Estimation of the zone of excavation disturbance around tunnels, using resistivity and acoustic tomography

Suzuki Koichi; Nakata Eiji; Minami Masayuki; Hibino Etsuhisa; Tani Tomonori; Sakakibara Jyunichi; Yamada Naouki

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자료유형: 학술저널

저자정보: Suzuki Koichi (Central Research Institute of Electric Power Industry) Nakata Eiji (Central Research Institute of Electric Power Industry) Minami Masayuki (Tokyo Electric Power Company) Hibino Etsuhisa (Tokyo Electric Power Company) Tani Tomonori (Tokyo Electric Power Service Co. Ltd) Sakakibara Jyunichi (JFE Civil Engineering & Construction Corp) Yamada Naouki (Dia Consultants Co. Ltd.)

저널정보: 한국지구물리.물리탐사학회 지구물리와 물리탐사 지구물리와 물리탐사 제7권 제1호

발행연도: 2004.1

수록면: 62 - 69 (8page)

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The objective of this study is to estimate the distribution of a zone disturbed by excavation (EDZ) around tunnels that have been excavated at about 500 m depth in pre-Tertiary hard sedimentary rock. One of the most important tasks is to evaluate changes in the dynamic stability and permeability of the rock around the tunnels, by investigating the properties of the rock after the excavation. We performed resistivity and acoustic tomography using two boreholes, 5 m in length, drilled horizontally from the wall of a tunnel in pre-Tertiary hard conglomerate. By these methods, we detected a low-resistivity and low-velocity zone 1 m in thickness around the wall of the tunnel. The resulting profiles were verified by permeability and evaporation tests performed at the same boreholes. This anomalous zone matched a high-permeability zone caused by open fractures. Next, we performed resistivity monitoring along annular survey lines in a tunnel excavated in pre-Tertiary hard shale by a tunnel-boring machine (TBM). We detected anomalous zones in 2D resistivity profiles surrounding the tunnel. A low-resistivity zone 1 m in thickness was detected around the tunnel when one year had passed after the excavation. However, two years later, the resistivity around the tunnel had increased in a portion, about 30 cm in thickness, of this zone. To investigate this change, we studied the relationship between groundwater flow from the surroundings and evaporation from the wall around the tunnel. These features were verified by the relationship between the resistivity and porosity of rocks obtained by laboratory tests on core samples. Furthermore, the profiles matched well with highly permeable zones detected by permeability and evaporation tests at a horizontal borehole drilled near the survey line. We conclude that the anomalous zones in these profiles indicate the EDZ around the tunnel.

#resistivity tomography #acoustic tomography #excavation disturbance #tunnel

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