaged zone (EHDZ) was established. The results indicated that the cumulative degradation rate curves of the wave velocity along the boreholes exhibited significant differences in time and space. The depth corresponding to the inflection point on the curve can be regarded as the bottom boundary of the EHDZ, which could be used to generate time-dependency curves, and demonstrate the spatiotemporal evolution process for the EHDZ. The time-dependency curves can be classified into three categories. The differences between the classified curves are related to the depth of the initial EHDZ (EHDZ0), rock mass elastic modulus (E), and unloading stress (σu). The time-dependency model for the EHDZ evolution process follows a negative exponential function. The EHDZ0 depth, E, and σu can determine the coefficients of the model. The model provides an effective method to predict EHDZ depths at different times after rock mass excavation. The prediction results are of considerable significance for researches on the unloading failure and the selection of rock mass reinforcement, which would ensure the stability and safety of the rock mass engineering during construction and operation.

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开挖损伤区划分与时变变形预测——以小湾水电站开挖岩体为例

摘要 岩体开挖在卸载过程中伴随着岩石变形，降低了岩体质量，严重影响了岩体工程的安全性和稳定性。以小湾水电站坝基开挖岩体为研究对象，对坝肩岩体进行长时间单孔声学试验（SHAT），记录声波速度的变化。然后，提出了一种根据声波速度累积衰减率量化开挖破坏区（EDZ）的新方法，并建立了评估开挖重破坏区（EHDZ）演化的时间依赖模型。结果表明，沿钻孔波速累积衰减率曲线在时间和空间上均存在显着差异。曲线上拐点对应的深度可以看作是EHDZ的底部边界，可以用来生成时效曲线，并演示EHDZ的时空演化过程。时间依赖性曲线可以分为三类。分类曲线之间的差异与初始EHDZ的深度（EHDZ0）、岩体弹性模量（E）和卸载应力（σu）有关。EHDZ 演化过程的时间依赖模型遵循负指数函数。EHDZ0 深度、E 和 σu 可以确定模型的系数。该模型提供了一种有效的方法来预测岩体开挖后不同时间的EHDZ深度。预测结果对研究卸载破坏和岩体加固选择具有重要意义，可确保岩体工程在施工和运行过程中的稳定性和安全性。