Novel Methods for the Computation of Small-Strain Damping Ratios of Soils from Cyclic Torsional Shear and Free-Vibration Decay Testing

Abstract

This paper illustrates two novel methods for computing the small-strain hysteretic material damping ratio, λmin, of soils from the cyclic torsional shear (TS) and computing the small-strain viscous material damping ratio, Dmin, from the free-vibration decay (FVD) testing. Both λmin and Dmin are challenging to measure, due to the significant level of ambient noise at small strains (<10−4%). A two-step method is proposed combining the Fourier Transform and a phase-based data fitting method for torsional shear testing, and this method can effectively eliminate the ambient noise at small strains. A Hilbert Transform-based method is proposed for the free-vibration decay testing in order to achieve a more accurate measurement of the viscous material damping ratio, D, at different strain levels, especially at small strains. The improved λmin and Dmin at small strains are compared to data available in the literature. The two novel methods are shown to be accurate in computing the small-strain damping ratios.