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.