Real-time monitoring of heterogeneous fractures in rock: An experimental study

This study investigates the elastic anatomy of fractures in rock using full wavefield measurements. In this spirit, a 3-step experimental campaign is pursued in a laboratory setting, namely: (1) full-field 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 and posterior to fracturing, by a shear piezoelectric transducer at 10 and 30kHz. The (in-plane) velocity response of the rock is monitored via the 3D Scanning Laser Doppler Vibrometer over a rectangular region in the fracture neighborhood. Upon proper signal processing, (i) the maps of elastic modulus in the specimen (before and after fracturing) is computed via elastography, exposing the geometric and elastic properties of the process zone; (ii) the fracture geometry is reconstructed, and (iii) profiles of shear and normal specific stiffness at the fracture interface are identified.