Steady States of Residual and Deltaic Sands

A programme of consolidated undrained triaxial shear tests is conducted on two residual and deltaic sands of similar size and different shape. Dry pluviation was used to generate an initial random open packing ahead of isotropic consolidation. Overall, both residual and deltaic sands exhibit a non-flow (NF), strain hardening (HS), dilative response. In absence of fines’ fraction, deltaic sands exhibit some levels of softening. It is tempting to attribute this behaviour to the initial random packing because of aeolian deposition (i.e., dry pluviation). There is a threshold fines’ content below which sand dilates (upon undrained straining) and reaches the USS, and above which sand rapidly loses strength (i.e., structurally collapse) and contracts before dilating towards the USS. Confinement level has a control on this threshold fines’ content if sand is angular enough. The thresholds fines content for residual sand varies between 10 to 30 wt.% (confinement depending). For deltaic sands, the threshold fines’ content happens between 10 to 20 wt.% fines’ contents and collapse is far less sudden.