[SSS15-P09] Frequency characteristics of acoustic emission in granite during triaxial compression tests
Keywords:acoustic emission, frequency, triaxial compression test
We conduct a triaxial compression test on granite at confining pressure of 22.5 MPa and strain rate of 10-5 1/s under dry condition using the loading system at GSJ/AIST (Lei et al., 2011). Cylindrical intermediate-grained Oshima granite and coarse-grained Inada granite (50 mm in diameter and 125 mm in length) which are thermally damaged at 550 ℃ are used as samples. We measure AEs with twenty-eight piezoelectric transducers (PZT) and strains with six strain gauges.
A preliminary result shows that a sample deforms elastically until at 384 MPa. After the peak stress of 438 MPa, post-yield behavior of the sample indicates brittle deformation with drastic stress drop. AE activity was initiated at around 80 % of the peak stress, and increased rapidly after reaching the peak stress. Initiation and growth of cracks inferred from AE events is consistent with the damaging process proposed by Lei (2006). Frequency analysis based on the fast Fourier transform shows that frequency of AE signals released during deformation are in the range of 100-300 kHz. Previous study reported that low-frequency events were dominant as rock approached failure under compression (Ohnaka and Mogi, 1982). However, no clear variation in frequency band was found from the results of this study. This is because AEs were not recorded in a range sufficient to understand the whole trend, and it is necessary to record AE signals from the initial stage of deformation, such as using transducers with different frequency band.