关键词: 岩石破坏实验, 声发射, 断层成核, 亚临界破裂扩展, b值

Abstract: Based on the experimental results of two similar rocks having high/very low microcrack density under two extremely different loading conditions: fast constant stress rate (～6 MPa/m) loading and creep (at ～95% of the fracture strength) loading,the role of pre-existing microcracks and loading condition on the fracturing properties of granitic rocks was examined. The detailed spatio temporal distribution of acoustic emission (AE) events in these samples were monitored by the use of a high-speed multi-channel waveform recording system,which can record AE waveforms from 32 sensors mounted on the surface of tested sample without a major loss of events even for an event rate on the order of several thousand events per second. Event rate,b-value in magnitude-frequency relation,and hypocenter distribution of AE events characterize three typical long-term stages of microcracking activity during the fracturing process: primary,secondary and nucleation. Precursory anomalies on cracking activity such as event rate and b-value in the nucleation stage were observed. In general,a higher pre existing microcrack density or a lower loading stress-rate results in a longer nucleation stage,and therefore,increases the predictability of catastrophic failure event. Further,the physics of these stages is analyzed using the subcritical crack growth model for crack population of fractal size distribution based on the stress-aided corrosion theory.

Key words: rock fracture experiment, acoustic emission, fault nucleation, subcritical crack growth, b-value