Mesoscopic damage evolution of coral reef limestone based on real-time CT scanning

Coral reef limestone (CRL) is a type of biomass limestone formed by reef-building corals and other biological skeletons. Owing to its complex diagenesis environment, CRL consists of a different composition and structural characteristics compared to other homogeneous rocks. In this study, a series of triaxial compression experiments with real-time computerized tomography (CT) scanning revealed the evolution of fracture damage in CRL. The evolution of crack shape characteristics through three-dimensional reconstruction was visually displayed. Moreover, a calculation method for Poisson's ratio was derived using the CT value. Results indicate that the ratio of crack initiation stress to peak stress in CRL ranges from 60% to 75%, and the residual strength after destruction is high. According to the evolution curve of CT value, the triaxial test process was divided into the compression stage I, damage stage II, and destruction stage III. Under the external load, the compaction and damage law of specimens could be characterized using the characteristic parameters of pores as well as the damage variable D. In the CT value-based rock damage constitutive model, the initial damage factor of CRL ranges from 2.95 to 14.78, which is significantly higher than that of homogeneous rocks.