Abstract: The complexity of the mechanical behavior of the coral reef limestone induces challenges to the construction of the projects for the Belt and Road Initiative and the Maritime Silk Road. In this paper, the damage evolution characteristics of the coral reef limestone under the variable amplitude cyclic loading are quantitatively evaluated based on the in-situ CT scanning triaxial test equipment. The structural changes of the coral reef limestone under different stress conditions are studied by the CT scanning and the digital image analysis technique. The results show that the secant modulus of the coral gravel limestone increases first and then decreases with the pressurization and evolution of the damage, while the elastic modulus decreases in the pressurization stage. The stress concentration occurs at the tip of inner pores of the coral reef limestone under the external load, and cracks expand first in the area with the largest porosity and the most complex pore structure. According to the distribution characteristics of cracks in the three-dimensional space and the slice analysis, the specimen under the cyclic load of 6 MPa occurs the tension-shear failure mainly with the shear. The research results provide a reference for the security and stability evaluation of surrounding rock in island and reef engineering construction.

Key words: CT Scanning, Cyclic Loading and Unloading, Coral Reef Limestone, Pore Network Model, Layer-by-Layer Porosity