Local Boundary Surfaces of a Loose Sand Dependent on Consolidation Path

Abstract

ABSTRACT In the companion paper of Shibuya et al. (2002), a four-dimensional local boundary surface (4-D LBS) applicable for understanding anisotropic shear behaviour of an isotropically consolidated loose Ham River sand (HRS) has been experimentally established by using four stress parameters : the shear stress, t=(σ'1-σ'3)/2 ; mean effective principal stress, p'=(σ'1+σ'2+σ'3)/3 ; the direction of major principal stress relative to the vertical (=deposition direction), α ; and, the relative magnitude of intermediate principal stress, b=(σ'2-σ'3)/(σ'1-σ'3). In this paper, the results of additional sets of hollow cylinder (HC) tests on the anisotropically consolidated samples are newly presented, and are interpreted after the framework of LBS. Undrained initial anisotropy of the loose HRS when subjected to a consolidation path with the effective stress ratio, K, fixed at 0.5, was manifested in a set of HC tests performed using different, but fixed in each test, α values under the conditions of b = 0.3. The shape of a LBS of the anisotropically consolidated sample was demonstrated in a three-dimensional (t, p', α) space in another set of tests, in which the principal stress directions were continuously rotated in various manners. The undrained LBS of the initially loose samples of HRS which have undrained initial anisotropy and limits the effective stress space to be occupied by any undrained paths, was found to be not unique in shape, but pertinent to an anisotropic fabric formed at deposition and modified throughout the consolidation history which followed. The effects of the consolidation path were highlighted by examining the undrained strength at peak conditions.