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.

Variation in fault hydraulic connectivity with depth in mudstone; An Analysis of poroelastic hydraulic response to excavation in the Horonobe URL

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

Geomechanics for Energy and the Environment, 31, p.100311_1 - 100311_13, 2022/09

https://doi.org/10.1016/j.gete.2022.100311

This study analyzed the long-term hydraulic pressure data during the excavation of Horonobe URL to estimate the variation of effective-hydraulic-conductivity. We performed the numerical simulation with the poroelastic effect for the estimation because the observed hydraulic pressure is highly affected by the Mandel-Cryer effect. The evaluation of the observed data based on our simulation results showed that the effective-hydraulic-conductivity gradually decreases from 400 m to 500 m in depth and is as low as the intact rock at depths greater than 500 m. Not only the analysis based on our simulation results but also the analysis based on analytical solution indicate the domain with different hydraulic properties in the Wakkanai Formation. These results suggest that the fracture-hydraulic-connectivity changes not abruptly but gradually over several tens of meters around the predicted boundary.

Evaluation of time lapse behavior of excavation damaged zone by first arrival tomography in Horonobe Underground Research Laboratory

Ozaki, Yusuke; Miyara, Nobukatsu

Proceedings of 14th SEGJ International Symposium (Internet), 4 Pages, 2021/10

https://doi.org/10.1190/segj2021-055.1

The drift excavation damages the intact rock around the drift wall and changes the physical properties there. The damaged domain is called excavation damaged zone (EDZ). The correct estimation of depth and the understanding of time lapse behavior of EDZ is required for the technology of drift closure. In Horonobe Underground Research Laboratory (URL), we repeatedly performed the travel time tomography to investigate the time lapse behavior of EDZ generated in soft sedimentary rock over time. For the analysis of the acquired data for the travel time tomography, we performed numerical simulation and estimated the conceivable change in the arrival time. The results of numerical simulation indicate that the shotcrete on the drift wall has the great impact on the travel time because of its high stiffness whereas the effect of shotcrete fixing the ray path might be the advantage for the monitoring purpose. The analysis of the data acquired at 350 m suggest that the significant change in EDZ that surpasses the observation limit was not recognized.

Thermally altered subsurface material of asteroid (162173) Ryugu

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.

Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03

https://doi.org/10.1038/s41550-020-01271-2

Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.

Quasifree neutron knockout reaction reveals a small -Orbital component in the Borromean nucleus B

Yang, Z. H.*; Kubota, Yuki*; Corsi, A.*; Yoshida, Kazuki; Sun, X.-X.*; Li, J. G.*; Kimura, Masaaki*; Michel, N.*; Ogata, Kazuyuki*; Yuan, C. X.*; et al.

Physical Review Letters, 126(8), p.082501_1 - 082501_8, 2021/02

AA2020-0819.pdf:1.29MB

https://doi.org/10.1103/PhysRevLett.126.082501

A quasifree (,) experiment was performed to study the structure of the Borromean nucleus B, which had long been considered to have a neutron halo. By analyzing the momentum distributions and exclusive cross sections, we obtained the spectroscopic factors for and orbitals, and a surprisingly small percentage of 9(2)% was determined for . Our finding of such a small component and the halo features reported in prior experiments can be explained by the deformed relativistic Hartree-Bogoliubov theory in continuum, revealing a definite but not dominant neutron halo in B. The present work gives the smallest - or -orbital component among known nuclei exhibiting halo features and implies that the dominant occupation of or orbitals is not a prerequisite for the occurrence of a neutron halo.

Poroelastic hydraulic-response of fractured mudstone to excavation in the Horonobe URL; As an indicator of fracture hydraulic-disconnectivity

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

Extended abstract of International Conference on Coupled Processes in Fractured Geological Media; Observation, Modeling, and Application (CouFrac 2020) (Internet), 4 Pages, 2020/11

We perform the numerical simulation of the response of hydraulic head observed in HDB-6 during the excavation of the Horonobe URL to verify the existence of low effective permeable domain in the subsurface. The low permeable domain as an intact rock due to the low hydraulic fracture connectivity is estimated to exist in the deep domain while the permeability of the shallow domain is relatively high due to the hydraulic fracture connectivity there. Our simulation shows that the observed hydraulic head is affected by the Mandel-Cryer effect due to the hydrogeological structure and the effect for the duration of over years requires the low permeability as an intact rock in the deep domain. These results verify the existence of the low effective permeable domain in the deep subsurface estimated by the previous study.

Transient ionization of the mesosphere during auroral breakup; Arase satellite and ground-based conjugate observations at Syowa Station

Kataoka, Ryuho*; Nishiyama, Takanori*; Tanaka, Yoshimasa*; Kadokura, Akira*; Uchida, Herbert Akihito*; Ebihara, Yusuke*; Ejiri, Mitsumu*; Tomikawa, Yoshihiro*; Tsutsumi, Masaki*; Sato, Kaoru*; et al.

Earth, Planets and Space (Internet), 71(1), p.9_1 - 9_10, 2019/12

https://doi.org/10.1186/s40623-019-0989-7

Transient ionization of the mesosphere was detected at around 65 km altitude during the isolated auroral expansion occurred at 2221-2226 UT on June 30, 2017. A general-purpose Monte Carlo particle transport code PHITS suggested that significant ionization is possible in the middle atmosphere due to auroral X-rays from the auroral electrons of 10 keV.

DECOVALEX-2019 Task C; GREET Intermediate report

Iwatsuki, Teruki; Onoe, Hironori; Ishibashi, Masayuki; Ozaki, Yusuke; Wang, Y.*; Hadgu, T.*; Jove-Colon, C. F.*; Kalinina, E.*; Hokr, M.*; Balvn, A.*; et al.

JAEA-Research 2018-018, 140 Pages, 2019/03

JAEA-Research-2018-018.pdf:40.68MB

DECOVALEX-2019 Task C aims to develop modelling and prediction methods using numerical simulation based on the water-filling experiment to examine the post drift-closure environment recovery processes. In this intermediate report, the results of Step 1 (Modelling and prediction of environmental disturbance by CTD excavation) are summarized from each of the research teams (JAEA, Sandia National Laboratories, Technical University of Liberec). Groundwater inflow rates to the tunnel during the excavation, hydraulic drawdown, and variation of chlorine concentration at monitoring boreholes in the vicinity of the tunnel were chosen as comparison metrics for Step1 by mutual agreement amongst the research teams. It is likely to be possible to foresee the scales of inflow rate and hydraulic drawdown based on a data from the pilot borehole by current simulation techniques.

Transition of near surface resistivity of tunnel wall during drift closure test

Ozaki, Yusuke; Ishibashi, Masayuki; Matsushita, Tomoaki*; Masumoto, Kazuhiko*; Imasato, Takehiko*

Proceedings of 13th SEGJ International Symposium (USB Flash Drive), 4 Pages, 2018/11

In the Mizunami Underground Research Laboratory, Groundwater REcoverty Experiment in Tunnel (GREET) is performed to understanding the recovery process of geological environment after the closure of drift. In this experiment, we performed 2D electrical resistivity surveys three times. First survey was performed before the closure of test drift. Second and third surveys were performed after the closure test. The first survey detected two layers conformation that consists of conductive and resistive zones at shallower and deeper part from the drift surface, respectively. These layers correspond to the shotcrete and host rock, respectively. Second and third measurements show that the conductive zone expanded to deeper resistive part while the shallower conductive part did not change. We concluded that we captured the saturation process of dried fractures near the drift wall by closure of drift as an electrical resistivity response.