Shear Modulus and Damping Relationships for Dynamic Analysis of Structures with Backfill Effect

Abstract

Dynamic analysis of structures using numerical methods should consider the effects of soil-structure interaction, including the shear modulus and damping ratio of the soil.  Structures that extend below grade will interact with both the natural soil and the compacted backfill surrounding the substructure.  While the in situ properties can be measured, the properties of the backfill are rarely available at the time of design.  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 on reconstituted or compacted coarse-grained soils have been collected from the literature for this purpose.  In particular, the data were used to develop correlations between the small strain shear modulus, Gmax and relative density for both sand and gravel.  Most of the sand data plots below existing correlations from the literature, while most of the gravel data has higher values of Gmax.  Thus the proposed correlations are better at distinguishing between the behavior of sand and gravel.  Based on a subset of the collected data, updated curves are also presented for the variation of normalized shear modulus and damping ratio with shear strain.