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Ono, Hirokazu; Ishii, Eiichi
Geomechanics for Energy and the Environment, 31, p.100317_1 - 100317_9, 2022/09
Times Cited Count:5 Percentile:63.89(Energy & Fuels)Bateman, K.; Murayama, Shota*; Hanamachi, Yuji*; Wilson, J.*; Seta, Takamasa*; Amano, Yuki; Kubota, Mitsuru*; Ouchi, Yuji*; Tachi, Yukio
Minerals (Internet), 11(9), p.1026_1 - 1026_23, 2021/09
Times Cited Count:2 Percentile:21.11(Geochemistry & Geophysics)Bateman, K.; Amano, Yuki; Kubota, Mitsuru*; Ouchi, Yuji*; Tachi, Yukio
Minerals (Internet), 11(6), p.588_1 - 588_19, 2021/06
Times Cited Count:4 Percentile:41.7(Geochemistry & Geophysics)Kamata, Kento*; Nara, Yoshitaka*; Matsui, Hiroya; Ozaki, Yusuke
Dai-15-Kai Iwa No Rikigaku Kokunai Shimpojiumu Koen Rombunshu (Internet), p.205 - 209, 2021/01
When considering the projects such as radioactive waste disposal, it is important to evaluate the confinement performance of underground substances in rock mass. However, the change in permeability of macro-fractured mudstone has not been sufficiently studied. Therefore, in this study, we investigated its effect on permeability by introducing a macro-fracture into a cylindrical specimen of mudstone distributed in the Horonobe area, Hokkaido. First, the hydraulic conductivity was measured by subjecting a specimen with a macro-fracture introduced by a brazilian test to a falling head permeability test. After that, it was compared with the hydraulic conductivity of the intact specimen measured by the transient pulse method. As a result, it was confirmed that the hydraulic conductivity was increased by about one order due to the introduction of macro-fracture. The increase rate of hydraulic conductivity obtained from the results of this research was smaller than that of previous researches using granite and basalt.
Ono, Hirokazu; Takeda, Masaki; Ishii, Eiichi
Extended abstract of International Conference on Coupled Processes in Fractured Geological Media; Observation, Modeling, and Application (CouFrac 2020) (Internet), 4 Pages, 2020/11
Aoyagi, Kazuhei; Ishii, Eiichi
Rock Mechanics and Rock Engineering, 52(2), p.385 - 401, 2019/02
Times Cited Count:16 Percentile:66.04(Engineering, Geological)Excavation of deep underground openings induces permeable fractures around the opening due to stress redistribution. Such a zone is called excavation damaged zone (EDZ). In a high-level radioactive waste disposal project, the EDZ might provide pathways for the migration of radionuclides around the facility. Thus, this study focused on the development of a method for estimating the highest potential hydraulic conductivity in the EDZ around a gallery in the Horonobe Underground Research Laboratory, Japan. Borehole televiewer surveys, rock core observations, and hydraulic tests were undertaken to investigate the extent and magnitude of hydraulic conductivity in the EDZ around the gallery. The observed extent of the EDZ shows good agreement with the EDZ estimated from hydro-mechanical coupling analysis. The measured hydraulic conductivities of the EDZ are within the range of those based on the Mean Stress Index (MSI), which is defined as the ratio of the effective mean stress derived from numerical analyses to the tensile strength of intact rock. Given that the rock mass is relatively homogeneous and artificial damage (e.g., blasting-induced damage) can be neglected, as in the Horonobe Underground Research Laboratory, the MSI model is likely to be applicable in estimating the highest potential hydraulic conductivity in the EDZ.
Takeda, Masaki; Ishii, Eiichi; Ono, Hirokazu; Kawate, Satoshi*
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 25(1), p.3 - 14, 2018/06
Fault zones and excavation damaged zones have the potential to act as flow paths, and the characterization of solute transport in such zones in mudstones is important for the safe geological disposal of radioactive waste. However, few in situ tracer migration tests have been conducted on fractures in mudstones. The Japan Atomic Energy Agency has conducted in situ tracer migration experiments using uranine, for fractures in siliceous mudstone of the Wakkanai Formation. 18 experiments were conducted under various conditions An injection flow rate that is slightly higher than the pumping flow rate is ideal for tracer migration experiments involving injection and pumping, as conducted in this study. In situ tracer migration experiments involving injection and pumping conducted in a groundwater environment with dissolved gases allow empirical evaluation of the relationship of the tracer recovery ratio and the groundwater degassing with the injection and pumping flow rate ratio. This evaluation is effective for the design of experimental conditions that account for degassing and ensure high levels of tracer recovery.
Aoyagi, Kazuhei; Ishii, Eiichi
Shigen, Sozai Koenshu (Internet), 4(2), 7 Pages, 2017/09
no abstracts in English
Hashiba, Kimihiro*; Fukui, Katsunori*; Sugita, Yutaka; Aoyagi, Kazuhei
Proceedings of ITA-AITES World Tunnel Congress 2017 (WTC 2017) (USB Flash Drive), 8 Pages, 2017/06
It is essential to understand the mechanical and rheological characteristics of diatomaceous and siliceous mudstones for the construction of underground structures and for the assessment of their long-term stability. In this study, the siliceous mudstone of the Wakkanai Formation was applied to various laboratory tests: compression test, creep test, relaxation test, drying shrinkage test, and slaking test. The test results showed that water has a major impact on the mechanical and rheological properties of the siliceous mudstone. In addition, water content at a tunnel wall was measured in the Horonobe URL. Comparing the results of the laboratory tests and the in situ measurement, the effect of water on the tunnel stability was discussed.
Sakurai, Akitaka; Aoyagi, Kazuhei; Fujita, Tomoo; Motoshima, Takayuki*
JAEA-Data/Code 2015-023, 46 Pages, 2016/02
In a high level radioactive waste (HLW) disposal project, it is necessary to investigate the long-term behavior of thermos-hydro-mechanical-chemical of the rock mass around the engineered barrier system of the HLW waste for the safety assessment of the disposal system. In addition, long-term stability of the rock mass around the galleries are required for the disposal facility. Considering these backgrounds, the authors measure the deformation behavior of the vertical pit drilled on the floor of the 350 m gallery in the Horonobe Underground Research Laboratory. In situ measurements of the deformation of the pit and rock mass around the pit was conducted to apply to the assessment of the long-term deformation behavior. The authors describe the drilling of the vertical pit, geological observation, specification of the measurement instrument, measurement method, and result of the measurement in this report.
Tachi, Yukio; Suyama, Tadahiro; Yotsuji, Kenji; Ishii, Yasuo; Takahashi, Hiroaki*
CMS Workshop Lectures, Vol.21, p.241 - 250, 2016/00
Sorption and diffusion of radionuclides in argillaceous rocks are key processes in the safe geological disposal. The diffusion and sorption behavior of Ni(II), Am(III) and Se(IV) in mudstone from the Horonobe URL were investigated by experimental and modeling approaches. Effective diffusivities obtained by the through-diffusion experiments were in the sequence of Cs, Ni, HTO, I, Se(SeO), Am(Am(CO)) by comparison with the previous study. The distribution coefficient values were consistent with those obtained by batch sorption tests. These results were interpreted by the clay-based modeling approach coupling the thermodynamic sorption model assuming key contributions of clays (smectite and illite) and the diffusion model assuming the electrical double layer theory and the simplified pore model with size distribution. This clay-based model could provide reasonable account of observed trends and could be basically applicable for various radionuclides.
Bateman, K.; Amano, Yuki; Tachi, Yukio
no journal, ,
Takeda, Masaki; Ono, Hirokazu; Tachi, Yukio; Murayama, Shota*
no journal, ,
This study characterized the solute transport properties of fault zone fractures in a mudstone by applying the modelling approach, which could be addressed heterogeneity in the fault zone fractures. Breakthrough curves (BTCs) derived from dipole tests were simulated with GoldSim code and the model assuming three flow paths individually consisted in the flow and stagnant domain. This modelling approach gave good agreement with the BTCs of uranine and Mo for pulse injection tests. However, there are some gaps of BTCs trend of uranine, Mo and Cs for continuous tests between in situ and simulation results. These gaps can be caused by larger tracer recovery in simulation results than tests results. We will continue to develope the more realistic model and optimal model parameters that can be appropriately treated to uncertainty of transport paths.