Experimental investigation of dynamic shear modulus of saturated marine coral sand

Shear modulus is an essential parameter for deformation prediction and site response analysis of geological problems. This paper considers the dynamic shear modulus degradation of saturated marine coral sand containing fine particles from a reef in the Nansha Islands. Resonant-column tests were carried out on specimens of the saturated coral sand with varying non-plastic fines content (FC) and relative density (Dr) subjected to initial effective confining pressure (σ′m). The test results show that the stress exponent n—which reflects the rate of increase of the maximum dynamic shear modulus (Gmax) with increasing σ′m—is a soil-specific constant. A significant finding is that the equivalent skeleton void ratio e*sk has a unique power relationship with the normalised maximum dynamic shear modulus [Gmax/(σ′m/Pa)n]. An improved Hardin model based on binary packing theory is proposed to evaluate Gmax of the coral sand, and its applicability is verified using experimental data for three different sands from the literature. For a given shear strain, dynamic shear modulus G decreases with increasing FC and increases with increasing Dr and σ′m. The curves of the maximum dynamic shear modulus rate (G/Gmax) tend to fall with increasing FC, while Dr and σ′m have little influence on G/Gmax. The fitting parameters A and B of the Davidenkov model are insensitive to σ′m, Dr, and FC and are fixed at 1.08 and 0.42, respectively, for the saturated coral sand. Furthermore, the reference shear strain γ0 in the Davidenkov model—corresponding to the shear strain at G/Gmax = 0.5—can be evaluated uniformly by e*sk regardless of σ′m, Dr, and FC. A unified form of shear-strain-dependent G prediction method is established and provides a significant advantage in evaluating G for marine coral sand in practice.