Abstract: The shallow coral reefs are mainly deposited by the calcareous sands and gravels which somewhat special to the conventional geotechnical properties of quartz sands and gravels. The basic mechanical characteristics of the calcareous sands from the surficial part of a coral reef are investigated throughout the conventional consolidation tests and direct shear tests. The results indicate that the void ratios of the calcareous sand are much greater than sands from other origin. Under the increased confining pressures, the void ratios of the samples are slightly reduced with a magnitude less than 10%. A large compressibility of loose calcareous sands and the compression modulus increase with the sand deposition depth. Form a loose calcareous sand deposit in coral reefs, the unit weight usually increases with the depth; however, the shear strength of the calcareous sand is generally constant with depth. More test evident is necessary to verify that relationship between the density and shear strength.

Key words: Calcareous Sand, Void Ratio, Degree of Compaction, Shear Strength