Small-strain stiffness of reconstituted clay compressed along constant triaxial effective stress ratio paths

The work described in the paper is an experimental investigation of the effects of anisotropic stress states and histories on the small-strain shear stiffness of reconstituted clays as measured with bender element tests. A brief review is made of previous work dealing with the dependence of small-strain shear modulus on stress state and history in isotropic conditions of confinement, and the rational link that exists between void ratio, e, effective stress, sigma', and overconsolidation ratio, OCR, is considered. Under isotropic stress conditions, only two out of the three variables e, sigma' and OCR are required to describe the dependence of the small- strain stiffness of a clay on current state and history. The same approach proved useful in the analysis of the data from tests with anisotropic stress conditions. The values of the small- strain shear modulus of reconstituted samples compressed along stress paths with constant triaxial effective stress ratios were higher than those measured on isotropically compressed samples. The observed differences increased with increasing stress ratio and could be explained only in part in terms of the smaller void ratios of the anisotropically compressed samples at the same mean effective stress. Simple relationships to evaluate the stiffness indexes of clays that have undergone anisotropic stress histories are proposed.