Can advanced sand-based models predict the behaviour of silty sands? A comprehensive experimental and numerical assessment

This article presents a comprehensive experimental and numerical investigation into the monotonic and cyclic behaviour of five natural silty sands. Based on an extensive laboratory programme comprising drained and undrained monotonic triaxial tests, as well as undrained cyclic triaxial tests, four advanced constitutive models originally developed for clean sands, Hypoplasticity with Intergranular Strain (Hypo+IGS), Sanisand, Hypoplasticity with Intergranular Strain and semifluidized state and fabric change effects (Hypo+ISA-SF), and Sanisand with memory surface and semifluidized state (Sanisand-MSf), were systematically calibrated and validated. The models were calibrated using a combination of automated parameter identification with numgeo-ACT and manual calibration, enabling a consistent assessment of their predictive capabilities. The study represents one of the first comprehensive assessments of these advanced constitutive models for silty sands and investigates how successive developments of hypoplastic and bounding-surface formulations improve the description of stress–strain behaviour, contractancy and dilatancy, pore-water pressure generation, stiffness degradation, and undrained cyclic resistance. The results provide new insight into the constitutive mechanisms required to extend advanced sand models towards silty sands and highlight both the capabilities and current limitations of existing formulations for this important class of geomaterials.