Mechanical and breakage behaviours of coral sand under three-dimensional stress state

The effect of particle breakage associated with the mechanical behaviour of coral sand has been widely investigated, but not under a three-dimensional stress state with different stress paths and loading directions. In this study, a series of true triaxial tests with different test conditions was conducted for this purpose on two grades of coral sand. Before testing, the particle characteristics of coral sand and particle orientation of the specimen were investigated, showing that the particles have a highly irregular shape, an extremely rough surface and abundant pores, and that the specimen exhibits significant cross-anisotropy. After testing, the particle size variation of coral sand was also analysed to explore the law of particle breakage that incorporates the effects of intermediate principal stress and cross-anisotropy. Test results show that (a) in the constant minor principal stress tests, as the intermediate principal stress coefficient (b-value) increases, the peak deviatoric stress increases and then decreases under drained conditions, but continuously decreases under undrained conditions; (b) coral sand specimens loaded along different loading directions or stress paths exhibit significantly different strength and deformation characteristics; (c) a unique relationship between the relative breakage index and modified input energy is established by introducing a cross-anisotropy correction factor, independent of the b-value and other test conditions.