Active ultrasonic imaging and interfacial characterization of stationary and evolving fractures in rock

This investigation aims to elucidate the elastic anatomy of fractures in laboratory rock specimens, using full-field ultrasonic measurements. To this end, a three-step testing paradigm is adopted, which includes: (1) ultrasonic testing of the intact rock, (2) fracturing, and (3) ultrasonic interrogation of the fractured rock. Experiments are performed on a slab-like prismatic specimen of charcoal granite. The sample is illuminated under the plane stress condition, prior to and post-fracturing, by a shear piezoelectric transducer excited at 10 and 30 kHz. The generated (in-plane) wave motion in the specimen is then monitored over a rectangular region covering the fracture by a 3D scanning laser doppler vibrometer. After suitable signal processing, the full-field ultrasonic waveforms are used to: (i) reconstruct the curvilinear fracture geometry, (ii) compute the maps of (heterogeneous) elastic modulus in the specimen, using the data interpretation technique known as elastography, and (iii) recover the profiles of (heterogeneous) shear and normal specific stiffness along the fracture.