Effect of Wave Attenuation on Shear Wave Velocity Determination Using Bender Element Tests.

Yanbin Gao,Hao Wang,Xiaojun Zheng,Wenkang Luo

doi:10.3390/s22031263

Yanbin Gao, Hao Wang + Show 2 more

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https://doi.org/10.3390/s22031263

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Abstract

Wave attenuation is a widespread physical phenomenon in most acoustic tests, but there is a scarcity of quantitative investigations into the influence of wave attenuation on the determination of shear wave travel time in bender element tests. To ascertain this attenuation effect, a series of bender element tests were conducted on clay samples with different lengths under unconfined conditions. The experimental results suggest that the real first peak of the received signal attenuates gradually with the increase of the sample length and even becomes undistinguished when the sample length exceeds a limit. This phenomenon results in misinterpretation of the wave travel time using the time domain method. In this study, the shear wave travel time is misinterpreted when wave travel distance over approximately 80 mm, leading to underestimation of the VS by 17% for the peak-to-peak approach and 10% for the arrival-to-arrival method. Therefore, besides the near field effect and boundary reflection, the wave attenuation effect turned out to be an important factor influencing the determination of VS using the time domain method. Accordingly, it is advisable to predetermine the limit test distance for a specific testing system under conditions, particularly for long distance testing.

Highlights

The shear wave velocity (V S ) is a fundamental soil parameter, which can be used for liquefaction evaluation [1,2], sample quality assessment [3], and small-strain shear stiffness determination [4]
Wave attenuation in bender element testing has been observed here to serve as a contributing factor influencing received waveforms and shear wave velocity determination by the time domain method for long samples
The wave attenuation may make the over-estimation of the shear wave (S-wave) travel time and under-estimation of the V S

Summary

Introduction

The shear wave velocity (V S ) is a fundamental soil parameter, which can be used for liquefaction evaluation [1,2], sample quality assessment [3], and small-strain shear stiffness determination [4]. Since the bender element method was first introduced for soil testing by Shirley and Hampton [5] and Shirley [6], it has been widely installed in geotechnical testing devices to obtain V S of geotechnical materials (such as clay and sand), including oedometers, direct shear apparatuses, triaxial apparatuses, resonant columns, and even applied in scaled physical model tests. Bender element test commonly adopts transmitter–receiver measurement mode (not the resonant mode) based on the direct-arrive wave principle. The determination of V S can be expressed as published maps and institutional affil- Vs = iations.

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