白云岩受压声学特性及其在裂缝研究中的应用

通过实验手段研究了白云岩在三轴和单轴加载过程中的声波波速、幅度、频谱特性的变化特征. 结果发现:(1)白云岩在受压变形过程中,声波波速的变化较好地反映了岩石内部裂缝的闭合、产生、扩展和贯穿等变化. 总体而言,横波波速比纵波能更好地预测裂缝的产生,而纵波对裂缝的非稳定发展或贯穿有较敏感的反映. (2)随着轴压的增大,纵、横波波形的末端都有散射波的出现,且横波波形末端的"鱼尾"状散射波信号更为明显(此时应力点为极限强度的60%左右),预示着岩石内部裂缝的产生和稳定扩展. (3)频谱曲线也很好地反映了岩石内部结构变形情况. 随着岩石受力的增大,频谱曲线上的振幅都呈现增大趋势,标志着岩石的压实阶段;当频谱曲线上低频段较高频段活跃时,标志着裂缝的产生;更有甚者,低频还会取代高频成为主频. (4)在岩石受压裂缝闭合阶段,首波振幅和频谱主振幅都呈现上升趋势;而在裂缝不稳定扩展阶段,主振幅表现出比首波振幅低的上升趋势;振幅曲线达到峰值后都存在一突降拐点,预示着岩石的贯通破坏. 研究对于地层岩石的动态长期监测和工程岩体的稳定性评价都具有重要的理论参考价值. 

THE ACOUSTIC CHARACTERISTICS OF DOLOMITE UNDER COMPRESSION AND ITS APPLICATION IN THE CRACK RESEARCH1)

The variation characteristics of acoustic velocity, amplitude and spectral characteristics of dolomite under triaxial and uniaxial loading are studied by means of the experimental method. The following conclusions can be drawn. (1) During the process of compression deformation of the dolomite, the change of acoustic wave velocity well reflects the closure, generation, expansion and penetration of cracks in the rock. In general, the shear acoustic wave velocity is better than the longitudinal acoustis wave to predict the generation of cracks, while the longitudinal acoustic wave has a more sensitive reflection on the unstable expansion of the cracks. (2) With the axial load increases, the scattered wave signal appears at the end of the longitudinal acoustic wave and transverse wave pattern. And the "fishtail" scattered wave signal at the end of the shear waveform is more obvious (at this point, the axial stress reaches 60% of the limit strength), which indicates the generation and stability expansion of the crack in the rock. (3) The spectral curve is also a good reflection to the deformation of the internal structure in the dolomite rock. As the axial load increases, the amplitude of the spectrum curve shows an increasing trend, which indicates the compaction stage of the rock; when the low frequency signal is more active than the high frequency one in frequency spectrum curve, it marks the occurrence of the crack; what is more, low frequency will replace the high frequency to become the main frequency. (4) In the stage of crack closure, both the first arrival wave amplitude and the principal amplitude tend to increase; while in the stage of unsteady expansion of the crack, the principal amplitude tends to increase more slowly than the first arrival wave amplitude; after the amplitude curve reaches the peak there is a sudden drop point, which indicates the destruction of the rock. The variable characteristic of acoustic propagation displayed during the process of rock pressed makes a good sense to the prediction of rock crack and the evaluation of rock stability. This study has important theoretical reference value for the dynamic long-term monitoring to the rock deformation and the stability evaluation of engineering rock mass.