Shear modulus and damping relationships for dynamic analysis of compacted backfill soils

Dynamic analysis of structures often considers the effects of soil–structure interaction which requires estimation of the shear modulus and damping ratio of the soil. While the in situ properties can be measured, the properties of the backfill soils that surround substructures are rarely available at the time of design and in many cases are never measured. This study provides a practical means of estimating properties for compacted coarse-grained soils based on relative density. The results of more than 400 tests gathered from the literature were used to develop correlations between the small strain shear modulus, G_max and relative density for compacted coarse-grained soils, which can be used when the mechanical properties are not available. The proposed relationships better distinguish between the behavior of sand and gravel compared to existing correlations. Best-fit hyperbolic curves are also presented for the variation of normalized shear modulus and damping ratio with shear strain for compacted coarse-grained soils to represent the nonlinear behavior of the backfill in the dynamic analysis.