Measurement of low-strain material damping and wave velocity with bender elements in the frequency domain

This paper discusses the application of piezoceramic bender elements for measurement of damping ratio in the frequency domain in a triaxial cell under isotropic confinement. The emitter was excited with a constant voltage and varied frequency sine signal while the phase difference and amplitude in the receiver were measured. The resonant frequency and dynamic characteristics of cell components were analyzed to study the influence of possible additional modes when the modal analysis of a soil sample is performed. Damping ratio and shear wave velocity were determined in a sample of dry silica sand at different confinements from the first resonant mode of the sample. A relationship was found between measured travel time and resonant frequency that satisfies the solution for the general wave equation. The measured damping ratio compares very well with approximated empirical models. It is concluded that the methodology assumed in this work performs satisfactory when the dynamic response of the cell components is properly identified.