Investigation of Low-Amplitude Shear Wave Velocity in Anisotropic Material

摘要

An understanding of the relationship between low-amplitude shear wave velocity and state of stress is necessary for correctly measuring and properly utilizing seismic shear waves in geotechnical engineering. Theoretically, the mean effective stress has been shown to be the stress state controlling shear wave velocity in an isotropic, homogeneous, particulate medium. Mean effective stress has been assumed to be the stress state controlling anisotropic, particulate material even though several researches have shown discrepancies with this assumption. Therefore, a 7-ft cubical sample of dry sand was constructed in a large-scale triaxial device. Instrumentation was embedded in the sample during construction so that shear waves could be excited and monitored within the sand while loaded under true triaxial conditions. Extensive seismic tests were conducted under isotropic, biaxial and triaxial confinements in order to compare measured shear wave velocities with previous research and to investigate the influence of anisotropic stress state on velocity. The behavior of shear waves under isotropic loading agrees with the results of previous investigations and indicates the importance of mean effective stress in estimating shear wave velocity. The shortcomings of the mean effective stress method are clearly demonstrated in the biaxial and triaxial test series. A three-individual-stresses method is shown to be a more correct model for predicting the variation of shear wave velocity under anisotropic stress conditions, as well as being a more sound approach based on stress-strain laws.