Constitutive modeling the undrained behaviors of sands with non-plastic fines under monotonic and cyclic loading

In recent years, some unified critical state compatible (UCSC) frameworks have been established for constitutive modeling of both clean sand and sand with various quantities of fines. In existing UCSC frameworks, the equivalent granular void ratio e (R) and equivalent granular state parameter psi (R) are used instead of the void ratio e and state parameter psi to define the soil state and density state, respectively; this enables existing UCSC frameworks with the capability of constitutive modeling of sands with various quantities of non-plastic or low plasticity fines using a unique set of model parameters. However, existing UCSC frameworks cannot be applied to cyclic loading. This study proposes a UCSC framework by merely substituting e (R) and it; for e and psi into the equations of a stress-ratio controlled state-dependent plasticity model that includes cyclic loading simulation capabilities. The proposed UCSC framework is implemented in a fully coupled dynamic effective-stress finite element procedure. The simulative capability of the proposed UCSC framework is evaluated by comparison of the model predictions with existing experimental data of triaxial tests under monotonic and cyclic loading. Moreover, the effects of the fines content on the cyclic resistance ratio and the characterization of liquefaction susceptibility of sandy soils are investigated.