Abstract: Coral reef-sand mixture is an important supporting layer of infrastructure. To investigate the effect of particle gradation composition on shear strength and dilatation of coral reef-sand mixtures, simple shear tests were performed using fully automatic medium-sized stacked ring direct shear instrument. The tests were conducted on samples with varied P₅ content and water content under four different normal stresses of 50, 100, 200, and 400 kPa. The experimental results show that the shear strength of coral reef-sand mixtures first increases and then decreases with the increase of P₅ content. The shear strength reaches its maximum when P₅ content is 25%-50%. In the shearing process, coral reef-sand mixtures contracted first and then dilated. P₅ content has a significant effect on dilatation, internal friction angle, and apparent cohesion. Water content weakens the shear strength of coral reef sand mixture.

Key words: coral reef-sand mixtures, P₅ content, simple shear test, shear properties, water content