Development, application and comparison of coupling techniques for modeling the hydromechanical behavior of unsaturated soils

This paper presents formulations for modeling the hydromechanical behavior in unsaturated soils using different coupling techniques. For this purpose, hydraulic constitutive relationships based on classical empirical models and mechanical constitutive relationships based on generalized effective stress are adopted. The coupling terms are defined using fixed stress rates. They are included in finite-element formulations adapted for using four coupling techniques: the fully implicit, the sequential-iterative, the sequential-explicit, and the one-way. The algorithms proposed for each technique are implemented in a numerical framework that manages the solution process considering the same simulator, enabling fair comparisons among all methods. Numerical tests are carried out for each coupling technique's stability, accuracy, and performance. According to the results, the proposed techniques can be adopted to simulate properly the hydromechanical behavior of unsaturated soils, including soil expansion and collapse under wetting.