A modified constitutive model for the behaviour of unsaturated expansive soils has been presented. The essential characteristic of this model is the consideration of a double structure in the soil. Basic swelling and shrinage behaviour of active clay minerals is associated with the microstructure. On the other hand, typical irreversible phenomena associated with rearrangement of pore space can be porperly described through the macrostructural part of the model. Interaction between above-mentioned two parts accounts for some typical features of the behaviour of expansive soils. The model has been cast in mathematical terms using concepts of the theory of hardening plasticity. In orderto check the capabilities of the model, three suction controlled oedometer tests on a higly expansive double-structure clay have been analysed. The comparison has shown that the model is able to reproduce most observed experimental results with fidelity.
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