Effect and mechanism of fines content on the shear strength of calcareous sand.

Fine-grained calcareous silt interlayers with a non-uniform thickness are distributed discontinuously in the hydraulically reclaimed foundation of island-reefs in the South China Sea. Because of their high compressibility and low strength, these interlayers commonly cause differential foundation settlement and result in the cracking of buildings, which poses a potential safety hazard. In this study, consolidated-drained triaxial shear tests were conducted to investigate the effect of fines content (FC) on the shear strength of calcareous sand. The brittleness index and dilatancy coefficient were introduced to quantify the strain-softening and dilatancy of calcareous sand. The mechanism by which the FC affects the calcareous sand strength was revealed in terms of the particle shape and soil structure. Under a constant effective confining pressure, an increase in FC led to a gradual decrease in peak strength, a weakening of strain-softening characteristics, less dilation, and a linear decrease in apparent cohesion for calcareous sand. The internal friction angle of calcareous sand peaked at a FC of 10%. Compared with quartz sand, calcareous sand has the more irregular particle shape. An increase in FC weakened the interlocking between calcareous sand particles, which decreased the shear strength. The research results are of great significance for slope stability analysis and for the foundation treatment of island reefs. [ABSTRACT FROM AUTHOR]