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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.
Sato, Toshinori; Aoyagi, Kazuhei; Miyara, Nobukatsu; Aydan, 
mer*; Tomiyama, Jun*; Morita, Tatsuri*
Proceedings of 2019 Rock Dynamics Summit in Okinawa (USB Flash Drive), p.640 - 645, 2019/05
An earthquake with a moment magnitude of 4 occurred in June 20, 2018, which is also named as the 2018 June 20 Soya Region earth-quake. The strong motions induced by this earthquake were recorded by the accelerometers installed in the Horonobe URL as well as the Kik-Net and K-Net strong motions networks operated by the National Research Institute for Earth Science and Disaster Prevention of Japan. The authors explain the results of the analyses carried out on the ground amplification and frequency characteristics of the acceleration records at the Horonobe URL and those of the Kik-net strong motion station and the structural effect of the URL on the ground amplification and frequency characteristics. Furthermore, the authors discuss the implications of the results obtained from this study in practice and the safety of the nuclear waste disposal at depth.
Kubota, Kenji*; Aoyagi, Kazuhei; Sugita, Yutaka
Proceedings of 2019 Rock Dynamics Summit in Okinawa (USB Flash Drive), p.729 - 733, 2019/05
During the excavation of shafts and galleries in the deep subsurface for disposing of high-level radioactive waste, an excavation disturbed zone (EdZ) or excavation damaged zone (EDZ) is developed around the shafts and galleries. Such zones could influence the transfer behavior of radioactive nuclides, and it is therefore important to understand the behavior of the EdZ or EDZ. We performed in situ experiments before, during, and after gallery excavation in galleries of 140 and 250 m in depth in an area of soft sedimentary rock in Japan. The results demonstrate that the extent of fractures induced by the gallery excavation related with EDZ was confined to 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 an unsaturated zone did not appear in the 250 m gallery.