Experimental study on mechanical behavior and particle crushing of coral sand-gravel fill

The coral sand and gravel are used as the main source of reclamation fill in the island construction of the South China Sea. Due to their biological origin, the grains of coral sand-gravel fill are porous and prone to breakage. A series of large-scale compression tests, triaxial drained and undrained shear tests are conducted on a typical coral sand-gravel fill from the South China Sea, and the basic mechanical properties such as compression index, Yang’s modulus, shear-dilatancy and strength parameters as well as particle crushing characteristics of the coral sand-gravel fill are studied. Under the compression, the particle crushing of a loose sample is more serious than that of a dense sample. Particle crushing increases with the increasing pressure, in result, the compressive modulus and Young's modulus increase little, and the peak friction angle and the critical state friction angle decrease significantly as the pressure increases. The particle crushing has a strong dependency on stress path and history. The samples with the same density but different pre-compression histories exhibit significantly different responses under compression. The samples with the same density and initial pressure also show different dilatant tendency and strength characteristics under drained and undrained triaxial shearing. The peak friction angle depends on the stress path and the evolution process of particle crushing, and the critical state friction angle can be well correlated to a particle breakage index in the final state, implying that it is independent of the intermediate evolution process of particle crushing.