Vibration Modulus of Normally Consolidated Clay

The resonant-column technique was used to measure the vibration shear modulus of a normally consolidated kaolinite under various anisotropic states of stress. The effects of the deviatoric and isotropic components of stress, void ratio, and other secondary effects are studied. Data from these tests along with other previously published test results for other clays with different structures lead to the following conclusions: (1) The vibration shear modulus is independent of the deviatoric component of ambient stress (octahedral shear stress); (2) the vibration shear modulus decreases with increasing void ratio and Eq. 4 in the paper is a fair representation of the effect of void ratio; the effects of structure seem to be mostly accounted for by the void ratio parameter; (3) considering the isotropic component of ambient effective stress (effective octahedral normal stress), σ¯0, as an independent variable, and not including the effects of void ratio and secondary time effects, the vibration shear modulus varies with σ¯0 to the 0.5 power; and (4) there is a secondary increase of the vibration shear modulus with time, at constant effective stress, not accounted for by changes in void ratio. This stiffness build-up is sensitive to particle disturbance and can be partially or totally destroyed by changes in effective stress. This effect may be quite important for soils in situ.