PIEZOELECTRIC RING ACTUATOR 

TECHNIQUE - P-RAT

With a unique interpretation method (e.g., Karray, 2008; Karray et al. 2015), the piezoelectric ring-actuator technique (P-RAT) was developed in the geotechnical laboratory at the Université de Sherbrooke (e.g., Gamal El-Dean 2007; Éthier 2009; Éthier et al. 2011, Karray et al. 2015) following a sustained work of several years of development under the supervision of Emeritus Professor Guy Lefebvre and Professor Mourad Karray for more objective measurement of shear wave velocity of soil, rock and cementitious materials. The P-RAT offers the ability to be incorporated in traditional geotechnical apparatus (e.g., oedometer, triaxial or simple shear cells), an advantage that facilitates its utilization in different geotechnical laboratories as a powerful tool in Vs measurement. The P-RAT essentially consists of two parts: an emitter and a receiver fastened in the top and bottom heads of the soil cell. Each part (the emitter or the receiver) is a piezoelectric inert ring covered at its outer and inner faces by a thin conductive layer. Both faces are welded to shielded wires that transfer voltage pulses with different durations and shapes. These voltage pulses cause the piezoelectric ring to vibrate in the radial direction. A porous stone is fitted inside the ring using a special epoxy to allow the propagation of shear wave when the coupled ring–stone system is in contact with the soil specimen. The wave reaches the receiver ring where its velocity is measured after signal processing.

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