ABSTRACT: Experimental evidence suggests that a mutual relationship between anisotropy and structure of clays exists. It was hypothesized that development and decay of the structure of clays (called structuralizing and destructuralizing) can be regarded as development of anisotropy and decay of anisotropy (isotropizatiori), respectively. Using this hypothesis, an anisotropic rotational hardening rule was incorporated in the Sekiguchi-Ohta elasto-plastic constitutive model. The subloading surface concept was also introduced to model the plastic deformation inside the yield surface more accurately.
The proposed model provided some rational as well as physical explanations for the experimental facts. Using the proposed model, it was possible to simulate the apparent softening behavior observed in anisotropically consolidated
specimens. For isotropically consolidated specimens, no softening was observed, which is consistent with the experimental data. At the critical state, the undrained shear strength of the anisotropically consolidated specimens was the same as that of the isotropically consolidated specimens, This is due to both specimens having the same soil structure after large shearing. The shape of yield surface obtained from stress probe tests was investigated by simulating the tests with the proposed model. Typical data of the stress probe tests of natural clays shows that the yield surface generally has a smooth elliptical shape. By modeling the rotation of yield surface, the proposed model was capable of simulating this 'apparent' yield surface.

Key words: anisotropic consolidation, anisotropy, constitutive equation, K₀ consolidation, soil structure (ICC: D6)