Study on the Temporal-Spatial Evolution Characteristics of Micro-Cracks During Fault Slip Based on Acoustic Emission Monitoring

Stress redistribution can disturb existing faults, leading to fault shear slip. Investigating the abnormal phenomena during the fault transition from steady to instability stages is crucial for reducing the risk of dynamic disasters caused by fault slip instability. This study, based on the fault slip disaster encountered during tunnel excavation at the Jinping II Hydropower Station, involves experimental and numerical simulation research on progressive fault slip induced by static stress loading, using acoustic emission (AE) monitoring technology. The research analyzes the temporal and spatial evolution characteristics of AE at various stages of the fault slip process through experiments. Numerical simulations are also conducted to supplement and verify these findings, illustrating the influence of the dip angle and confining stress on fault slip. The findings reveal that the temporal and spatial evolution characteristics of AE events can characterize the stage of fault slip. During the linear steady stage, AE events are fewer in number and more randomly distributed spatially. In contrast, during the nonlinear steady state, AE activity significantly increases and primarily disperses across the fault plane, forming isolated weakening points. In the meta-instability stage, numerous AE events are concentrated on the fault plane, expanding to form a macroscopic fracture plane. These AE events predominantly extend vertically on both sides of the fault, creating a shear fracture zone of a certain thickness. In addition, this research establishes temporal sequence indicators, peak stress sigma peak, spatial evolution indicators, the number of fragments n, and the damage factor m to analyze the temporal-spatial evolution characteristics of micro-cracks during the fault slip process. Confining stress restrains the fault slip process, while the dip angle influences the fault slip opening and closing. Increasing normal restraint, adopting grouting supports, and controlling top pressure are recommended to mitigate disaster risks. This research provides significant insights for identifying different stages of fault slip and offers vital clues for reducing the risk of geological disasters caused by fault slip.