Experimental study on the mechanical behavior and particle breakage characteristics of hydraulic filled coral sand on a coral reef island in the South China Sea

Coral sand is the only material for island land reclamation. Due to its special marine biogenesis and porosity structure, coral sand particles are easily crushed at normal level of engineering stress. In this study, drained triaxial shear tests were carried out on coral sand retrieved from a reclamation reef in the South China Sea to study the evolution law of the strength, deformation and particle breakage properties of coral sand with different levels of compaction and confining pressure. The comparative analysis of shear strength index is made between current study and previous investigations. The results show that strain softening and dilatation tendency of coral sand gradually weaken with an increase in confining pressure and decrease in compactness. Within the normal confining pressure range, the values of the peak and critical state frictional angles of coral sand were 33o?58o and 28o?47o, respectively, both of which decreased with an increase in the confining pressure. The relationship among the secant modulus E50, relative compaction and effective confining pressure for coral sand was established. The relationship between the peak friction angle of coral sand and the modified relative breakage index (Br*) can be fitted by a power function equation with a negative index. When the extent of particle breakage is large, the decreasing trend of peak friction angle with an increase in the modified relative breakage index slows down. The correlation between the modified relative breakage index and plastic work for coral sand could be simulated using hyperbolic curve, and it is hardly affected by density. The research results can provide useful reference and technical support for island reclamation and infrastructure construction in the South China Sea.