Ultrasonic evaluation of igneous and metamorphic rocks under compressive loading

Abstract

This research aims to assess deformability characteristics of extrusive volcanic and metamorphic rocks under compressive loading using ultrasonic wave propagation technique. An experimental methodology developed in house was used to measure applied load, resultant strain, P and S wave velocities along with maximum amplitudes simultaneously. Wave velocities were measured perpendicular to the compressional axis using pairs of receivers' lead-zirconate piezoceramic transducers (PZT) which are specifically designed for use in geological testing. PUNDIT instrument was used to generate low frequency ultrasonic pulses. According to the results, a non-linear relationship between velocities and stress level that rock specimens have undergone were found. Increase in velocities is closely related to closure of void spaces in the specimens. Rate of velocity increments was also found to be greatest at the early stress level. As a result, ultrasonic velocities can be used to detect high stress concentrations and to monitor stress level in the underground structures.