Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Civil Engineering and Engineering Mechanics


S. Pietruszczak


G.A. Oravas


A mathematical framework has been developed for describing the effects of inherent and induced anistropy in clays. The structure of governing equations permits, in general, the modelling of the sensitivity of soil response to the rotation of principal stress axes. The framework employs a continuum measure of material fabric, which is defines as an implicit function of the spatial distribution of porosity/void ratio. The set of classical functions describing the state of the material is thus enriched by new tensorial functions reflecting the orientation of the fabric. Such a formulation is advantageous over a conventional plasticity approach. It remains physically descriptive, in a sense that, the material response is a function of the specific manifestations of the microstructure. The presented approach is general and its applicability extends to other geological materials, provided the proposed evolution law (Chapter 2) is appropriately modified and the material functions are adequately selected. In its present form, the formulation does not account for irreversibility of both the plastic flow and the evolution of microstructure during histories experiencing stress reversals. However, the mathematical structure of the constitutive relations, as formulated in Chapter 3, is such that those effects can quite easily be incorporated into the proposed framework. A key to full reliability of the proposed concept is a proper verification of the evolution law. The identification of the oriented fabric is not a simple matter and requires the use of complex experimental techniques. Some suggestions in that respect have been made in Chapter 2, where a general procedure for the estimation of the components of the porosity tensor from experimental observations has been proposed.