Effects of fine content on the mechanical properties and breakage behavior of gap-graded coral sand

Hydraulically filled coral sand foundations are susceptible to various challenges within intricate marine environment. The friability of coral sand results in the production of large amounts of sub-graded fine particles under external stress. Meanwhile, the continual influence of oceanic forces leads to a gradual erosion of these fine particles from soil. The interaction between these two long-term effects plays a crucial role in particle breakage and soil mechanics of coral sand. To address this issue, consolidated drained triaxial tests and sieving analysis were conducted on the gap-graded coral sand with various fine contents. Three unique test methodologies are devised to alter the fine content, including hydraulic scouring, particle removal and particle replacement. The experimental results revealed that a specific amount of fine particle loss can significantly deteriorate the mechanical properties of dense coral sand. By replacing coarse particles with fine particles, larger strength parameters and less dilation were observed, yet there existed a critical threshold of 60% fine content, beyond which further substitution did not yield additional improvement in soil strength. Particle crushing was primarily concentrated in the middle layer of the specimen, influenced by the development of the shear band. Furthermore, the amount of newly generated finer particles exhibited a positive correlation with the increase in fine content in the initial gap-graded soil. These findings could enhance the understanding of the role that fines plays in determining the mechanical characteristics and particle breakage behavior of coral sand, and thus aid in more accurate assessments and designs of engineering applications involving coral sand.