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Journal Articles

Characterizing the permeability of drillhole core samples of Toki granite, central Japan to identify factors influencing rock-matrix permeability

Kubo, Taiki*; Matsuda, Norihiro*; Kashiwaya, Koki*; Koike, Katsuaki*; Ishibashi, Masayuki; Tsuruta, Tadahiko; Matsuoka, Toshiyuki; Sasao, Eiji; Lanyon, G. W.*

Engineering Geology, 259, p.105163_1 - 105163_15, 2019/09

 Times Cited Count:5 Percentile:57.99(Engineering, Geological)

Rock matrix permeability is mainly controlled by microcracks. This study aims to identify the factors influencing the permeability of the Toki granite, central Japan. Permeability of core samples, measured by a gas permeameter, largely increases in the fault and fracture zones. Although a significant correlation is identified between permeability and P-wave velocity, this correlation is enhanced by classifying the samples into two groups by the Mn/Fe concentration ratio. Thus, lithofacies is another control factor for permeability due to the difference in mineral composition. Moreover, permeability shows significant negative and positive correlations with Si and Ca concentrations, respectively. These concentrations are probably affected by dissolution of silicate minerals and calcite generation in the hydrothermal alteration process. Therefore, a combination of hydrothermal alteration and strong faulting are the predominant processes for controlling permeability.

Journal Articles

Precipitation of minerals on rock kept in water with different calcium ion concentrations

Nara, Yoshitaka*; Kuwatani, Ryuta*; Kono, Masanori*; Sato, Toshinori; Kashiwaya, Koki*

Zairyo, 67(7), p.730 - 737, 2018/07

Information of confining ability of rock is important for the geological disposal of radioactive wastes. To maintain or improve the confining ability of rocks, it is important to seal pores and cracks. In this study, we investigated the precipitation of minerals on the rock surface. As rock samples, we used Berea sandstone and Toki granite in this study. It was shown that precipitation occurred on the surface of rock specimens kept in calcium hydroxide solution for 1 month if the concentration was high. Specifically, if the concentration of calcium hydroxide solution was higher than 300 mg/l, the precipitation occurred obviously. After keeping rock specimens in calcium hydroxide solution, the weight of the rock samples increased and the concentration of calcium ion decreased by the precipitation. It is considered that the calcium ion in water was used for the precipitation on rock surfaces. Since the precipitation has been recognized for rock surfaces, it is possible to seal pores and cracks in rocks. Therefore, it is also possible to keep or decrease the permeability of rocks by the precipitation of calcium compounds.

Journal Articles

Cross-checking groundwater age by $$^{4}$$He and $$^{14}$$C dating in a granite, Tono area, central Japan

Hasegawa, Takuma*; Nakata, Kotaro*; Tomioka, Yuichi*; Goto, Kazuyuki*; Kashiwaya, Koki*; Hama, Katsuhiro; Iwatsuki, Teruki; Kunimaru, Takanori*; Takeda, Masaki

Geochimica et Cosmochimica Acta, 192, p.166 - 185, 2016/11

 Times Cited Count:5 Percentile:29.75(Geochemistry & Geophysics)

Groundwater dating was performed simultaneously by the $$^{4}$$He and $$^{14}$$C methods in granite of the Tono area in central Japan. Groundwater was sampled at 30 packed-off sections of six 1000-m boreholes. $$^{4}$$He concentrations increased and $$^{14}$$C concentrations decreased along a groundwater flow path on a topographic gradient. $$^{4}$$He ages were calculated by using the in situ $$^{4}$$He production rate derived from the porosity, density, and U and Th content of the rock, neglecting external flux. The linear relation between the $$^{4}$$He ages and the noncorrected $$^{14}$$C ages, except in the discharge area. Simultaneous measurements make it feasible to estimate the accumulation rate of $$^{4}$$He and initial dilution of $$^{14}$$C, which cannot be done with a single method. Cross-checking groundwater dating has the potential to provide more reliable groundwater ages.

Oral presentation

Central Research Institute of Electric Power Industry - Japan Atomic Energy Agency Joint Research; A Study of the hydraulic properties and transport characteristics around the Mizunami Underground Laboratory Project

Hasegawa, Takuma*; Nakata, Kotaro*; Tomioka, Yuichi*; Goto, Kazuyuki*; Kashiwaya, Koki*; Hama, Katsuhiro

no journal, , 

The groundwater flow velocity is one of the important items in the safety assessment for the HLW disposal. Generally, it is too difficult to measure the groundwater flow velocity directly. Therefore, to determine the groundwater age by radio active isotopes are effective. However, there are some problems to apply the metrology to the natural samples. For example, because the ratio of Carbon isotope changes by dissolving of the carbonate mineral and resolving the organic materials, the development of the technique for correcting this is needed. In this study, the groundwater ages are measured by $$^{4}$$He and $$^{14}$$C, etc. and compared these results as a joint research with Central Research Institute of Electric Power Industry.

Oral presentation

Sorption behaviors of cations into clay minerals occurred in fault

Watanabe, Yusuke; Kashiwaya, Koki*

no journal, , 

no abstracts in English

Oral presentation

Sorption behaviors of cations into altered rock occurred in fault

Watanabe, Yusuke; Kashiwaya, Koki*

no journal, , 

no abstracts in English

Oral presentation

Sorption behaviors of Cs and Eu onto altered rock formed around fault

Watanabe, Yusuke; Kashiwaya, Koki*

no journal, , 

no abstracts in English

Oral presentation

Estimation of fault function as a barrier on nuclide migration using hypothetical hydrogeological models

Aoki, Tsuikimaru*; Kashiwaya, Koki*; Watanabe, Yusuke; Koike, Katsuaki*

no journal, , 

no abstracts in English

Oral presentation

Numerical modeling of pore water migration and water quality evolution due to compaction and diagenesis processes of sedimentary rock

Komura, Yuto*; Kashiwaya, Koki*; Miyakawa, Kazuya; Nakata, Kotaro*; Koike, Katsuaki*

no journal, , 

no abstracts in English

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