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The paper presents a study of the influence of grain-size distribution curve on the small strain shear modulus [G.sub.max] 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 [G.sub.max] is not influenced by variations in the mean grain-size [d.sub.50] in the investigated range, it significantly decreases with increasing coefficient of uniformity [C.sub.u]=[d.sub.60]/[d.sub.10] 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 [C.sub.u] 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 [K.sub.2,max] with [C.sub.u] 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 [G.sub.max]-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. DOI: 10.1061/(ASCE)GT.1943-5606.0000096 CE Database subject headings: Shear modulus; Sand; Coefficients; Grain size; Strain.

Cyclic stresses due to passing wheels impose an accumulation of permanent strains in layers of unbound granular materials (UGMs) of flexible pavements. The hollow cylinder triaxial test would be the most appropriate test to simulate the in situ stress conditions but it is difficult to perform on UGMs due to their large maximum grain size. The simpler axisymmetric cyclic triaxial test does not consider the shear stress components. It can be performed with a constant confining pressure (CCP) or a variable confining pressure (VCP). CCP and VCP tests are commonly assumed to deliver similar residual and resilient strains as long as the average stress is the same. Thus, the simpler CCP test is mostly used in pavement engineering. However, this assumption is based on limited test data in the literature and may not be on the safe side. The present paper documents a comparative study of CCP and VCP tests on UGM. The study is mainly dedicated to the permanent deformations. The results show that only for some special stress paths do both types of tests deliver similar permanent axial or volumetric strains. For some other stress paths the CCP tests may underestimate the permanent axial strain in comparison to the corresponding VCP test. DOI: 10.1061/(ASCE)TE.1943-5436.0000009 CE Database subject headings: Flexible pavements; Cyclic loads; Triaxial tests; Granular materials.

The modulus degradation curves, , and the damping ratio, , of 27 clean quartz sands with specially mixed grain size distribution curves were measured in approximately 280 resonant column tests. For each material, tests with various pressures and densities were performed. Based on the test data it is demonstrated that the shear modulus degradation is larger for higher values of the uniformity coefficient, , while it is rather independent of the mean grain size, . The observed dependence of curves is not adequately described by common empirical equations because these equations were developed based on tests on uniform granular materials. To consider the influence of the uniformity coefficient, the paper proposes correlations of the parameters of the common empirical equations with . Good agreement between the prediction of the extended empirical equations and the experimental data collected from the literature is demonstrated. Furthermore, the test data reveal that the curves of damping ratio, , and the threshold shear strain amplitude indicating the onset of residual deformation accumulation, , are rather independent of and . The threshold shear strain amplitude at the onset of modulus degradation, , slightly decreases with increasing values of and . [ABSTRACT FROM AUTHOR]

Abstract: The paper presents an experimental study on the influence of the grain size distribution curve on dynamic soil properties. More than 160 resonant column tests with additional P-wave measurements have been performed on 27 different grain size distribution curves of a quartz sand. While the small-strain shear modulus G max has been discussed by Wichtmann and Triantafyllidis the present paper focusses on P-wave velocity v P , on the small-strain constrained elastic modulus M max and on Poisson''s ratio . It is demonstrated that while v P and M max do not significantly depend on mean grain size d 50 in the investigated range, they decrease with increasing coefficient of uniformity C u =d 60/d 10 of the grain size distribution curve. Poisson''s ratio does also not depend on d 50 but increases with increasing C u . An empirical formula similar to Hardin''s equation has been developed for M max, considering the influence of the grain size distribution curve. It predicts quite well the experimental data. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]