High strain damping for sands from load-controlled cyclic tests: Correlation between stored strain energy and pore water pressure

Abstract

Undrained stress-controlled cyclic triaxial and direct simple shear test data on five different clean sands was analyzed in terms of dissipated and stored strain energy. A new method was developed to calculate damping ratio from undrained stress-controlled tests and its plausibility was examined with the help of pore water pressure data. Results from different methods in the literature to calculate damping ratio were also evaluated. The data analysis shows that the damping ratio results calculated with the new method were in some agreement with the damping ratio values for sands summarized by Seed & Idriss (1970) [1] for shear strains up to 0.4%. For shear strains larger than 0.4%, the new method provides more accurate estimates of damping ratio that are also conceptually more reasonable than those obtained with linear equivalent approximations. For strains in excess of 1%, damping ratio trends with strain obtained with the new method are clearly superior, although reliable experimental data is limited. In general, equivalent linear calculation of damping ratio can lead to an overestimation of damping for shear strains smaller than 1% and an underestimation of damping for the shear strains larger than 1%.