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

Abstract

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.