Radial stress paths in triaxial tests on compacted Boom clay: stiffness and anisotropy

Abstract

Experimental results of triaxial tests performed on unsaturated soil samples of statically compacted Boom clay are presented. Boom clay samples we re subjected to radial stress paths at two different constant water contents: w= 15%, the as-compacted one, and w= 18%, achieved by vapour transfer technique from the as-compacted condition. The dependence of volumetric compliance on the stress ratio and on the water content is evidenced. The results of the experimental investigation are interpreted in terms of anisotropy of the mechanical response, as a consequence of the induced anisotropy during static compaction, and in terms of the dependence of the compressibility on the micro-fabric of the material. The intrinsic link between the phenomenological soil behaviour and the evolution of its fabric is evidenced, and a normalising variable to take it into account at the constitutive level is proposed.