Cyclic Simple Shear Response of Coral Sand under the Dual Effects of Isotropic Confinement and Normal Stress

Coral sand exhibits distinct characteristics that set it apart from hard-grained siliceous sand, posing unique challenges for the design and construction of offshore foundations. One notable aspect of coral sand is particle crushing. Cyclic simple shear experiments were conducted on coral sand under varying confining pressures, normal stress, and relative density conditions to evaluate its susceptibility to cyclic instability within carbonaceous deposits. The investigation revealed that the variation in shear stress amplitude, influenced by changes in confinement or normal stress, significantly affects the evolution of particle breakage. Shear stress governs the movement of the undrained stress path, dictating whether it tends toward dilation or compression, and accordingly, breakage evolves. Regardless of relative density, cyclic shear resistance reduces with increasing confining pressure. However, medium-dense and dense samples demonstrate similar cyclic shear resistance due to the possible interlocking of angular particle fragments and filling of void spaces. Besides, crushing-induced densification by the fragments influences the slope of cyclic phase transformation, which is otherwise considered unique.