Effects of Structural and Stress Anisotropy on Velocity of Low-Amplitude Compression Waves Propagating Along Principal Stress Directions in Dry Sand

摘要

A 7-ft cubical sample of dry sand was tested using the triaxial device constructed by Kopperman et al (1982) and Knox et al (1982). The sand was the same as that used by Kopperman and Knox. A new raining device was fabricated and used to construct this sand sample which resulted in a more uniform sample than prepared earlier. Improvements were also made to the excitation ports in order to have better control. Extensive tests were performed under the following different stress states: isotropic, biaxial and triaxial. In each case, velocities of P-waves propagating along all principal stress directions were measured. Results from these tests lead to the following conclusions: (1) the effect of stress history on P-wave velocity is negligible, (2) the sample can be treated as a cross-anisotropic material under isotropic confinement due to structural anisotropy, (3) complete anisotropy resulted by the coupling of stress anisotropy and structural anisotropy, and (4) P-wave velocity depends on the principal effective stress in the direction of propagation with principal stresses perpendicular to the direction of propagation having a negligible effect on velocity.