Abstract: The coda wave propagation path has received extensive attention as it is more sensitive to small changes in the medium than the direct wave. During the process of loading, the wave velocity, medium or source changes may cause the coda wave to change. The physical mechanism of change in the ultrasonic coda wave varies during different deformation stages. Meanwhile, there exist local damages in the rock sample during the deformation, and it will be accompanied by acoustic emission. Combining the ultrasonic coda wave and acoustic emission is beneficial to characterize the coda wave characteristics and damage degree of the sample at different deformation stages. In this paper, three kinds of rocks, including granodiorite, marble and sandstone with the sizes of 50mm×50mm×150mm, are used to carry out observations of ultrasonic coda wave and acoustic emission during the whole process of loading so as to study characteristics of the coda wave at different deformation stages. The major results are given below: 1)There is a good correspondence between the coda wave variation and the acoustic emission evolution process. When the acoustic emission frequency increases, the coda wave changes accordingly. In particular, the coda wave changes in the early stages of increased acoustic emission frequency, which indicates that the early damage information of rock can be obtained by analysis of the coda wave. 2)The physical mechanism of the coda wave change is different in different deformation stages. At the initial stage of loading, there are obvious scatterer changes in the coda wave change; then, in the linear elastic deformation stage, the wave velocity change is dominating; in the late-stage of loading, the scatterer change increases and coexists with the wave velocity change, the scatterer change effect is related with the rock micro-fracture degree, the rock will locally be damaged before rupturing, and the role of the scatterer will be enhanced. 3)With the increase of loading, the amplitude of increase of the wave velocity generally decreases gradually, which is basically consistent with the understanding obtained through the direct wave. The interference of acoustic emission can be eliminated because of the Kaiser effect when analyzing the coda wave. The consistency of the wave velocity change and stress loading and unloading is further verified. 4)The micro-fracture generated during rock deformation will change the physical mechanism of the coda wave change, and the scatterer effect will be significantly enhanced. At the same time, the acoustic emission waveform will cause interference to the ultrasonic coda wave. This means that attention needs to be paid when analyzing rock damage using only coda wave data. In short, the ultrasonic coda wave and acoustic emission can reflect the damage inside the rock, and the change mechanism of the coda wave in different deformation stages is different. The joint observation of the two can play a mutual verification role, which is conducive to improving the reliability of the observation results.

Key words: ultrasonic coda wave, acoustic emission, rock experiment, wave velocity variation, scattering change

摘要： 文中采用尺寸为50mm×50mm×150mm的花岗闪长岩、 大理岩以及砂岩3种不同的岩石样品, 开展了超声尾波和声发射同步观测研究。 结果显示: 1)尾波变化与声发射演化过程存在良好的对应关系, 声发射频度增加时尾波的变化随之改变, 尤其是声发射频度增加的早期阶段尾波便出现变化。 这预示了分析尾波可获得岩石早期的损伤信息。 2)不同变形阶段, 尾波变化的物理机制不同。 加载初期, 尾波变化存在明显的散射体改变特征; 随后, 在线弹性变形阶段则以波速变化为主; 加载后期, 散射体的改变增加, 且与波速变化共存, 散射体的改变效应与岩石微破裂的程度有关。 3)随着载荷的增加, 波速增加的幅度总体呈逐渐减小的趋势, 这与通过直达波获得的认识基本一致。 4)岩石变形过程中产生的微破裂会改变尾波变化的物理机制, 散射体效应将显著增强。 同时, 声发射波形将对超声尾波造成干扰, 因此在仅利用尾波资料分析岩石损伤时需要关注相关的问题。 总之, 超声尾波变化和声发射均可反映岩石内部的损伤情况, 且不同的变形阶段尾波的变化机制不同, 二者的联合观测可起到相互验证的作用, 有利于提高观测结果的可靠性。

关键词: 超声尾波, 声发射, 岩石实验, 波速变化, 散射体变化