Abstract: The coral clastic calcareous sand generally consists of the remains of marine organism, which is different from the common quartz sand. It has the characteristics of low strength, irregular shape, internal porosity and easy fragmentation. The axial stress, shearing rate and the sample grain size distribution on the mechanical properties of the calcareous sand were investigated on the coral sand samples from Yongshu Reef, South China Sea. The results indicate that, the calcareous sand has the shear softening property, that is, the strain softening is observed after the stress pasts its peak values. This softening reaches stable after a large strain. With the reduction of the shearing rate and the increase of the axial stress, the sample shear strength will increase and the more particle breakage and the less dilatancy of the sample are observed. With the increase of coarse grains in the sample, the shear strength and the particle breakage increase and reach the peak values at the percentage of particles weight greater than 5 mm of 65.14%.

Key words: Calcareous Sand, Particle Breakage, Shear Strength, Shear Rate, Percentage of Particles Weight Greater Than 5 mm