Study on the mechanical properties and fracture characteristics of dry and saturated coral reef limestone under impact loading

Accurately evaluating the dynamic mechanical properties of coral reef limestone (CRL) is crucial for the safety and stability of island underground engineering structures. A Split Hopkinson Pressure Bar (SHPB) testing system was employed to conduct dynamic impact tests on four different types of CRL under dry and saturated conditions. Additionally, CT scanning and three-dimensional (3D) reconstruction techniques were used to characterize the pore structure of the CRL samples. The results indicate that the dynamic parameters, energy dissipation density, and fracture morphology of CRL are positively correlated with the loading rate. The dynamic compressive strength, dynamic elastic modulus, and energy absorption capacity of the saturated samples are all lower than those of the dry samples. Damage in CRL typically occurs along biocomponent boundaries with poor cementation and areas with abundant through-pores. For dense types of CRL (RW and RD), damage primarily involves skeletal expansion and penetration, exhibiting brittle splitting failure modes with blocky fracture patterns. In contrast, loose types of CRL (CW and CP) primarily undergo perforation propagation, exhibiting crushing failure modes with strip-shaped debris formed along coral growth lines. This study provides valuable insights for the application of CRL in island underground engineering projects.