Effect of mean grain size on shear modulus degradation and damping ratio curves of sands

Determination of shear modulus and damping ratio from small to large strains is essential to understand the non-linear stress–strain and damping behaviour of sand. The shear modulus and damping ratio with shear strain relationships of sand are dependent on a number of parameters: mean effective stress, void ratio, coefficient of uniformity, mean grain size and particle shape. The most common parameters investigated are mean effective stress and void ratio. This paper investigates the effect of the mean grain size on the normalised shear moduli and damping ratios of sands. Strain-dependent dynamic properties of sands are determined using bender element tests and cyclic triaxial tests at different mean effective stresses, void ratios and mean grain sizes. It was observed that normalised shear modulus and damping ratio increase as mean grain size decreases at a given strain amplitude. The effect of mean grain size was not considered in past empirical equations for the normalised shear modulus degradation and damping ratio curves. Hence, empirical equations were established for sand to incorporate the effect of mean grain size. The newly proposed empirical equations are shown to perform better than other empirical equations using data from the literature.