Hypoplastic Modeling of Sand Considering the Time Effect

In this chapter, a newly constructed constitutive model is presented for modeling the time-dependent behavior of granular materials. The model consists of dividing the stress tensor into an inviscid stress using a hypoplastic formulation and a viscous stress with a high-order term representing the strain acceleration. Then, different laboratory tests on granular soils are simulated to evaluate the model performance, i.e., a series of constant strain rate triaxial tests and a stepwise strain rate triaxial test on Toyoura sand, a stepwise strain rate triaxial test on Chiba gravelly soil, and creep tests under different stress levels on Toyoura sand. Comparisons between the experimental and numerical results show the capability of the model in describing the strain rate and acceleration effects, as well as the creep behavior of granular materials. Moreover, the coupling between the inviscid stress and viscous stress enables the evolution of the strain rate increase in the creep tests. Consequently, the three stages of creep, namely, primary, secondary, and tertiary creep, can be well described. Finally, the model, named HYPOSAND, is presented in the ErosLab platform as a practical exercise.