Mechanical behaviors of coral sand and relationship between particle breakage and plastic work

As a special geotechnical material, coral calcareous sand (CCS), also widely known as coral sand or calcareous sand, surely has similarities and differences in mechanical behaviors with terrigenous sand. As the foundation material of some important structures such as ports, aircraft runways, and marine lighthouses in the South China Sea (SCS), it is necessary and has engineering significance to study its basic mechanical properties. Taking the CCS sampled from a reclaimed land on the top of a natural coral reef in the SCS as the typical case, a series of drained and undrained triaxial shear tests were performed under conventional and high confining pressure in this study. It is found that CCS has all the characteristics that all granular materials should have. However, since the irregular particle morphology and high roughness particle surface, CCS presents a great initial shear stiffness which is significantly different from that of quartz sand. Only some CCS specimens can strictly reach the critical state, and the feature lines in the p'-q space, i.e., critical state line, and phase transformation line are not affected by the factors such as the consolidation confining pressure, initial dry density, and drainage condition. However, the critical state line in the e-lnp' space is not unique, but dependent on the initial dry density. Based on the particle breakage measurement, a new description for the relationship between particle crushing and plastic work is proposed. It could provide an experimental basis for the development of a constitutive model considering the particle breakage for CCS.