A critical state model for saturated and unsaturated interfaces

Based on the concept of independent stress state variables to consider the impact of unsaturatedconditions, an elasto-plastic critical state constitutive model for saturated and unsaturated interfaces isintroduced in this paper. the proposed model is capable of predicting many characteristics of unsaturatedinterface behavior, such as the dependence of initial tangent modulus, peak shear stress, dilatancy, andultimate strength on matric suction, net normal stress, and the interface state measured with respect to thecritical state line. to this aim, two distinct yield mechanisms are employed in the model. while changein stress ratio generates plastic deformation in the first mechanism, plastic deformations are due to anincrease in net normal stress, decrease in matric suction, or both, in the second mechanism. the presenceof appropriate state dependent ingredients enables the model to provide realistic predictions over a widerange of variations of density, net normal stress, and matric suction. by direct comparison of the modelpredictions with experimental data, the predictive capacity of the proposed model is evaluated.