A Study of the evaluation of the excavation damaged zone in the Horonobe Underground Research Laboratory, 1; Investigation in the 140 m gallery (Joint research)

Sugita, Yutaka; Aoyagi, Kazuhei; Kubota, Kenji*; Nakata, Eiji*; Oyama, Takahiro*

JAEA-Research 2018-002, 72 Pages, 2018/06

JAEA-Research-2018-002.pdf:6.16MB

In a excavation of shafts and galleries in the deep underground for disposing radioactive waste, an excavation damaged zone (EDZ) is developed around the galleries and shafts owing to the stress redistribution. Since the characteristic changes of the rock mass in the EDZ affects the radionuclides migration behavior, it is important to understand the long-term behavior of the EDZ. Thus, we performed the in situ experiment to investigate the long-term behavior of EDZ as part of the collaborative research between Japan Atomic Energy Agency and Central Research Institute of Electric Power Industry in the 140m gallery in the Horonobe Underground Research Laboratory. In this research, we investigated the extent, mechanism of the change of hydro-mechanical characteristic, and long-term behavior of the EDZ on the basis of the comprehensive estimation of the results of the observation of the drift wall and the various investigations using boreholes such as geological investigation, the seismic and resistivity tomography, hydraulic test, water content monitoring, borehole loading test, convergence measurement, and so on. In addition, we clarified applicability and future tasks of the testing method used in this research for the investigation of the long-term behavior of the EDZ.

A Study of the evaluation of the excavation damaged zone in the Horonobe Underground Research Laboratory, 2; Investigation in the 250 m gallery (Joint research)

Aoyagi, Kazuhei; Kubota, Kenji*; Nakata, Eiji*; Suenaga, Hiroshi*; Nohara, Shintaro*

JAEA-Research 2017-004, 91 Pages, 2017/06

JAEA-Research-2017-004.pdf:6.07MB

In this study, we performed seismic tomography, seismic refraction survey, resistivity tomography, and hydraulic tests to investigate the hydro-mechanical property of the excavation damaged zone (EDZ) in the 250 m gallery of the Horonobe Underground Research Laboratory. As a result of seismic tomography, seismic velocity is significantly decreased within 1 m from the gallery wall. The decrease of seismic velocity is related to the density of fracture induced around the gallery wall as a result of the gallery excavation. Thus the extent of the fractures induced by gallery excavation, i.e., EDZ fractures is clarified to be within 1.0 m from the gallery wall. The enhanced hydraulic conductivity was detected within 0.5 to 1.0 m from the gallery wall on the basis of the result of hydraulic tests. This is almost consistent with the extent of the region that seismic velocity is significantly decreased. Therefore, it is estimated that EDZ fractures induced around the gallery leads to the increase of hydraulic conductivity. In addition, the desaturation zone around the gallery is not induced as a result of resistivity tomography. From these results, the hydro-mechanical property of the EDZ is clarified in detail. Also, the in situ tests and evaluation method applied in this study are appropriate to investigate the EDZ in detail.

Hydrogeomechanical investigation of an excavation damaged zone in the Horonobe Underground Research Laboratory

Aoyagi, Kazuhei; Tsusaka, Kimikazu*; Nohara, Shintaro*; Kubota, Kenji*; Tokiwa, Tetsuya*; Kondo, Keiji*; Inagaki, Daisuke*

Proceedings of 8th Asian Rock Mechanics Symposium (ARMS-8) (USB Flash Drive), 8 Pages, 2014/10

Monitoring of the excavation damaged zone (EDZ) by geophysical methods during the test tunnel excavation at a depth of 140 m and 250 m

Kubota, Kenji*; Kondo, Keiji; Sakakibara, Junichi*

Shadan Hojin Butsuri Tansa Gakkai Dai-128-Kai (Heisei-25-Nendo Shuki) Gakujutsu Koenkai Koen Rombunshu, p.62 - 65, 2013/06

To evaluate the excavated damaged zone (EDZ) is one of the important factors to conduct high level radioactive waste disposal. We have conducted resistivity and acoustic tomography to evaluate EDZ during the excavation of the test tunnel at a depth of 140 m and 250 m. As a result, a few meters extent of high resistivity and low P-wave velocity zone were detected at a depth of 140 m. This suggests that EDZ by excavation of horizontal tunnel was estimated by resistivity and acoustic tomography. On the other hand, high resistivity zone were not detected at a depth of 250 m.

Time-lapse measurement of resistivity and acoustic tomography during the excavation of the test tunnel at a depth of 140 m

Kubota, Kenji*; Suzuki, Koichi*; Sugita, Yutaka; Sakakibara, Junichi*

no journal, , 

no abstracts in English

Investigation of the excavation disturbed zone due to the excavation of galleries; Study in the Horonobe Underground Research Laboratory

Kubota, Kenji*; Morifuji, Yohei*; Aoyagi, Kazuhei; Sugita, Yutaka

no journal, , 

We performed in-situ experiments such as seismic and electrical resistivity tomography, geological survey and so on before, during, and 11 years after excavation of galleries at 140 and 250 m depth in an area of soft sedimentary rock in the Horonobe Underground Research Laboratory, Hokkaido, Japan. The results demonstrate that the extent of fractures and unsaturated zone induced by the gallery excavation were clarified. The extent of fractures related with EDZ was limited in about 0.45 m from the gallery wall in the 140 m gallery and to about 1 m from the gallery wall in the 250 m gallery. The extent of the unsaturated zone related with EdZ was about 1 m in the 140 m gallery, but it was not appeared in the 250 m gallery. Such changes induced by the gallery excavation occurred within one year after gallery excavation. On the other hand, the extension of the developed fractures and unsaturated zone was hardly clarified in about 11 years after gallery excavation.

Investigation of the development of excavation damaged zone and unsaturated zone due to the gallery excavation; Study in the Horonobe Underground Research Laboratory (2)

Kubota, Kenji*; Morifuji, Yohei*; Oyama, Takahiro*; Matsui, Hiroya

no journal, , 

This report summarize the results of resistivity tomography around the drifts during 10 years after the excavation in Horonobe URL and investigation of core samples within the tomography region.