Volumetric strains modify the soil–water retention curve. An easy way to take this phenomenon into account is by means of a percolation model based on the pore size distribution of the material. The model proposed herein is able to simulate the retention curves during wetting–drying cycles. As volumetric deformations modify the pore size distribution, its effect on the retention curves can be easily included in the model. The model is validated by comparing some numerical results with experimental results. This procedure represents an option to create fully coupled constitutive models for unsaturated soils.

To accomplish a proper conception and further modeling of the mechanical behavior of soils, observations at the micro and macro scales need to be merged. The authors believe that the link between scales can be achieved using the effective stress concept. In this paper, we present a model that quantifies the air and water volumes contained within the pores of a solid when their pore pressure is varied. The macroscopic consequences of this are expressed in terms of a single stress that is used to formulate a simple elastoplastic constitutive model to predict volume strains and shear strength of soils.

The simulation of the hydro-mechanical behavior of unsaturated soils is becoming a subject of major importance in soil mechanics. However, unlike the laws governing the behavior of saturated soils, those used to describe the behavior of unsaturated soils still lack of simplicity for common engineering practice. This is why it is important to reconcile saturated and unsaturated soil mechanics and establish a unified theory. In this paper, we use the same strength equation of saturated soils in unsaturated materials and verify that a single failure surface is obtained for any value of suction in wetting and drying paths.

In the past 15 years, different researches have shown that the effective-stress approach represents a simple and precise way to generate fully coupled constitutive models for unsaturated soils. This is so because the influence of the degree of saturation and the hysteresis of the retention curve are implicit in the formulation. Here, an elastoplastic framework for the volumetric behavior of expansive soils based on effective stresses is proposed. The hydraulic behavior of the soil is simulated using a porous-solid model able to reproduce wetting–drying cycles. The porous-solid model is based on the current pore-size distribution (PSD) of the soil. Therefore, volumetric deformations can be related to variations in the PSD. The result is a fully coupled elastoplastic framework based on the equation of the volumetric behavior of saturated soils where the compression index depends on the position and direction of the state of stresses with respect to the yield surfaces. Experimental and numerical comparisons show the ability of the model to simulate the behavior of expansive soils under different stress paths.

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