Effects of fines content and density on the static behaviour of silty sand

Silty sand in the offshore Yuedong area exhibits static mechanical behaviour strongly influenced by fines content (FC) and density. To characterize this behaviour and inform geotechnical design, a series of monotonic triaxial compression tests under drained and undrained conditions was conducted on reconstituted Yuedong silty sand with FC from 0–50%. The results show that increasing FC consistently reduces the shear strength and friction angle with no evidence of a threshold fines content (TFC) for strength minima within the tested FC range of 0–50%, which is believed due to the low particle size ratio of the Yuedong silty sand. A high FC suppresses dilatancy and increases liquefaction susceptibility under undrained conditions. The mechanical behaviour is governed by the interaction of FC and void ratio (e0). All specimens ultimately converged to a unique critical state line, indicating a constant critical state friction angle (∼31°) independent of fines content. Crucially, the CSL in the e–log p′ plane shifts downward with increasing FC, resulting in a growing state parameter (ψ = e−ecs) and reduced dilatancy potential at the same void ratio. These findings demonstrate the applicability of the critical state soil mechanics (CSSM) framework to high-FC silty sands, and unify the influence of FC, e0, and stress level into a coherent interpretative model. This study advances the fundamental understanding of silty sand behaviour and provides valuable guidance for strength parameter determination and geotechnical design in Yuedong silty sand and similar materials.