Relationship between internal void ratio and morphological parameters of carbonate sand

With the advancement of marine geotechnical engineering , increasing attention has been focused on the influence of the particle morphology and internal voids of carbonate sand (CS) on its engineering properties . The purpose of this study was to explore the relationship between the internal void ratio and particle morphological parameters using X-ray computed tomography (CT) scanning and three-dimensional (3D) reconstruction of CS particles with a particle size of 0.5–1 mm. A unique particle-tray mould was designed using 3D printing to avoid over segmentation of images of the watershed segmentation algorithm during 3D reconstruction and to guarantee scanning accuracy. The mould was made of an acrylonitrile butadiene styrene (ABS) resin with a density that differed significantly from that of the CS, which also facilitated threshold segmentation in 3D reconstruction. In addition, an ambient occlusion algorithm was adopted to compute the surface-connected voids and surface recesses of the CS. Based on the internal void characteristics, CS particles were classified into three types: solid, distributed, and spiral. A random selection of 100 particles from each type was analysed to determine the internal void ratio and morphological parameters. The results indicated that spiral-type CS particles exhibited the highest internal void ratio, followed by distributed-type CS particles, whereas solid-type CS particles had the lowest internal void ratio. Distributed-type CS particles appeared in plate-like or flattened forms, spiral-type CS particles were elongated, and solid-type CS particles displayed significant variability in their shape distribution. Furthermore, no significant correlation was observed between the internal void ratio and particle morphological parameters such as elongation, flatness, or aspect ratio. However, a strong correlation was observed between the internal void ratio and sphericity , convexity, and 3D shape angularity group indicator ( SAGI ). Both the sphericity and convexity decreased with increasing internal void ratio, whereas 3D-SAGI increased as the internal void ratio increased. Notably, the internal void ratio, sphericity, convexity, and 3D-SAGI of distributed-type CS particles were significantly influenced by the extent of particle surface smoothing, whereas solid- and spiral-type CS particles were not significantly affected. This study can provide the ranges of CS particle morphology parameters for discrete element method modelling and offer convenience for the calibration of void ratios in the future.