Rock Masses Characterisation Using High Frequency Piezoelectric Systems

Seismic methods provide important in-situ measurements of the rock mass strength, which can be assessed through variations in seismic velocities. The frequency range in which seismic instruments operate dictates numerous key elements of a survey (e.g.detectability limits and resolution), and for engineering applications it is often advantageous to operate in kHz frequency range.

Piezoelectric sensors are rarely deployed in seismic surveys, but offer the potential for higher frequency content and more repeatable measurements compared with conventional instruments. This results in increased spatial resolution, and improvements in the stability of spectral measurements (e.g., spectral ratio methods).

To better understand some of the main characteristics of the piezoelectric system, we carry out a series of laboratory measurements on a range of different lithologies. Measurements were made to initially determine the frequency content on the system, followed by the response of the rock samples to these high frequency signal. We then present two crosshole datasets from ground excavations at Hinkley Point C, acquired using a piezoelectric seismic system and a conventional sparker system.