Abstract: Calcareous sand is the primary fill material used in the construction of islands in the South China Sea. Throughout the process of island construction, the calcareous sand foundation will be subjected to external loads with varying consolidation stress paths, investigating the drainage strength characteristics of calcareous sand under various consolidation stress paths is an urgent requirement in practice. By conducting triaxial consolidation drainage shear tests on calcareous sand samples obtained from a reclamation island in the South China Sea, the evolution of strength parameters and the degree of particles breakage of calcareous sand with varying consolidation stress paths are investigated. The results show that the strain softening and dilation characteristics of calcareous sand diminish progressively as the mean effective stress and the effective principal stress ratio increase. In contrast to isotropic consolidation conditions, when the effective principal stress ratio diminishes to 0.45, the reduction coefficient of peak strength for the consolidated drainage of calcareous sand spans from 0.60 to 0.95. Within the conventional stress range, as the effective principal stress ratio increases, the peak internal friction angle shows a decreasing trend, ranging from 38° to 53°. During the consolidation, the degree of particles breakage increases with the increase of the deviator stress. However, following completion of shearing, the degree of particles breakage paradoxically diminishes, with particle breakage during the shearing phase assuming predominance. The quantitative relationship is verified between the peak internal friction angle and the relative breakage potential under different stress paths. Calculations predict peak internal friction angle values that are approximately 0.8 to 1.2 times the experimentally measured values. Differences in particle crushing caused by varying consolidation stress paths and consolidation pressures are the primary reasons for the differences in the consolidation drainage strength properties of calcareous sand after shearing.

Key words: calcareous sand, stress path, consolidated drainage strength, particle breakage, internal friction angle