Fractal breakage and particle shape analysis for coral sand under high-pressure and one-dimensional creep conditions

Coral sand is a type of marine biogenic granular material with extremely high calcium content. From the microscopic viewpoint, coral sand grains are characterized as highly angular, irregular in shapes and crushable. One-dimensional creep tests were conducted on coral sand under very high pressure to investigate the evolution of particle size distribution and change of particle shapes caused by particle breakage. Benefited from particle size analysis and shape evaluation with high speed dynamic image analysis apparatus, the evolution of particle shape along with stress was analyzed statistically, and shape factors including aspect ratio, sphericity and convexity increase with increasing pressure. Shape factors for particles with different sizes tend to reach a same value, which illustrated that the morphology of particle after breakage is scale independent and self-similar in this wide range of sizes. This paper analyzed the fractal feature after particle breakage, and found that the fractal dimension increases with increasing vertical stress, and eventually reaches the fractal ultimate breakage (D=2.5). This paper calculated the relative breakage by using Hardin's and Einav's methods, and found that relative breakage is increasing along with increasing pressure. The relative breakage is an exponent function with the pressure, which could be used to predict the relative breakage if the material and pressure are known. The increasing tendency with time is not obvious, because particle breakage is majorly caused by compression instead of creep.