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Aoyagi, Kazuhei; Tokiwa, Tetsuya*; Sato, Toshinori; Hayano, Akira
Proceedings of 2019 Rock Dynamics Summit in Okinawa (USB Flash Drive), p.682 - 687, 2019/05
In high-level radioactive disposal projects, it is important to investigate the extent of the excavation damaged zone (EDZ) for safety assessment because EDZ can provide a migration pathway for radionuclides from the facility. To investigate the quantitative differences between EDZs formed because of blasting and mechanical excavation, we studied the characteristics of fractures induced by excavation based on fracture mapping performed during shaft sinking (V- and E-Shafts). As a result, it was found that blasting excavation can lead to the formation of a large number of newly created fractures (EDZ fractures) compared with mechanical excavation. In addition, the seismic velocity (P-wave velocity) measured during blasting excavation (E-Shaft) was lower than that measured during mechanical excavation (V-Shaft). Furthermore, we found that the support pattern that reinforces forward rocks to be appropriate for limiting damage to the shaft wall.
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.
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.
Aoyagi, Kazuhei; Tokiwa, Tetsuya*; Fujita, Tomoo
Rock Mechanics and Rock Engineering; From the Past to the Future (EUROCK 2016), p.1023 - 1028, 2016/07
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