The particle shape of coral sand is a crucial factor that affects its accumulation characteristics. Two-dimensional particle images of coral sand with different particle sizes were obtained through optical imaging, and the basic size parameters of particles were measured by digital image processing. The particle shape parameters were created, and on this basis, the variation of shape parameters with size, the distribution characteristics, and the sensitivity of shape parameters were analyzed by mathematical statistics and the fractal theory. In addition, a comparative analysis was conducted for the particle shape and bulk density of coral sand and quartz sand with the same particle size. The results show that (1) for coral sand with particle size ranging from 0.5 to 5.0 mm, as the particle size augments, its overall profile coefficient grows, while the flatness, angularity, and roughness diminish and the particle shape deviates more from the regular circle. (2) The shape of coral sand particles exhibits good fractal characteristics, and the particle shape gets more complex as the particle size grows as evidenced by the fact that the fractal dimension enlarges. (3) All the shape parameters obey a skewed distribution. Concerning the sensitivity to the change in particle shape, the flatness occupies the first place, the overall profile coefficient and angularity come second, and the roughness ranks third, accordingly. It is suggested that flatness should be preferred as the evaluation parameter of the particle shape. (4) Compared with that of quartz sand, the particle shape of coral sand is more irregular, and the intergranular pores are larger under the same accumulation conditions, which is the primary reason why the specific gravity of coral sand is greater than that of quartz sand while the bulk density is smaller than that of quartz sand.

It is commonly accepted that the macroresponse of soil depends significantly on the microscopic particle characteristic features, such as size, shape, and roughness. These parameters can be obtained readily by dynamic image analysis of each individual particle, enabling the quantification of particle morphologies. This study investigated the variation of calcareous sand morphology before and after the one-dimensional normal compression. The tests employed a large oedometer cell (231.6-mm inner diameter and 155-mm height) and coarse calcareous particles (10–20 mm). It was found that samples of different particle shape mixtures have almost the same compressibility due to continuous breakage and gradual fining of coarse sand particles. The particle breakage can be effectively quantified by the change of total particle perimeters in the dynamic image analysis. The mixture of branched particles in blocky sands can effectively increase the particle breakage factor because the branched structure can be easily crushed due to localized stresses during the compression. The breakage of coarse particles can produce a large number of fine particles with an exponential frequency distribution (by number). These fine particles generally are more elongated and flatter than the coarser particles. After the compression tests, all particles tended to be slightly smoother and more spherical, due mainly to the particle asperity damage. In particular, the rounded (spherical) particles were much smoother than the angular ones. The relevance of particle morphology change to geotechnical engineering practice also is established.

Calcareous soil is widely distributed throughout tropical areas. Due to its unique sedimentary environment and soil behaviors, severe engineering problems and disasters have occurred in many regions. To understand the differences in the mechanical properties of calcareous soils in different regions, material composition, physical and mechanical properties of calcareous soils, including specific gravity and void ratio, compression properties, shear properties, and strength properties, were analyzed. The relationship between the sedimentary environment, material composition, and mechanical properties of calcareous soil was examined based upon the results. Results show that the calcareous soil in the South China Sea has a high calcium carbonate content, large particle size, high compressibility, and low bearing capacity, while sand from the Kish Island in the Persian Gulf and Agami sand from Egypt have low compressibility and high bearing capacity. In the South China Sea, Calcareous soil is more difficult to crush than those from the Hormuz Island and Bushehr Port in the Persian Gulf, Dog’s Bay in Ireland, and Quiou in France. Overall, calcareous soils from various locations exhibit significant differences in properties based upon their physical traits. It is suggested that the influence of sedimentary environment and geological conditions should be considered in engineering constructions.