Novel particle reconstruction and tracking algorithms to reveal 3D micromechanical behaviors of coral sands

The micromechanical behaviors of coral sands remain poorly understood, primarily due to the inherent complexity of their highly irregular particle shapes, which pose significant difficulties for accurate three-dimensional (3D) particle reconstruction and tracking using X-ray tomography (µCT). To address these challenges, this study proposes a novel framework that integrates large vision models and discrete label optimization for efficient and accurate 3D particle reconstruction with optimal transport for robust particle tracking. This framework effectively resolves tracking both particle breakage and internal voids in coral sands, as validated by in situ mini-triaxial µCT tests. Compared with the state-of-the-art method, the proposed approach achieves comparable reconstruction accuracy (90%) while reducing computational time by 50%. For particle tracking, accuracy between adjacent µCT scans (corresponding to axial strain increments of 2.5%, 5%, and 10%) reached 95%, 86%, and 71%, respectively. Micromechanical analysis of coral sands further reveals that heterogeneous local shear deformation develops as axial strain increases, forming an X-shaped shear band. Significant fabric anisotropy emerges after peak stress, with preferred orientations aligning with the shear band. Moreover, particle breakage was observed to occur primarily during the strain-softening stage. Splitting induced by stress concentration was the predominant failure mode.