Experimental and Numerical Observations of the Frequency-Domain Method in Bender-Element Testing

Abstract

In bender-element (BE) testing, shear-wave velocities are measured using two main methods: time-domain analysis of vibration data from pulse excitation and frequency-domain analysis of vibration from sine-sweep excitation. The frequency-domain analysis can be performed automatically. However, its results show high variability because they are affected by different variables such as the frequency content of the excitation, the resonant frequency of the BE system, and the resolution of the frequency-domain analysis. The reliability of the frequency-domain method is studied in this paper using simplified mathematical models and experimental results from BEs, miniature accelerometers, and resonant-column (RC) tests. The mathematical models are used to understand the effects of different variables in the frequency-domain method. Both laboratory and numerical results show that amplification peaks in the transfer function of the BE system can significantly affect the estimation of the shear-wave velocity. A modified frequency-domain analysis is proposed to enhance the reliability of the method using a high-frequency narrowband excitation outside the resonant peaks of the BE system. Results from the modified frequency-domain analysis tests show less than 10% error in the measurement of the shear-wave velocity with respect to the RC results.