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Hata, Koji*; Niunoya, Sumio*; Aoyagi, Kazuhei; Miyara, Nobukatsu*
Journal of Rock Mechanics and Geotechnical Engineering, 16(2), p.365 - 378, 2024/02
Excavation of underground caverns, such as mountain tunnels and energy-storage caverns, may cause the damages to the surrounding rock as a result of the stress redistribution. In this influenced zone, new cracks and discontinuities are created or propagate in the rock mass. Therefore, it is effective to measure and evaluate the acoustic emission (AE) events generated by the rocks, which is a small elastic vibration, and permeability change. The authors have developed a long-term measurement device that incorporates an optical AE (O-AE) sensor, an optical pore pressure sensor, and an optical temperature sensor in a single multi-optical measurement probe (MOP). Japan Atomic Energy Agency has been conducting R&D activities to enhance the reliability of high-level radioactive waste (HLW) deep geological disposal technology. In a high-level radioactive disposal project, one of the challenges is the development of methods for long-term monitoring of rock mass behavior. Therefore, in January 2014, the long-term measurements of the hydro-mechanical behavior of the rock mass were launched using the developed MOP in the vicinity of 350 m below the surface at the Horonobe Underground Research Center. The measurement results show that AEs occur frequently up to 1.5 m from the wall during excavation. In addition, hydraulic conductivity increased by 2 to 4 orders of magnitude. Elastoplastic analysis revealed that the hydraulic behavior of the rock mass affected the pore pressure fluctuations and caused micro-fractures. Based on this, a conceptual model is developed to represent the excavation damaged zone (EDZ), which contributes to the safe geological disposal of radioactive waste.
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.
Motoshima, Takayuki*; Koike, Masashi*; Hagihara, Takeshi*; Aoyagi, Kazuhei
Dai-46-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koenshu (CD-ROM), p.208 - 213, 2019/01
The short step construction method is the standard construction method for deep shaft excavation. However, considering the shaft construction in the sedimentary rock widely distributed in Japan, the support concrete stress can become excessive especially when there are bad conditions such as low rock strength, anisotropic initial stress, or high ground pressure. In this research, we introduced the dual support design to the short step construction method in order to reduce the support stress, and confirmed the validity by three dimensional numerical analysis. Validation analysis was conducted using the in-situ data in the Horonobe Underground Research Project conducted by Japan Atomic Energy Agency.
Tokiwa, Tetsuya*; Tsusaka, Kimikazu*; Aoyagi, Kazuhei
International Journal of Civil Engineering, 16(4), p.371 - 381, 2018/04
Times Cited Count：3 Percentile：14.83(Engineering, Civil)Aoyagi, Kazuhei; Ishii, Eiichi; Fujita, Tomoo; Motoshima, Takayuki*
Dai-44-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koenshu (CD-ROM), p.313 - 318, 2016/01
The objective of this research is to investigate the extent and failure mechanism of an Excavation Damaged Zone (EDZ) induced around the East Access Shaft in the Horonobe Underground Research Laboratory. As a result of hydraulic tests, hydraulic conductivity within 2 m from the shaft wall was increased by 1 to 3 orders of magnitude. This result is consistent with the extent of the development of fractures detected by borehole televiewer surveys. Furthermore, the dominant failure mechanism of the fractures around the shaft wall was almost tensile; also these fractures were caused by the short-term excavation-induced unloading.
Yamasaki, Masanao*; Tsusaka, Kimikazu*; Otani, Tatsuhiko*; Shinji, Masato*
Doboku Gakkai Rombunshu, F2 (Chika Kukan Kenkyu) (Internet), 71(1), p.1 - 10, 2015/04
Japan Atomic Energy Agency has been constructed the Underground Research Laboratory in Hokkaido. In the shaft excavation, length, direction and aperture of geological observation are measured and analyzed in order to estimate rock permeability around lining. In this report, correlation between frequency of cracks and rock permeability based on crack tensor and stereology was discussed. Prediction equation of rock permeability from the frequency of cracks on the shaft wall was also proposed.
