Small strain damping ratio of sands and silty sands subjected to flexural and torsional resonant column excitation

Damping ratio is a critical soil property used for the geophysical characterization of sediments and the study of the behavior of geo-materials against wave propagation. Two types of damping ratios are examined and quantified in this study conducting small-strain resonant column tests in torsional and flexural modes of vibration. During the course of this study, a variety of non-plastic soils from clean sands to silt-sand mixtures with variable index properties are examined and the laboratory specimens are subjected to isotropic stress conditions. Measurements and comparisons are conducted between flexural (D_fo) and torsional (D_so) damping. For clean sands, based on the data analysis, an empirical equation for (D_fo) is derived which is given as a function of (D_so) and the characteristics of the sands. Flexural damping ratios for all the tested materials are observed to have fairly equal or greater values and lower rate of variation with isotropic confining pressure compared to their torsional counterparts (D_so). Furthermore, the proportions of small-strain flexural and torsional damping ratios (D_fo/D_so) are obtained for all the tested sands and silty sands and plotted against the isotropic confining pressure. The results highlight the important role of particle shape, grain size distribution and silt content on the behavior of non-plastic geo-materials in terms of the ratio (D_fo/D_so).