Shear characteristics of calcareous gravelly soil

Because of its angularity, crushability, and high void ratio, calcareous gravelly soil has peculiar geotechnical properties. A series of large-scale direct laboratory shear tests was conducted on calcareous gravelly soil taken from coral reefs in the South China Sea. This study aimed to investigate the shear characteristics of calcareous gravelly soil under conditions of varying gradation, water content, density, and mineral composition. The experimental results revealed the extremely different mechanical properties of calcareous gravelly soil compared to common non-cohesive soil: calcareous gravelly soil has greater apparent cohesion, larger friction angle, and lower softening value than quartz sand. The friction angle increases with dry density, while the apparent cohesion increases with the median particle size (D (50)) of the soil. After shear failure, the apparent cohesion decreases significantly from the peak value, but friction angle decreased slightly. Grouting can be employed to reinforce foundations and enhance slopes consisting of calcareous gravelly soil at the early stage of shear failure. This study intends to provide reference information for engineering constructions on coral reefs and report new findings on coarse-grained soil.