Dynamic Modulus and Damping Ratio Measurements from Free-Free Resonance and Fixed-Free Resonant Column Procedures: Fid-Bau Portal

Dynamic Modulus and Damping Ratio Measurements from Free-Free Resonance and Fixed-Free Resonant Column Procedures

Schaeffer, Kevin / Bearce, Richard / Wang, Judith

Abstract

Resonant column procedures may be used to quantify a soil’s shear modulus degradation and damping ratio curves along the small strain ( $∼ 10^{- 4} to ∼ 10^{- 1} %$ ) range. However, resonant column procedures often cannot provide measurements of very small strain ( $< ∼ 10^{- 4} %$ ) dynamic mechanical properties. The objective of this study is to determine if free-free resonance (FFR) procedures may be used to provide complementary very small strain, maximum dynamic moduli and minimum damping ratio to small strain shear moduli degradation and damping ratio curves from resonant column testing procedures. A plastic control specimen in six different free-free configurations was used to determine appropriate free-free boundary conditions for axial FFR procedures. Five cohesive soil specimens were then subjected to axial FFR and torsional fixed-free resonant column procedures to evaluate the consistency of the resulting strain-dependent modulus and damping measurements. It can be concluded that: (1) the specific free-free boundary conditions used in axial FFR testing do not significantly influence measured elastic or dissipative properties, and (2) axial FFR and torsional fixed-free resonant column procedures can be used to generate consistent and complementary shear modulus data but cannot be used to generate consistent and complementary damping ratios, based on the inherent issues involved in approximating nonlinear, microstructural sources of energy losses with macroscopic, equivalent linear models of dissipation.