Abstract: The hydraulic sorting effect in the dredger filling process results in uneven distribution of grains with different sizes in the calcareous sand foundation. Because of the formation of fine-grained layer, composed of silt and fine-grained sands with different contents of fine-grained particles, which is uneven distributed and very heterogeneous, it may lead to the bearing capacity and uneven settlement problems of the calcareous sand foundation. In this paper, to study the effect of fine-grained particles content on mechanical properties of calcareous sands, a series of triaxial shear tests under consolidation drainage conditions are carried out on fine sands with different contents of silty-sands. The results show that (1) the dilatancy property and peak deviator stress of soil samples decrease gradually when the content of fine particles increases under the same confining pressure. (2) All these fine sands with a dry density of 1.40 g/cm3, show the strain softening characteristics. The worst stability occurs in samples with 10% content of silty-sands, and it strengthens with the increased content of silty-sands. (3) The particle occlusion effect, makes a non-negligible apparent cohesion in the calcareous fine-grained sands. However, a significant decline in the cohesion occurs due to the decreased particle occlusion effect with the increase in silty-sand content when the fine particles content is less than 40%. Results in this paper can provide references for foundation treatment and slope stability analysis of fine-grained sand layers.

Key words: calcareous sands, silty-sand content, particle occlusion, shear dilation, shear strength