ABSTRACT
Binary materials are sand-fines mixtures where the mechanical behaviour transitions from a configuration where the entire forces are transmitted between the grain contacts (no fines) to an array where all voids are filled with fines and contribute to the force transmission. The fines content controls this complex transition, and as such, it has been incorporated into the definition of the equivalent void ratio concept. The macromechanic modelling of sand-fines mixture soils is challenging. Conventional constitutive models are formulated and calibrated either to work for granular or fine-grained soils. This article presents an application of the boundary surface plasticity model proposed by Dafalias and Manzari in 2004, incorporating the equivalent void ratio concept. The model is tested with a series of monotonic triaxial results on Vietnam silica sand and non-plastic fine sand mixtures. Investigations about the inclusion of the equivalent void ratio as a promising option to model binary mixtures before undertaking substantial changes in the structure of well-established constitutive models are explored. Recommendations on the critical void ratio line based on the experimental observations are also provided.
