Fracture compliance measurements in synthetic fractured media

Abstract

Ultrasonic velocities were measured on a stack of synthetic material (plexiglass plates), at low (90/120 kHz, long wavelength range: 12-23 mm) and high (431/480 kHz, short wavelength range: 1-6 mm) frequencies. The plexiglass plates were pressed together with uniaxial normal stress. The ultrasonic measurements were repeated under different uniaxial stresses with and without circular rubber inclusions between the plates. Ultrasonic velocity measurements in vertical and horizontal directions were used to calculate normal and tangential fracture compliances. C13 in all cases was computed using linear slip theory. For both experiments, fracture compliances (normal and tangential) decrease with increasing stress and frequency. In all cases, the tangential compliance was greater than the normal compliance. Stress affects the tangential compliance more than the normal compliance. For variations of normal to tangential compliance ratios with stress, two different general trends can be observed for cases with and without inclusions. For experiments without inclusions, the normal to tangential compliance ratios show an increasing trend with increasing normal stress. For experiments with inclusions, these ratios show a decreasing trend especially at higher frequency range.