Coral sand, as a geological material for foundation filling, is widely used for reclamation projects in coral reef areas. The coral sand is characterized by a wide grain size distribution. A series of centrifuge shaking table tests were conducted to explore the seismic response of a shallow buried underground structure in saturated coral sand and coral gravelly sand. The emphasis was placed on comparing the similarities and differences in the dynamic behavior of the underground structure at the two sites. The responses of excess pore pressure, acceleration, displacement, and dynamic soil pressure of the structure were analyzed in detail. The results indicated that the underground structure in coral sand had a significant influence on the development of excess pore pressure in the surrounding soil, but this effect was not evident in coral gravelly sand due to well-drained channels. Liquefaction was observed in the soil layer around the structure in coral sand, but it did not occur in coral gravelly sand. In coral sand, the liquefaction of the soil layer at the bottom of the structure caused a significant attenuation in the acceleration of the structure. Compared to coral gravelly sand, the acceleration response of the soil layer near the bottom of the underground structure was higher in coral sand. During the shaking, the displacement pattern of the structure in coral gravelly sand was slight subsidence-slight upliftsignificant subsidence, while it exhibited a significant uplift in coral sand. The maximum dynamic soil pressure distribution on the structural sidewalls presented a trapezoidal distribution, and the dynamic soil pressure had a strong connection with the development of excess pore pressure in the surrounding soil.

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.