Effect of stress anisotropy on stiffness of clays using bender elements

Abstract

Studying and determination of shear wave velocity and shear modulus of clay has a considerable importance in geotechnical engineering. By concerning the real field situation, the initial shear modulus of soil is an important parameter for a variety geotechnical design applications, especially in small strain dynamics. Several methods and techniques are exists. The technique which is based on propagation of shear wave through soil sample was adopted in this study to measure shear modulus. The shear modulus was measured using a pair of bender elements installed at the top cap and pedestal of the triaxial cell. This research aims are to study variation of shear modulus and shear wave velocity with different stress consolidation (isotropic and anisotropic). The isotropic and anisotropic consolidation was conducted step by step so the variation of shear modulus can be determined. To examine the influence of deviator stress on shear modulus, a number of tests of consolidated undrained triaxial compression tests were performed both in anisotropic and isotropic conditions. There is a unique relationship between shear modulus and mean effective stress for both isotropic and anisotropic consolidated samples. It was found that no discernible effect of anisotropy of stress on the values of shear modulus even at high mean effective stress. The undrained shearing was carried out at the strain rate of 0.02 mm/min, during this steps, the elastic shear modulus was continuously recorded. The shear modulus obtained during undrained triaxial shearing exhibit similar dependency on the mean effective stress. The path of shear modulus during undrained shearing, both from isotropically and anisotropically consolidated samples generally followed the path obtained during consolidations. It implied the negligible effect of the deviator stress on shear modulus. An empirical equation was then proposed to express the shear modulus against mean effective stress for Bangkok clay.