Characterization of the small-strain dynamic behaviour of silty sands; contribution of silica non-plastic fines content

Dynamic properties of soils at very small strains are of particular interest for geotechnical engineers for the characterization of the behaviour of earth structures subjected to a variety of static and dynamic stress states. This study reports on the small-strain dynamic properties of silty sand with particular emphasis on the effect of non-plastic fines content on the small-strain shear modulus (Gmax) and material damping (Ds,min). Several clean sands with a wide range of grain size distribution and particle shape are mixed with different percentages of a silica non-plastic silt. The laboratory created samples are subjected to torsional resonant column tests with small-strain shear moduli and damping ratios measured along an isotropic stress path. It is shown that at low percentages of fines content, there is a significant difference between the dynamic properties of the various samples due to the different characteristics of the sand portion of the mixtures. However this variance diminishes as the fines content increases and the soil behaviour becomes mainly silt-dominant, rendering no significant influence of different sand properties on the small-strain shear modulus and damping ratio. Using the experimental results, new expressions for the prediction of small-strain shear modulus and small-strain damping ratio of non-plastic silty sands are developed accounting for the percentage of silt and the characteristics of the sand portion.