3171 Proceedings of the XVI ECSMGE Geotechnical Engineering for Infrastructure and Development ISBN 978-0-7277-6067-8 © The authors and ICE Publishing: All rights reserved, 2015 doi:10.1680/ecsmge.60678 Measuring travel time in bender/extender element tests Mesure du temps de propagation des ondes de compression et de cisaillement dans les milieu piézo-céramiques A.M. Hasan *1 and S.J. Wheeler 1 1 University of Glasgow, Glasgow, UK * Corresponding Author ABSTRACT Four different interpretation procedures (involving both time and frequency domains) have been examined for measuring travel times in bender/extender element tests, used for measurement of shear and compression wave velocities and hence elasti c shear mod- ulus and elastic constrained modulus, respectively. Tests were conducted on unsaturated samples of speswhite kaolin produced by an is o- tropic form of compaction, fitted with three pairs of bender/extender elements, two transmitting horizontally across the sample (with either vertical or horizontal polarisation of the shear waves) and one transmitting vertically. It was concluded that, for both shear and compression wave velocities, the procedure of determining travel time from a peak-to-first peak measurement in the time domain was the most reliable. This method, unlike the other three, provided a wave velocity that was almost frequency-independent (over an appropriate frequency range) and it also provided equal shear wave or compression wave velocities in different directions in these isotropic samples. RÉSUMÉ Quatre procédures d’interprétation (à la fois dans les domaines fréquentiel et temporel) ont été examinées pour mesurer les temps de propagation dans les éléments piézo-céramiques, utilises pour les mesures d’ondes de cisaillement et de compression, et donc les modules de cisaillement et élastique respectivement. Les mesures ont été effectuées sur des échantillons non saturés d’argile kaolinite de Speswhite, produits par une méthode de compaction isotropique, ajustée à trois paires d’élément piézo-céramiques - deux transmettant hor- izontalement à travers l’échantillon (avec une polarisation verticale ou horizontale des ondes de cisaillement) et un avec tr ansmission verti- cale. Il a été conclu, tant pour les ondes compressives que celles de cisaillements, que la méthode de mesure crête-à-crête était la plus fia- ble. Cette méthode, à la différence des trois autres, estime une vitesse d’onde quasiment indépendante de la fréquence (dans un domaine fréquentiel approprié) et prédit aussi pour ces échantillons isotropiques des vitesses d’ondes identiques dans toutes les directions. 1 INTRODUCTION Combined bender/extender elements provide meas- urements of shear wave velocity (V s ) and compres- sion wave velocity (V p ), which can be used to deter- mine small strain elastic shear modulus (G) and constrained modulus (M), respectively (Lings & Greening, 2001). To determine values of V s and V p , the travel time (t) must be determined for a shear wave or compres- sion wave to travel across a soil sample. Various dif- ferent techniques have been proposed for interpreta- tion of the bender element signal in order to determine t. These include interpretation methods in either the time-domain or the frequency domain. There is, however, considerable controversy within the literature about which of the various interpreta- tion techniques gives the most reliable and consistent values of travel time (see, for example, Yamashita et al. 2009). If bender/extender element measurements are to be used to provide meaningful values of elastic prop- erties, the measured travel time (t) must be sensibly independent of the chosen frequency of the transmit- ted wave, at least over an appropriate range of fre- quencies. For shear wave velocity measurements, this appropriate range of frequencies may be related to avoidance of the “near-field effect”, where distortion