Laboratory Study of the Effect of Stress State on the Elastic Moduli of Sand

摘要

A new laboratory device was built which uses dynamic wave propagation todetermine independently the constrained (M), Young's (E), and shear (G) moduli by measuring the dilational, bar and shear wave velocities, respectively. This device, the multi-moduli testing device, can vary the principal stress, in compression or extension, that is parallel to the longitudinal axis of a cylindrical soil specimen, creating a state of stress in the specimen. Dilational and shear wave velocities are determined using pulse test methods. Bar wave velocity is determined using a longitudinal resonant method in which the first 4 natural frequencies of the specimen are determined. Bar wave velocity is computed from the natural frequencies using a two-step reduction process that begins by computing the phase velocity assuming 1-dimensional motion. The 2nd step uses the 3-D solution for longitudinal wave propagation in an infinite rod to adjust the phase velocities. Resulting values for the bar wave velocity are typically within 5% of each other. Tests conducted on dry, uncemented sand subjected to isotropic and biaxial stress conditions showed that when confined isotropically, all 3 moduli could be adequately described by a relationship involving a constant times the mean effective stress raised to a power ranging from 0.45 to 0.51. M and E tests show that the principal stress in the direction of wave propagation controls or dominates the modulus; principal stresses perpendicular to the propagation direction have more influence on E than M. (MM)