Mechanical behavior of coral gravel during triaxial test using X-ray computed tomography

Coral soil in large quantities of islands has been used for the construction of islands with the development of global marine construction projects. At present, the research on the macro and micromechanical behavior of coral soil during loading is insufficient, which is related to the development of marine engineering. Using the self-developed high-pressure geotechnical CT-triaxial apparatus, the consolidated drained triaxial tests were conducted on coral gravel under confining pressures ranging from 200 to 800 kPa, all the while employing realtime CT scanning to monitor the sample's deformation. The deformation, particle breakage, and porosity of coral gravel could be directly observed by CT images and its post-processing. The results show that the stress-strain relationship of the samples is strain hardening. Notably, particle breakage during consolidation predominantly manifests as corner breakoff, whereas shearing processes primarily induce splitting. The relative breakage Br is not only approximately linear with the average coordination number C-N of particles, but also with the logarithm of average particle size d, porosity n, and local strain s. Observing the evolution of the sample during loading, the increase of confining pressures leads to the decrease of the sample porosity, resulting in a diminishment in pore dimensions, a densification of particle packing, and the increase of contacts between particles. Consequently, this induces particle breakage and continuous volumetric contraction, thus the stress-strain relationship is hardening. The reciprocal influence between macroscopic and microscopic mechanics manifests in coral gravel. The experimental findings could provide valuable insights for marine engineering construction.