Mechanical behavior and particle breakage of calcareous sand in triaxial test

Calcareous sands typically have wider ring grain shapes, significant intragranular porosity, complex structure, and lower grain hardness, which pose a risk when used as the foundation, breakwaters, and backfill material in construction. Hence, the calcareous sand was subjected to multiple triaxial shear tests under different confining pressures. Firstly, the triaxial test is conducted under confining pressure of 100-1200 kPa to investigate the effect of confining pressure on the shear characteristics. It noted that more contraction with confining pressure increases caused by the easy breakage of particles under a high confining pressure. Then, the grain size distribution test is conducted to characterize the particle breakage with the results of grain size distribution curves and relative particle breakage index. A linear relationship is established between relative particle breakage index and confining pressure. Secondly, the results of triaxial test are analyzed to investigate the mechanical behavior, volumetric behavior, and strength parameters. The dilative volume or pore water pressure changes are most pronounced at low confining pressure and high-stress levels approaching failure. In addition, an equation is defined to describe tangential stiffness modulus evolution. The effect of confining pressure was converted to relative particle breakage index to illustrate the tangential stiffness modulus evolution better.