Evolution of the excavation damaged zone around a modelled disposal pit: case study at the Horonobe Underground Research Laboratory, Japan

PreviousNext No AccessProceedings of the 13th SEGJ International Symposium, Tokyo, Japan, 12–14 November 2018Evolution of the excavation damaged zone around a modelled disposal pit: case study at the Horonobe Underground Research Laboratory, JapanAuthors: Kazuhei AoyagiNobukatsu MiyaraEiichi IshiiMasashi NakayamaShun KimuraKazuhei AoyagiJapan Atomic Energy AgencySearch for more papers by this author, Nobukatsu MiyaraJapan Atomic Energy AgencySearch for more papers by this author, Eiichi IshiiJapan Atomic Energy AgencySearch for more papers by this author, Masashi NakayamaJapan Atomic Energy AgencySearch for more papers by this author, and Shun KimuraJapan Atomic Energy AgencySearch for more papers by this authorhttps://doi.org/10.1190/SEGJ2018-114.1 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract The construction of underground facilities induces fractures in the rock mass around the underground voids due to the resultant stress redistribution. This has particular implications for high-level radioactive waste (HLW) disposal projects, where fracture development creates an excavation damaged zone (EDZ) that increases the hydraulic conductivity of the surrounding rock mass and can provide a pathway for the migration of radionuclides from the storage facilities. It is therefore important to understand the long-term evolution of the EDZ and perform a comprehensive HLW disposal risk assessment. An in situ engineered barrier system experiment was conducted in the 350 m gallery at the Horonobe Underground Research Laboratory, Japan, to observe the near-field coupled thermo-hydro-mechanical-chemical (THMC) process in situ and validate coupled THMC models. Here we investigate the evolution of the EDZ around the gallery and model a test pit that was excavated below the floor of the gallery using a series of seismic tomography surveys. There was a significant decrease in the seismic velocity field around the test pit due to its excavation, which became slightly more pronounced over time after the excavation. These seismic results, coupled with hydraulic tests and pore pressure measurements around the pit, indicate that fracture development and the decrease in saturation around the test pit resulted in a decrease in the seismic velocity field after the excavation of the test pit. Furthermore, the increase in saturation around the test pit is a key reason for the increase in the seismic velocity field after the heater test. Keywords: seismic tomography, excavation damaged zone, fracture, saturation, hydraulic conductivityPermalink: https://doi.org/10.1190/SEGJ2018-114.1FiguresReferencesRelatedDetails Proceedings of the 13th SEGJ International Symposium, Tokyo, Japan, 12–14 November 2018ISSN (online):2159-6832Copyright: 2019 Pages: 588 publication data© 2018 Published in electronic format with permission by the Society of Exploration Geophysicists of JapanPublisher:Society of Exploration GeophysicistsSociety of Exploration Geophysicists of Japan HistoryPublished Online: 29 Apr 2019 CITATION INFORMATION Kazuhei Aoyagi, Nobukatsu Miyara, Eiichi Ishii, Masashi Nakayama, and Shun Kimura, (2019), "Evolution of the excavation damaged zone around a modelled disposal pit: case study at the Horonobe Underground Research Laboratory, Japan," SEG Global Meeting Abstracts : 443-447. https://doi.org/10.1190/SEGJ2018-114.1 Plain-Language Summary Keywordsseismic tomographyexcavation damaged zonefracturesaturationhydraulic conductivityPDF DownloadLoading ...