Parametric analysis of laboratory Acoustic Emission (AE) during rock deformation laboratory experiments on Alzo granite has revealed periodic trends and precursory behavior of the rupture source, as crack damage nucleates, it grows and coalesces into a fault zone (King et al., JGR, 2021). Numerical simulations were carried out to understand the relationships between fracture nucleation, growth and propagation, and AE source mechanisms in Alzo granite experiments, where 4x10cm cylindrical samples were triaxially deformed at confining pressures of 5-40 MPa, recorded AE signals then post-processed to derive attributes and parameters (King et al., 2021).
The numerical simulation experiments were conducted with the Particle Flow Code (PFC) by reproducing the laboratory experiments, including sample dimensions, porosity, density, Young's modulus, confining pressure, and strain rate. The numerical simulation results showed a high degree of reproducibility of the laboratory experiments, revealing the mechanism sources of fracturing onset and propagation from a microscopic perspective.
Currently, the stress-strain curve of the numerical model matches the laboratory experiments with a fidelity of over 98% under the four different confining pressures. Additionally, on the basis of energy conservation and particle fracture mechanism assumptions, we have isolated the source mechanisms preceding and accompanying rock failure. Based on the fundamental fracture generation mechanism in the PFC model, we use the focal mechanisms method to identify three distinct fracture modes in numerical simulations, namely Shear-c, Shear-t, and Tension. correspond the C-Type, S-Type, T-Type in the laboratory experiments, T-Type events were found to dominate in dynamic failure, while C-Type events accurately represented the precursor stage before reaching the critical failure threshold, in good agreement with the same parameters obtained by focal mechanisms in King et al., 2021. As the PFC can simulate AE signals based on the energy released at the deformation and rupture of grain bonds, namely "epbstrain" and "epbfailure", we propose the AE Amplitude Classification Method (AEACM) for identifying and classifying the amplitudes of AE events. Notably, we discovered that high-amplitude AE events increased proportionally to the total event rate increase, as the confining pressure increased.
Currently, our investigations focus on understanding the relationship between the AE burst area and energy dissipation. Higher energy dissipation occurs in areas of high-burst AE. However, PFC can only monitor the energy of single particle fracture. Consequently, we are developing new methods to classify amplitudes over time and their occurrence throughout crack propagation.
