Effects of loading paths and initial densities on mechanical response and gradation evolution of calcareous sand

Calcareous sand, a distinctive granular material in geotechnical engineering, has garnered significant interest due to its irregular particle shapes, internal porosity, susceptibility to breakage, and critical role in island and offshore construction. Despite its importance, the influence of loading paths on its mechanical behavior and particle breakage remains underexplored. This study addresses this gap through an extensive experimental program, including isotropic consolidation and both drained and undrained triaxial compression tests, systematically varying loading paths and initial densities. The findings demonstrate that the strength and deformation characteristics of calcareous sand are profoundly affected by loading paths, initial densities, and particle breakage. A novel breakage evolution model is proposed, effectively capturing gradation changes under diverse testing conditions. Furthermore, the study quantifies the impacts of these factors on critical mechanical properties, including peak friction angle, dilatancy, secant modulus, and critical state parameters. These results provide a robust theoretical foundation for the development of constitutive models that integrate particle breakage and initial density effects. The insights are essential for optimizing geotechnical designs, enhancing stability, and improving infrastructure reliability in coastal and marine environments, particularly in island and reef development projects.