Abstract: The interaction between the coral sand and structures widely exists in the island-reef engineering practices. Due to the low structural strength and fragility of coral sands, it is prone to the particle breakage under the external loads, resulting in more complicated mechanical properties of the interface. Through the ring shear tests of the coral sand-steel plate interface and the comparison with the quartz sand, the particle breakage evolution, and the particle shape change rule of the coral sand interface after the shear are revealed. The results show that, under the same conditions, the content of small particles produced by the coral sand is significantly higher than that of the quartz sand, and there is a critical vertical pressure of 300 kPa and 200 kPa for the coral sand with 0.5-1 and 1-2mm particle sizes, respectively. When the vertical pressure is higher than the critical pressure, the impact of the vertical pressure on the PSD curve is significantly reduced. The crushing rates of the coral sand and the quartz sand increase with the increase of the vertical pressure. The trends demonstrate an exponential function relationship and linear relationship with the vertical pressure respectively. After shearing, the particle shape develops from the irregular to rounded, and when the vertical pressure is large, the particle shape of the coral sand and the quartz sand is relatively close to each other, and both tend to be rounded.

Key words: Coral Sands, Quartz Sands, Interface, Particle Breakage, Particle Shape