A hydro-mechanical constitutive model for unsaturated soils considering hydraulic hysteresis based on coupled elasto-plastic formulation

Successful prediction of unsaturated soil behavior is quite complex since the simultaneous effects of net stress and matric suction on the degree of saturation and void ratio should be taken into account. Although a large number of constitutive models have been developed to capture the hydromechanical behavior, these models either lack sufficient accuracy to simulate the constitutive behavior of unsaturated soils or are based on complex formulations that affect the accuracy of the results. Therefore, consistent theoretical models supported by efficient algorithms are still needed to understand the hydromechanics of unsaturated soils. In this study, a hydromechanical model based on elasto-plasticity including hydraulic hysteresis has been developed. The proposed model is based on a simpler but powerful mathematical formulation compared to similar models of its kind. The model requires material parameters that require a small number of triaxial experiments to obtain. The study particularly focuses on the effect of the change in void ratio on the water retention behavior. In the integration of the model, an efficient explicit integration algorithm is developed in which a series of unsaturated triaxial tests are simulated at constant suction and constant water content under various net stress and suction traces. Validation analyses have given good results indicating the capability of the proposed model for unsaturated soils.