An experimental investigation into the mechanical behaviour of a structured stiff clay

In recent years, fundamental research has been carried out into the properties of some natural stiff clays and the corresponding reconstituted materials, highlighting the role of microstructural features in the observed differences. In this paper the results of an experimental investigation into the mechanical behaviour of an Italian stiff clay of marine origin are presented. Medium-pressure and high-pressure stress-controlled triaxial cells were used in which natural samples underwent isotropic and anisotropic compression and swelling before drained or undrained shearing. Comparison of soil behaviour observed after different compression histories up to different values of maximum effective stress allowed the following aspects to be discussed: the effects of the initially structured state on the medium to large strain response and shear strength characteristics of the soil; the relevance of volumetric and deviatoric plastic strain to the structure degradation; the role and implications of the imposed non-isotropic stress histories; the permanent differences between reconstituted samples and fully destructured natural samples; and the uniqueness of the critical state condition.