Rock strength and stress dependence of local flow-path connectivity within faults or fractures; A Preliminary overview of virtual and in-situ hydraulic tests

Ishii, Eiichi; Ozaki, Yusuke; Aoyagi, Kazuhei; Sugawara, Kentaro*

Hydrogeology Journal, 33(1), p.63 - 85, 2025/02

https://doi.org/10.1007/s10040-024-02859-y

This study performed virtual packer tests on modeled single fractures on computer and derived the relationship between flow dimension and mappable indicator, DI, which is defined by the mean stress, groundwater pressure, and rock tensile strength. The greater DI results in the smaller flow area in faults or fractures, subject to fracture-normal closure. Comparing the derived relationship with results from in situ hydraulic tests on natural faults in rock with few fracture-mineral-fillings revealed that flow-path connectivity is high (flow dimension 1.5) when DI was 2.0 while was low (flow dimension 1.5) when DI was 2.0. This relationship was valid even when DI was varied, or faults were sheared, during injection tests on faults, and even in rock with abundant fracture-mineral-fillings. However, flow-path connectivity in minor fractures far from faults could be also low even when DI was 2.0 probably due to poor connection to the main fault network or sealing effects of fracture-mineral-fillings. When the permeability of intact rock is high, flow-path connectivity in fractures was high even when DI was 2.0. These findings can be helpful to map the spatial distribution of flow-path connectivity in faults or fractures from limited borehole data.

Current status and future prospects of the Horonobe International Project (HIP), 2; Task A: Solute transport experiment with model testing

Ozaki, Yusuke

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 31(2), p.128 - 133, 2024/12

https://nuce.aesj.or.jp/jnuce/vol31/jnuce-vol31-2-p128-133.pdf

Task A of the Horonobe International Project (HIP) aims to investigate the characteristics of solute transport of the Koetoi Formation at 250 m stage of the Horonobe underground research laboratory (URL). The objective of this task is to develop a modeling approach of solute transport considering actual phenomena occurring in the rock based on in-situ tracer experiments along with the discussion on transferability of data and modeling approach from different geological environment. Phase 1 of task A is divided into four subtasks of planning of in situ experiments, laboratory experiments, field experiments, and modeling. These subtasks are tackled by participating organizations as collaborative research, and I present the current situation of each subtask and our cooperation.

Transmissivity prediction of the Excavation Damaged Zone fracture around the gallery at 500 m at the Horonobe Underground Research Laboratory

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.

Biofilm formation on excavation damaged zone fractures in deep neogene sedimentary rock

Hirota, Akinari*; Kozuka, Mariko*; Fukuda, Akari*; Miyakawa, Kazuya; Sakuma, Keisuke; Ozaki, Yusuke; Ishii, Eiichi; Suzuki, Yohei*

Microbial Ecology, 87, p.132_1 - 132_15, 2024/10

https://doi.org/10.1007/s00248-024-02451-7

Deep underground galleries are used to access the deep biosphere in addition to mining and other engineering applications such as geological disposal of radioactive wastes. Fracture networks developed in the excavation damaged zone (EDZ) are concerned to accelerate mass transport, where microbial colonization might be possible due to the availability of space and nutrients. In this study, microbial biofilms at EDZ fractures were investigated by drilling from a 350-m deep gallery and subsequent borehole logging at the Horonobe underground research laboratory (URL). By using microscopic and spectroscopic techniques, the dense colonization of microbial cells was demonstrated at the surfaces of the EDZ fractures with high hydraulic conductivities. 16S rRNA gene sequence analysis revealed the dominance of gammaproteobacterial lineages, the cultivated members of which are aerobic methanotrophs. Near-complete Horonobe groundwater genomes affiliated within the methanotrophic lineages were fully equipped with genes involved in aerobic methanotrophy. Although the mediation of aerobic methanotrophy remains to be demonstrated, microbial O production was supported by the presence of genes in the near-complete genomes, such as catalase and superoxide dismutase that produce O from reactive oxygen species and a nitric oxide reductase gene with the substitutions of amino acids in motifs. It is concluded that the EDZ fractures provide energetically favorable subsurface habitats to microorganisms.

Observation of high-pressure polymorphs in bulk silicon formed at relativistic laser intensities

Rapp, L.*; Matsuoka, Takeshi*; Firestein, K. L.*; Sagae, Daisuke*; Habara, Hideaki*; Mukai, Keiichiro*; Tanaka, Kazuo*; Gamaly, E. G.*; Kodama, Ryosuke*; Seto, Yusuke*; et al.

Physical Review Research (Internet), 6(2), p.023101_1 - 023101_18, 2024/04

https://doi.org/10.1103/PhysRevResearch.6.023101

It is generally known that irradiating a solid surface with a laser pulse of ultra-relativistic intensity generates a plasma on the surface, which in turn creates an ultrahigh pressure inside. In this study, the crystal structure analysis of high-pressure phases generated inside silicon single-crystals irradiated by this laser was performed using the diffraction system at the Stress and Imaging apparatus of BL22XU, which is a JAEA-BL. The results obtained confirm the existence of high-pressure phases that silicon is said to possess: body-centered, rhombohedral, hexagonal, and tetragonal phases in the interior. We can get the results that the crystal structure of silicon polymorphs of being include body-centered, rhombohedral, hexagonal-diamond, tetragonal exists. In the future, we will accumulate data and apply them to control the internal structure, strength, and functionality of materials.

Influence of clay-doped water on permeability in granite rock mass

Nara, Yoshitaka*; Kashiwaya, Koki*; Oketani, Kazuki*; Fujii, Hirokazu*; Zhao, Y.*; Kato, Masaji*; Aoyagi, Kazuhei; Ozaki, Yusuke; Matsui, Hiroya; Kono, Masanori*

Zairyo, 73(3), p.220 - 225, 2024/03

https://doi.org/10.2472/jsms.73.220

The fractures in the rock are the main pass of groundwater flow and solute transport. The filling of fine-grained particle, such as clay minerals, was confirmed to decrease the permeability of rock by laboratory experiment. This research aimed to verify the occurrence of the phenomena in the field. The water containing the clay minerals was injected into the rock at the 200m stage of the Mizunami Underground research laboratory. The hydraulic conductivity decreased two order before and after the injection. This result suggested that the decrease of hydraulic conductivity by the filling of fine-grained particle in the fractures occurred in the real field.

First-arrival traveltime tomography for monitoring the excavation damaged zone in the Horonobe Underground Research Laboratory

Ozaki, Yusuke

Rock Mechanics Bulletin (Internet), 2(3), p.100057_1 - 100057_12, 2023/07

https://doi.org/10.1016/j.rockmb.2023.100057

In this study, a series of data repeatedly acquired by first arrival traveltime tomography for seven years was analyzed to investigate the time-lapse behavior of excavation damaged zone (EDZ) at 350 m stage in the Horonobe Underground Research Laboratory. The data was highly affected by the shotcrete on the drift wall, and a priori information on the structure of shotcrete was incorporated into the inversion process to alleviate the effect. In addition, time-lapse inversion was applied to trace the change in P-wave velocity in time. Our inversion results indicated that time dependent change of EDZ was not recognized under open-drift condition during the period in the site.

Crystallinity in periodic nanostructure surface on Si substrates induced by near- and mid-infrared femtosecond laser irradiation

Miyagawa, Reina*; Kamibayashi, Daisuke*; Nakamura, Hirotaka*; Hashida, Masaki*; Zen, H.*; Somekawa, Toshihiro*; Matsuoka, Takeshi*; Ogura, Hiroyuki*; Sagae, Daisuke*; Seto, Yusuke*; et al.

Scientific Reports (Internet), 12, p.20955_1 - 20955_8, 2022/12

https://doi.org/10.1038/s41598-022-25365-1

We evaluated Laser-Induced Periodic Surface Structure (LIPSS) crystal structures using the stress imaging station at BL22XU of JAEA-BL on SPring-8. Crystallization of LIPPS was used different two types laser these are Ti:Sapphire laser (wavelength: 800 nm) and MIR-FEL (mid-infrared free electron laser, wavelength 11.4 m). These lasers are different in the laser pulse structure and the wavelength. We investigated on the effects of formed LIPSS crystallization using different kind of laser. Measured synchrotron X-ray energy is 30 keV and beam size is 20 m. Detector of diffracted X-ray is two-dimensional detector (PILATUS300K, DECTRIS). LIPSS formed using Ti:Sapphire laser has deformed structure with good crystallinity. LIPSS formed using MIR-FEL has dislocation or fault without structural stress. These results show depending on select of laser forming LIPPS structure. These information becomes important a point of the functional application of LIPSS.

Study on the evaluation method to determine the radioactivity concentration in radioactive waste on Oarai Research and Development Institute (FY2020)

Asakura, Kazuki; Shimomura, Yusuke; Donomae, Yasushi; Abe, Kazuyuki; Kitamura, Ryoichi; Miyakoshi, Hiroyuki; Takamatsu, Misao; Sakamoto, Naoki; Isozaki, Ryosuke; Onishi, Takashi; et al.

JAEA-Review 2021-020, 42 Pages, 2021/10

JAEA-Review-2021-020.pdf:2.95MB

The disposal of radioactive waste from the research facility need to calculate from the radioactivity concentration that based on variously nuclear fuels and materials. In Japan Atomic Energy Agency Oarai Research and Development Institute, the study on considering disposal is being advanced among the facilities which generate radioactive waste as well as the facilities which process radioactive waste. This report summarizes a study result in FY2020 about the evaluation method to determine the radioactivity concentration in radioactive waste on Oarai Research and Development Institute.

Development of modeling methodology for hydrogeological heterogeneity of the deep fractured granite in Japan

Onoe, Hironori; Ishibashi, Masayuki*; Ozaki, Yusuke; Iwatsuki, Teruki

International Journal of Rock Mechanics and Mining Sciences, 144, p.104737_1 - 104737_14, 2021/08

https://doi.org/10.1016/j.ijrmms.2021.104737

In this study, we investigated the methodology of modeling for fractured granite around the drift at a depth of 500 m in the Mizunami Underground Laboratory, Japan as a case study. As a result, we developed the fracture modeling method to estimate not only geological parameters of fractures but also hydraulic parameters based on the reproducibility of trace length distribution of fractures. By applying this modeling method, it was possible to construct a Discrete Fracture Network (DFN) model that can accurately reproduce the statistical characteristics of fractures.