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Episodes 2020; 43(4): 991-1002

Published online December 1, 2020

https://doi.org/10.18814/epiiugs/2020/020063

Copyright © International Union of Geological Sciences.

Applicability of partition approximation source locating technique for a transversely isotropic medium

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

Correspondence to:*E-mail: sjeon@snu.ac.kr

Received: November 5, 2019; Revised: April 28, 2020; Accepted: April 28, 2020

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

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.