*Article* **Continuous Evaluation of Shear Wave Velocity from Bender Elements during Monotonic Triaxial Loading**

**Ahmed Khalil, Zahid Khan \*, Mousa Attom, Kazi Fattah, Tarig Ali and Maruf Mortula**

Department of Civil Engineering, American University of Sharjah, Sharjah P.O. Box 26666, United Arab Emirates **\*** Correspondence: zhkhan@aus.edu; Tel.: +971-(0)-6515-29262

**Abstract:** Few researchers have attempted to experimentally evaluate the low-strain shear wave velocity (*Vs*) of specimens undergoing large strain deformations. They report that the *Vs* is practically unaffected by the strains, and the reasons behind this behavior are not fully understood. This study presents the continuous measurement of low-strain *Vs* with bender elements (BE) during monotonic shearing of two sand specimens in a triaxial device. The results are analyzed using a micro-mechanical model based on contact theory. The results of this study confirm that the *Vs* values from BE measurements are unaffected by an increase in axial strains that are induced by a separate mechanism. The micro-mechanical model predictions of *Vs* agree well with the results of this study and with the results of previous studies. They show that the mean effective stress and increase in inter-particle stiffness controls the low-strain stiffness despite a global increase in strains during monotonic loading.

**Keywords:** shear wave velocity; bender elements; triaxial testing; micromechanics
