Experimental study on the effect of fines on the maximum dynamic shear modulus of coral sand in a hydraulic fill island-reef

The reef reclamation field survey results indicate that grain size distribution curves of coral sand in partial regions of coral ground layers, composed of coarse-grained and fine-grained particles in different proportions, are quite wide. Moreover, grasping the dynamic properties of coral sand in South China Sea where earthquakes frequently occur is significantly important for ground response analysis of reclamation reef islands. A series of resonant column tests were performed on coral sand-fines mixtures to investigate the influences of the density, the confining pressure and the fine content on their dynamic characteristics at small level strain in this study. The study employs the tamping energy method to prepare the coral sand-fine mixtures at different densities. The results indicate that the maximum dynamic shear modulus increases with increasing the density and the confining pressure. Under the same test condition, the maximum dynamic shear modulus decreases with increasing the amount of fines, due to that the presence of fines between coarse grains changes the contact condition between grains and the skeleton structure. The traditional expression of the void ratio has no capacity of describing the “real” compaction state of coral sand-fine mixtures and characterizing the role of fines in contributing the skeleton structure of sand. Based on the concept of the equivalent skeleton void ratio, an experienced model jointly considering the effects of the fine content, the density and the confining pressure is proposed to estimate the maximum dynamic modulus of coral sand-fine mixtures. This study is expected to provide a database for island reclamation site earthquake response analysis. © 2022, Science Press. All right reserved.