a unified elastoplastic model of unsaturated soil

Soils in many earth structures are often unsaturated. research interest on the behavior of unsaturated soils is growing because of an increasing number of geomechanical problems involving suction effects and multiphase flow. it is, therefore, necessary to understand the suction-induced effects on soils and then to use the appropriate constitutive models for the numerical simulation of such phenomena. this paper presents a framework for describing the mechanical behavior of unsaturated soils. it is an extension of an existing formulation developed originally for saturated soils. the extended framework using effective stress to include the effect of partial saturation. with respect a discontinuity around the intersection of the two discrete yield surfaces of the barcelona basic model (loading-collapse, suction increase), the computer implementation of the bbm becomes a little difficult, to overcome problems at the intersection between the lc and si yield surfaces, a unique smooth yield surface is considered. the unified model for simulating both clay and sand has been developed in this study and can describe the mechanical behavior of soils under different loading and drainage conditions. the proposed model, which use concept of hardening plasticity and reduces to the critical state model when the soil reaches full saturation. the two-yield surfaces concept is applied in order to reproduce smooth transition from pre-peak hardening to post-peak softening and from contractant to dilatant behaviors, which are common shortcomings of more classic models. the implicit numerical integration of the model is briefly discussed. the model parameters have the clear physical meanings and can be easily determined by conventional soil tests. the performance and accuracy of the proposed model have been validated by a comparison with numerical results, those from other unsaturated elastoplastic models and experimental data.