Evolution characteristics of mesoscopic pore structure for coral sand samples based on CT-triaxial test

The evolution of pore structure during loading has an important influence on the mechanics of coral sand. Using the self-developed high-pressure geotechnical CT-triaxial apparatus, the triaxial consolidated triaxial test of coral sand with a confining pressure of 100-1600kPa was carried out under the premise of ensuring the conventional size of the sample. The real-time CT scanning of the coral sand sample was carried out during loading. The pore shape parameters like sphericity and anisotropy are analyzed according to the CT image, and the evolution of pore structure for coral sand were analyzed by the digital volume correlation method. The results show that the evolution of pore structure for coral sand samples during the loading process can be roughly divided into three stages with the influence of confining pressure and particle breakage. That is the loading end (section I) is mainly affected by compression, the porosity decreases because of particle breakage and movement, and the local strain is mainly negative. While in the middle and below parts of the sample (sections II and III), the slipping particles and increasing porosity macroscopically shows dilatation at low confining pressure, and the local strain shows positive strain. However, high confining pressure and particle breakage inhibit dilatation. It explains that the shear zone of the sand sample often occurs in the middle and lower parts of the sample at low confining pressure. During loading, the pore shape of the specimen becomes closer to spherical and isotropic with the increase of confining pressure, and the deformation of the specimen increases with the axial strain and gradually decreases under the constraint of high confining pressure. The pore volume and local strain of the sample are gradually stabilized during loading. The research results are of great significance for understanding the engineering mechanical properties of coral sand.