Influence of Micro-Structure on Small-Strain Stiffness and Damping of Fine Grained Soil and Effects on Local Site Response

Various experimental studies have shown that soil micro-structure strongly influences the small strain stiffness and damping (G0, D0) of fine-grained soils, as well as their variation with shear strain γ. This dependency, in turn, is expected to influence the local site response. This paper firstly synthesizes the dependency of G0 and D0 on stress state through power relationships, expressed in terms of dimensionless parameters, obtained by fitting a large number of experimental data collected on normally consolidated natural clays. Thereafter, these parameters were correlated to soil micro-structure, by assuming the plasticity index Ip as a representative index property. Subsequently, in order to verify the effect of micro-structure on the local site response, a numerical sensitivity study was carried out on a reference subsoil by introducing in the 1D wave propagation model both non-linearity and hetherogeneity as correlated to variations of Ip