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Aoyagi, Kazuhei; Ozaki, Yusuke; Tamura, Tomonori; Ishii, Eiichi
Proceedings of 4th International Conference on Coupled Processes in Fractured Geological Media; Observation, Modeling, and Application (CouFrac2024) (Internet), 10 Pages, 2024/11
In high-level radioactive waste disposal, it is crucial to estimate the transmissivity of gallery excavation-induced fractures, i.e., excavation damaged zone (EDZ) fractures, because EDZ fractures can be a radionuclide migration pathway after the backfilling of the facility is completed. From previous research, the transmissivity of the fracture can be estimated through the empirical equation using the parameter ductility index (DI), which corresponds to the effective mean stress normalized to the tensile strength of the rock. In this research, we performed a hydromechanical coupling analysis of a gallery excavation at the Horonobe Underground Research Laboratory to estimate the transmissivity of the EDZ fracture before the excavation. At first, we simulated the gallery excavation at 350 m and showed that the measured transmissivity was within the range of the estimated transmissivity using the DI. After that, we also predicted the excavation of a gallery at 500 m by setting the hydromechanical parameters acquired from the laboratory tests before the excavation. The estimated transmissivity at 500 m was one order of magnitude less than that at 350 m. This result might be related to the closure of the fracture under high-stress conditions and low rock strength.
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.