A micromechanics-based model for sand-silt mixtures

Experimental observations have shown the significant impact of fines or coarse grains on the behavior of sand-silt mixtures. To describe the behavior of sand-silt mixtures under both drained and undrained conditions, this paper presents a mathematical model based on a micromechanical approach. The novelty of this model is the introduction of the equivalent mean size and the evolution of the position of the critical state line with fines content for various sand-silt mixtures. The predictive capability of the model was evaluated by comparing the model simulations with experimental results on undrained triaxial tests of Foundry sand-silt mixtures with fines content, fc = 0–100% and Ottawa sand-silt mixtures with fines content fc = 0–50%, and on drained triaxial tests of Hong Kong Completely Decomposed Granite (HK-CDG) mixtures before and after erosion. The predicted local behavior in the contact planes has also been examined. It shows that all local contact planes are mobilized to different degrees in terms of local stress and strain and that a few active contact planes contribute dominantly to the deformation of the assembly, leading to an anisotropic global behavior when the soil is subjected to external loading.