Influence of the Grain-Size Distribution Curve of Quartz Sand on the Small Strain Shear Modulus Gmax

The paper presents a study of the influence of grain-size distribution curve on the small strain shear modulus Gmax of quartz sand with subangular grain shape. The results of 163 resonant column tests on 25 different grain-size distribution curves are presented. It is demonstrated for a constant void ratio that while Gmax is not influenced by variations in the mean grain-size d50 in the investigated range, it significantly decreases with increasing coefficient of uniformity Cu=d60/d10 of the grain-size distribution curve. Well-known empirical formulas (e.g., Hardin’s equation with its commonly used constants) may strongly overestimate the stiffness of well-graded soils. Based on the RC test results, correlations of the constants of Hardin’s equation with Cu have been developed. The predictions using Hardin’s equation and these correlations are in good accordance with the test data. Correlations of the frequently used shear modulus coefficient K2,max with Cu and empirical equations formulated in terms of relative density, are also given in the paper. A comparison of the predictions by the proposed empirical formulas with Gmax-data from the literature and a micromechanical explanation of the experimental results are provided. Correction factors for an application of the laboratory data to in situ conditions are also discussed.