Abstract: Particle morphology is an important parameter affecting the mechanical properties of coral sand. Studying the multi-scale morphological characteristics of coral sand is helpful to interpret its mechanical properties from the microscopic perspective. Based on the particle dynamic image analysis technology, this study carried out particle morphology scanning and comparative analysis on more than 200 thousand coral sand and terrigenous quartz sand (including artificial broken quartz sand and natural quartz sand) particles in different particle size ranges, and proposed the classification standard of particle shape suitable for coral sand. The difference of particle morphology between marine coral sand and terrigenous quartz sand was revealed from particle shape, roundness and convexity. The findings indicate that: (1) Coral sand is mainly composed of blocky, flaky and bar-shapes particles, taking the elongation ratio and flatness ratio of 0.5 as the threshold for the classification of coral sand particle shape, the accuracy of this classification method can reach 90%. (2) The proportion of blocky particles in coral sand is the largest and the content is more than 50%. With the increase of particle size, the proportion of blocky particles increases, and the proportion of flaky particles decreases, while the proportion of bar-shaped particles basically remains unchanged. With the increase of particle size, the proportion of blocky particles in quartz sand is higher than coral sand, which is determined by the mineral properties of the particles, rather than the weathering and crushing mode of the particles. (3) Artificial broken quartz sand and coral sand have relatively similar particle roundness, and slightly less than that of natural quartz sand. The roundness of blocky particles is the highest, followed by flaky particles and the lowest is bar-shaped particles. Therefore, the roundness of aggregate increases with the proportion of blocky particles. (4) The convexity of coral sand is between 0.85 and 1.00, which is lower than that of quartz sand. With the increase of particle size, the convexity of coral sand decreases obviously, while the convexity of quartz sand changes little.

Key words: coral sand, terrigenous quartz sand, particle shape, roundness, convexity