Stress-dilatancy behavior of marine coral sand incorporating non-plastic fines

The existed understanding of stress-dilatancy behavior is predominantly based on experiments conducted with clean quartz sand, with limited research focusing on coral sand. Particularly, impacts of fines and density state on stress-dilatancy response of marine coral sand is of significant concern. This work presents a systematic investigation into these issues through meticulously controlled geotechnical tests, coupled with corresponding discussion and interpretation. Results show that at a high stress level, both pure coral sand and its mixtures consistently undergo shear contraction regardless of fines proportion and density state. However, mixtures with minimal fines experience shear contraction initially, followed by dilatancy under a medium-low stress level. Friction angle at peak state (${\phi }_{\mathrm{ps}}$) and critical state (${\phi }_{\mathrm{cs}}$), excess friction angle (${\phi }_{\mathrm{ex}}$), and maximum dilatancy angle (${\psi }_{\max }$) decrease powerfully as increasing fines content. Besides, the lower and upper limits of variation for ${\phi }_{\mathrm{ps}}$, ${\phi }_{\mathrm{cs}}$, ${\phi }_{\mathrm{ex}}$ concerning ${\psi }_{\max }$ were presented. Correlation between ${\phi }_{\mathrm{ex}}$ and ${\psi }_{\max }$ highlights that Bolton's stress-dilatancy equation, developed for pure sand, remains applicable provided that fines content remains below the threshold value. Additionally, gray correlation result suggests that fines post the dominant influence on above behaviors, followed by density state and stress level. Finally, potential mechanism behinds the influences of fines and density state was explored from the view of particle column buckling.