Episodes 2020; 43(4): 991-1002
Published online December 1, 2020
Copyright © International Union of Geological Sciences.
by Seungbeom Choi1, Dae-sung Cheon1, Hoyoung Jeong2, Seokwon Jeon2*
1Geology Division, Korea Institute of Geoscience and Mineral Resources, 124 Gwahak-ro, Yuseong-gu, Daejeon, 34132, Korea
2Department of Energy Systems Engineering, Seoul National University, 1 Gwanka-ro, Gwanka-gu, Seoul, 08826, Korea
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Microfracturing in a solid generates elastic waves, being detected in a form of acoustic emission (AE). Using an array of AE sensors, the number and the location of AE sources can be successfully monitored. Rocks usually show anisotropic mechanical, thermal, and hydraulic characteristics. Especially, many sedimentary rocks present transversely isotropic features originated from complex geological processes. If the anisotropy were not properly considered, the accuracy and precision of the AE source locating would not be guaranteed. In this study, one of the source locating techniques, called partition approximation method, was investigated to check its applicability to a transversely isotropic medium. To validate the technique quantitatively, analytic and experimental investigations were conducted. Ideal and virtual two-dimensional specimens were used to check it and as a result, the technique was capable of locating both isotropic and transversely isotropic cases, showing maximum 6.9% of error when normalized by the size of specimen. Also, pencil lead break tests on artificial transversely isotropic specimen were performed. The averaged error was measured as 7.46 mm, which was smaller than the diameter of AE sensor used. In addition, Brazilian tension tests were conducted with AE monitoring as an application of the technique.