Directional creep response of anisotropic clays

High water content slurries of a kaolin clay with two different pore-fluid chemistries (flocculated and dispersed) were consolidated under isotropic and anisotropic states of stress to produce bulk samples (blocks with dimensions on the order of 150 to 200 mm) of clay soils with widely differing micro-fabrics. A combination of scanning electron microscopy, optical microscopy, and X-ray diffractometry was used to identify qualitatively and quantitatively the micro-fabric of each sample at various levels of particle organization (individual particles, domains, etc.). Then, cylindrical specimens with dimensions of the order of 30 or 40 mm were trimmed in orthogonal directions from these block samples and tested in undrained creep at different stress levels. The macro-behaviour of these specimens is interpreted in terms of rate process theory, and the parameters in the formulation are correlated with quantitative measures of fabric. For a given stress intensity specimens trimmed in the vertical direction were found to exhibit lower strain rates and larger creep deformations than specimens trimmed in the horizontal direction.