Study on the micro-mechanical behavior and pore structure evolution mechanism of coral reef limestone based on digital rock core

Coral reef limestone (CRL) is a type of marine carbonate rock that exhibits a highly developed pore structure. The pore structure exerts a considerable influence on the mechanical behavior and damage fracture process of CRL. In order to study the micro-mechanical behavior of CRL and its pore structure evolution mechanism, this paper is based on the digital core model of CRL obtained from CT scanning. The two-way transformation method of digital core – finite element model is employed to simulate and analyze the micro-element physical–mechanical behavior of porous CRL under quasi-static compressive loading. The mechanical parameters of the CRL skeleton were obtained through microphysical and mechanical experiments, and the HJC model parameters of the skeleton matrix were determined. This revealed the complex fracture mechanism of the CRL under the influence of pore structure. The study demonstrates that the CRL skeleton is primarily composed of aragonite, exhibiting an average elastic modulus of 76.97 GPa. The applicability of the HJC intrinsic model and its parameters is validated through nanoindentation simulation. The damage process of CRL is characterized by complex stress concentration, stress redistribution, and pore-induced fracture. The evolution of fracture extension is primarily influenced by the processes of pore closure, particle crushing and rearrangement, and micro-fracture initiation and propagation. The evolution of porosity is predominantly affected by the same factors, as well as the formation of micro-fractures and the expansion of existing ones. The non-uniformity of pore structure gives rise to the pronounced anisotropy and inhomogeneity observed in damage fracture.