عنوان مقاله [English]
Numerous constitutive models have been developed to date based on the effective stress principle to perform \ qualitative and \ quantitative simulations of the hydro-mechanical \ characteristics of \ the \ unsaturated non-expansive soils observed in the experiments. However, the hydro-mechanical behavior of expansive clays has been rarely investigated through the theory of plasticity. The aim of this paper is to simulate the shakedown incident in expansive unsaturated clays under drying-wetting cycles within the framework of a plastic bounding surface model.To achieve the objective, the versatility of the shape parameter of the plastic potential is used: in shakedown phenomenon, the dynamic response of the soil structure is elastic-plastic followed by the recoverable response to the imposed cyclic loading. Hence, during the drying-wetting cycles, as the peak of the plastic potential converges to the horizontal stress path, plastic volumetric strain decreases until there is no further plastic strain and behavior of the soil is purely elastic. The plastic potential shape parameter changes with the number of cyclic loading: therefore, the size of plastic potential reduces and peak of the plastic potential converges to stress path.The role of the suction on the hydro-mechanical behavior of soils is also briefly explained, and effective stress is carefully chosen as the single stress state variable to develop the stress-strain constitutive relationships. A novel method is proposed to determine the effective stress parameter of unsaturated soils from the volume change behavior. In addition, suction plays the role of the hardening parameter in the proposed model besides the plastic volumetric strain.The elastic-plastic relationships of the proposed bounding surface for unsaturated geo-materials are described. The model is calibrated using the experimental data, and the results are discussed in detail. Results of the research show that as stress path gets close to the peak of plastic potential, shakedown occurs by a less number of loading cycles. As a result, different stress histories can postpone or anticipate the shakedown response.