Abstract: The boundary dry density (including the maximum and the minimum dry density) is an important parameter affecting the mechanical properties of sand. When the method for determination of dry density in the Chinese specification is applied to the coral sand from the island reefs, the particle breakage of coral sand cannot be ignored during the procedure of measuring dry density, which will introduce great errors to the results. In this paper, the specifications of China, the United States and Japan were adopted to conduct a comparative study of methods for determining the boundary dry density of coral sand. Furthermore, the results of ISO standard sand were compared, thereby proposing a recommended method which was suitable for determining the boundary dry density of coral sand. The results demonstrate that the results of the minimum dry density determined by the three specifications mentioned above are ρ^jis_dmin＜ ρ^GB_dmin＜ ρ^ASTM_dmin  for coral sand and standard sand with different particle sizes; and the maximum dry density results determined are ρ^JIS_dmax＜ρ^GB_dmax ≈ρ^ASTM_dmax . The dry density difference (Δρ_d) between coral sand and standard sand measured by the three specifications varies dramatically with the particle size. With the increase of moisture content, the maximum and the minimum dry densities of coral sand both present the trend of ρ^JIS_d＜ρ^GB_d ＜ ρ^ASTM_d ; and the difference in dry density between different specifications increases with increasing moisture content, and remains stable subsequently. The Chinese specification for particle breakage in the dry density determination process is much larger than the American specification and the Japanese specification. In summary, the determination method of dry density adopted by the American specification has the advantages of clear definition of sand sample state, simple operation, wide range of particle size, ideal dry density results, less particle breakage and small discreteness of dry density results, thus it is a suitable method for the determination of dry density of coral sand.

Key words: coral sand, methods for determination of dry density, particle breakage, moisture content, relative density