Microscopic mechanisms of coral reef limestone crack propagation

Coral reef limestone (CRL) is a marine sedimentary rock dominated by biogenesis, and its composition as well as internal structure characteristics are different from traditional terrigenous rocks. This article used CT scanning and petrographic thin section observations to visually and quantitatively analyze crack morphological characteristics after triaxial shear failure at a microscopic scale. The analysis revealed the mechanism of crack initiation and propagation from the perspectives of geological genesis and fracture mechanics. Results show that the crack propagation mechanism in the bio-cemented framework includes propagation along crystal boundaries and across crystals. Cracks can be classified as intergranular cracks, transgranular cracks, and bifurcation cracks based on crack morphology. The destruction mode of the specimen is controlled by the pore structure and cemented framework. Based on the pore distribution, the destruction mode can be divided into local tension failure and monoclinic shear failure. Understanding CRL crack propagation mechanisms has important scientific significance and practical engineering value for enriching rock damage theory and long-term stability analysis of island reef engineering foundations.