Abstract: The subgrade backfill material characteristics of a tourist highway surrounding the Hainan Island is presented as an engineering case history. The dynamic characteristics of a narrowly graded fine sand as the subgrade backfill material were studied in the paper. The gradation curve of the narrowly graded fine sand is obtained throughout the laboratory sieve analyses, with curvature coefficient of 1.0 and the non-uniformity coefficient of 2.0. The GDSRCA resonant column test system is used for the experimental study. Based on the Hardin Drnevich model, the characteristics of the dynamic shear modulus and the damping ratio variation with the dry density and the confining pressure under the same water content are analyzed. The dynamic shear modulus of the sand sample decreases with the increase of the dynamic shear strain and increases with the increase of the consolidation confining pressure and the dry density. When the dry density is the same, the dynamic shear modulus ratio of the sample increases with the increase of the confining pressure, and the damping ratio decreases. At the same confining pressure, the dynamic shear modulus ratio of the sample increases with the increase of the dry density, and the damping ratio increases.  ratio is reduced.  The dynamic shear modulus ratio and the damping ratio have a certain discreteness, and the discrete degree of damping ratio is higher than that of the dynamic shear modulus ratio.

Key words: Resonant Column Test System, Dynamic Shear Modulus, Damping Ratio