Hydraulic-Mechanical Coupled Model of Unsaturated Soil Considering Time Effect

Abstract In this study, a hydraulic-mechanical coupled model of unsaturated soil considering the effect of time was established based on unsaturated elastic-plastic theory. The model considers not only the influence of the degree of saturation and viscoplastic strain on soil hardening but also that of viscous volumetric strain on the soil-water characteristic curve. The model could completely describe creep, soil-water characteristics, and mechanical properties of unsaturated soil. The elastic-viscoplastic uniform tangent modulus of the coupled model was derived using an implicit integration algorithm. The user material ( U mat ) subroutine was written using the algorithm so that the tangent stiffness matrix could be exported for finite-element calculations. To validate the correctness of the algorithm and program, the model parameters were obtained from wetting-drying cycles and isotropic compression tests. The program was used to predict creep, mechanical, and hydraulic properties under shearing creep and triaxial compression tests. Comparison of the predictions with the experimental results indicated that the coupled model was able to capture the main features of time-dependent hydraulic-mechanical coupled behavior, including hydraulic and mechanical behavior.