Energy Partitioning during Fracturing in Granite under Stress Relaxation

Abstract

Time-dependent deformation affects the fracturing in rocks and can reduce their failure strength. Such time-dependent deformations are important for surface and underground structures, which are typically designed for long operational time. The weakening of rock with time is directly related to the evolution of microcracks and in this study, we focused on the micromechanics of the fractures produced in crystalline rocks under time-dependent loading conditions. Stress relaxation experiments were conducted on double-flawed prismatic Barre granite specimen in the laboratory to investigate the fracturing processes in terms of the source mechanics and the source physics. Absolute calibration of the AE sensors was performed in the laboratory to identify individual sensor responses for a known source (ball drop). Source parameter analysis was undertaken using spectral fitting method obtained for the displacement spectra at each source location. Corner frequency and seismic moment were determined, ranging from 350 kHz to 650 kHz and 10-4 to 10-1, respectively. Finally partitioning of input and output energies during the fracture propagation under monotonic and multistage relaxation loading conditions was determined. Results suggest that the amount of radiated seismic energy during multistage relaxation experiments is almost the same as in the monotonic loading experiments, however, the number of cracks produced in case of multistage relaxation is higher than that of the monotonic loading experiments.The finding of this study can help us to better understand the fracturing processes in the various field applications dealing with time-dependent failure in rocks.