68th Canadian Geotechnical Conference and 7th Canadian Permafrost Conference

NOVEL EVALUATION OF BENDER RESPONSE IN SAND SPECIMENS USING A LASER VIBROMETER

Session: Laboratory Testing III / Essais en laboratoire III

Muhammad Irfan, University of Waterloo (Canada)
Giovanni Cascante, university of waterloo (Canada)
Dipanjan Basu, university of waterloo (Canada)
zahid khan, american university of sharjah (United Arab Emirates)

Bender elements (BE) are used to measure the shear-wave velocity of soils in many geotechnical laboratories worldwide. Despite its popularity, the method remains without a standard procedure, mainly because of the difficulties in controlling the actual behavior of BE inside the soil specimen. Previous studies have monitored and/or simulated the behavior of BE, finding evidence that the actual transmitter movement is not equal in shape and frequency content of the electrical signal used as excitation. However, this is not supported by any direct measurements of BE transmitter vibrations. In this study, a transparent soil is used in conjunction with a laser vibrometer to obtain actual BE transmitter movements in the transparent soil. Measurements of transmitter BE are obtained in air and in transparent soil under five different stresses. Results show that the BE response in air with a sine pulse excitation resembles the response of a single-degree-of-freedom (SFOD) system. However, the BE response in soil is significantly different with the same excitation. Moreover, the BE response in the transparent soil shows an unexpected variation in amplitude with increase in stress; whereas, there is an increase in frequency of vibration that is consistent with the increase in the medium stiffness.