This paper describes a study of the virgin compression behaviour of both naturally and arti®cially structured soils under one-dimensional compression or isotropic compression. It is proposed that during virgin compression, the additional voids ratio sustained by soil structure is inversely proportional to the current mean effective stress. The proposed formula has been ver-i®ed for 20 different naturally and arti®cially structured soils, and it is seen that the proposal describes well the behaviour of all these soils. Finally, a general discussion on soil structure and its features is presented, and the proposed compression equation is extended to describe the compression of structured soil along a general stress path.

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A theoretical framework to describe the behavior of natural clay is proposed in a new four-dimensional space, consisting of the current stress state, stress history, the current voids ratio, and a measure of the current soil structure. A key assumption of the proposed framework is that both the hardening and the destructuring of natural clay are dependent on plastic volumetric deformation. Two different assumptions about how this destructuring occurs are proposed, based on which two versions of a complete constitutive model have been formulated. The behavior of reconstituted soil can also be simulated by the proposed model as a special case where the structure of soil has no effect on soil deformation. Characteristics of the proposed model are demonstrated through systematic simulations of the influence of soil structure on clay behavior. The simulated behavior of natural clay is compared qualitatively with widely available experimental data. It is seen that the proposed model successfully represents the main features of natural clays with various soil structures.

SUMMARYThe aim of this note is to quantify the in#uence of soil structure on the compression behaviour of natural soils using the disturbed state concept (DSC). The behaviour of the fully adjusted state is chosen to be that of the corresponding soil in a reconstituted condition so that the disturbance function is a direct measure of the e!ects of soil structure. A new DSC compression model is proposed. This model is able to describe the compression behaviour of structured soils under loading, swelling and reloading. Special versions of the proposed model are also described for situations (a) where the compression behaviour of the corresponding reconstituted soils is linear in the e}ln p space and (b) where the compression is one-dimensional. The ability of the proposed model and its various versions to describe the compression behaviour of structured soils has been veri"ed.

This paper reviews the phenomenon of volumetric hardening, which is a common feature of the mechanical behaviour of many geo-materials. Three di!erent material idealizations have been proposed to describe this hardening, and the paper contains the corresponding mathematical formulation. These idealizations vary in their complexity and hence their ability to capture di!erent aspects of real material behaviour. Any of the three postulates can be implemented into most constitutive models. As a demonstration of their capabilities, the postulates have been implemented into the well-known modi"ed Cam Clay model, and computations are made with the resulting new constitutive models. It is seen that the new models can successfully represent important features of soil behaviour such as plastic yielding associated with loading inside the current virgin yield surface, the loosening or densifying of granular soils caused by shearing, and the accumulation of both volumetric and distortional deformation caused by repeated drained loading over a large number of cycles.