Abstract: Coral sand, as an important building material of ocean reef islands, is widely used in hydraulic reclamation and construction of military and civil facilities such as island foundation, subgrade, airport runway, etc. A series of laterally confined compression tests were conducted on the coral sand from a reef island in the South China Sea. The effects of particle size distribution and passive confining pressure on the laterally confined compression properties of coral sand were studied quantitatively to provide reference for subsequent research on particle size and passive confining pressure effects of coral sand. The experimental results show that the axial engineering stress-strain curves of coral sand under passive confining pressure exhibit increasing hardening. The stress path of coral sand under laterally confined compression is basically independent of the particle size, and the passive confining pressure increases linearly with the increasing axial stress, which is about 35% of the axial stress. This paper calculates accurately the yield strength and compressibility coefficient of coral sand, the following conclusions are drawn: as the mean particle size of coral sand increases, the yield strength decreases exponentially, while the compressibility coefficient increases exponentially. Therefore, the onset stress of particle breakage is lower for the coral sand with a larger mean particle size, which leads to a higher amount of particle breakage, and higher compressibility as well for the coral sand. The yield strength of coral sand is almost independent of passive confining pressure, but depends only on the material characteristics of coral sand. With the increase of passive confining pressure, the compressibility coefficient of coral sand decreases significantly. This is because the high passive confining pressure prohibits particle breakage of coral sand, and leads to a lower compressibility of coral sand.

Key words: coral sand, particle size, passive confining pressure, quasi-static compression, yield strength, compressibility coefficient