Effect of fault activation on the hydraulic connectivity of faults in mudstone

Ono, Hirokazu; Ishii, Eiichi

Geomechanics for Energy and the Environment, 31, p.100317_1 - 100317_9, 2022/09

https://doi.org/10.1016/j.gete.2022.100317

Reaction and alteration of mudstone with Ordinary Portland Cement and Low Alkali Cement pore fluids

Bateman, K.; Amano, Yuki; Kubota, Mitsuru*; Ouchi, Yuji*; Tachi, Yukio

Minerals (Internet), 11(6), p.588_1 - 588_19, 2021/06

https://doi.org/10.3390/min11060588

Does fault activation affect the hydraulic disconnectivity of faults in mudstone?

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

Evaluating test conditions for in situ tracer migration test in fractured siliceous mudstone involving groundwater with dissolved gas

Takeda, Masaki; Ishii, Eiichi; Ono, Hirokazu; Kawate, Satoshi*

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 25(1), p.3 - 14, 2018/06

https://doi.org/10.3327/jnuce.25.1_3

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.

Mechanical and rheological characteristics of the siliceous mudstone at the Horonobe Underground Research Laboratory site

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.

Clay-based modeling approach to diffusion and sorption in the argillaceous rock from the Horonobe URL; Application to Ni(II), Am(III), and Se(IV)

Tachi, Yukio; Suyama, Tadahiro; Yotsuji, Kenji; Ishii, Yasuo; Takahashi, Hiroaki*

CMS Workshop Lectures, Vol.21, p.241 - 250, 2016/00

https://www.clays.org/other-cms-publications-wrksh21/

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.

Development of solute transport modelling for multiple flow paths around the faults in mudstone

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.