Measuring Shear Wave Velocity Using Bender Elements

Abstract

The use of bender element to measure shear wave velocity is popular due to its simplicity. However, there are still some uncertainties in the interpretation of the bender element test. In this paper, the use of bender elements in the determination of shear wave velocities of dry, unsaturated, and saturated soil specimens is examined with respect to the characteristics of the bender elements, waveform, magnitude, and frequency of the applied voltage to the transmitter bender element and method of travel time determination. The interpretation of the bender element test can be improved if two performance criteria are adopted: (1) a signal-to-noise ratio of at least 4 dB for the receiver signal, and (2) a wave path length to wavelength ratio of at least 3.33. Procedures to estimate the strain level associated with the shear wave velocity measurement using bender element are also described.

Dynamic Characterization of Cohesive Material Based on Wave Velocity Measurements

“…For the start-to-start method, the noise level is very significant. Leong et al [40] verified the criteria for the improvement of the interpretation of the BE test, among which there is the signal-to-noise ratio (SNR) criterion. According to their research, the SNR should be of at least 4 dB for the receiver signal.…”

Bender elements in stiff cemented clay: shear wave velocity (Vs) correction by applying wavelength considerations

“…Cruse and Rizzo (1968) and Sanchez-Salinero et al (1986) analytically predicted the presence of near field components in shear waves traveling through a medium. Experimental observations further confirmed the presence of near field effects (Brignoli et al 1996;Leong et al 2005). Arroyo et al (2003) described the near field component in the arriving shear waves as a "distorted and transposed replica of the input signal".…”

“…Depending on the cement content, water content and curing time, a range of input frequencies are utilized to consider the varying stiffness values of all mix ratios in this study. Consequently, it is demonstrated that the study successfully establishes the reliability of the proposed function in correcting V s values obtained at lower L tt /λ ratios to more accurate V s values that correspond to standardized L tt /λ ratios of 2, 3.33 and 4 (Leong et al 2005;Sanchez-Salinero et al 1986).…”

“…The upper limit was given to prevent signal attenuation due to damping. Leong et al (2005) prescribed using a ratio of 3.33 or greater as a criterion. However, strictly adhering to these limits can become tricky by using bender elements for stiffer materials due to the requirement of high input frequencies for such samples.…”

“…Abiding by a slenderness ratio of 2 as well as other dimensional requirements suggested by (Sawangsuriya 2012) for addressing the influence of wave reflections can pose practical challenges. Longer samples also may result in lower signal to noise ratio which can cause weaker output signals (Leong et al 2005). These challenges have led to various other techniques being suggested in the time domain for replacing the first arrival method.…”