Developing the soil moisture sensor using optical fiber technique (Joint research)

Komatsu, Mitsuru*; Nishigaki, Makoto*; Seno, Shoji*; Hirata, Yoichi*; Takenobu, Kazuyoshi*; Tagishi, Hirotaka*; Kunimaru, Takanori; Maekawa, Keisuke; Yamamoto, Yoichi; Toida, Masaru*; et al.

JAEA-Research 2012-001, 77 Pages, 2012/09

JAEA-Research-2012-001.pdf:4.85MB

This research focused on methods of estimating the amounts of groundwater recharge, which are normally required as upper boundary conditions in groundwater flow analyses, based on measurements of infiltrating water in the ground, to systematize the methods and establish systems which are stable and measurable on site over a long time. Regarding developing measurement systems, fiber-optic strain measurement methods that enable multiple-point and long-distance measurement were used for measuring three quantities: suction pressure, soil moisture and volumetric water content rate obtained by applying water absorption swelling material, and each measurement was discussed. The results showed that the fiber-optic soil aquameter has two types of practical application: one for measuring suction pressure (Type I), and the other for measuring volumetric water content rate obtained by applying water absorption swelling material (Type III). Furthermore, by using measurement instruments in actual fields, the validity of the two methods for estimating the rainfall infiltration capacities of shallow-layer soils, that is, estimating the capacities either directly by measurements of soil water or from unsaturated hydraulic conductivities, was confirmed.

Monitoring of pore water pressure and water content around a horizontal drift through excavation; Measurement at the 140m gallery in the Horonobe URL

Yabuuchi, Satoshi; Kunimaru, Takanori; Kishi, Atsuyasu*; Komatsu, Mitsuru*

Doboku Gakkai Rombunshu, C (Chiken Kogaku) (Internet), 67(4), p.464 - 473, 2011/11

http://joi.jlc.jst.go.jp/JST.JSTAGE/jscejge/67.464

Japan Atomic Energy Agency has been conducting the Horonobe Underground Research Laboratory (URL) project in Horonobe, Hokkaido, as a part of the research and development program on geological disposal of high-level radioactive waste. Pore water pressure and water content around a horizontal drift in the URL have been monitored for over 18 months since before the drift excavation was started. During the drift excavation, both pore water pressure and water content were decreasing. Pore water pressure has been still positive though it continued to decrease with its gradient gradually smaller after excavation, while water content turned to increase about 6 months after the completion of the excavation. It turned to fall again about 5 months later. An unsaturated zone may have been in homogeneously formed around the horizontal drift considering a degassing.

Experimental studies on unsaturated zone surrounding rock using Characterizing Laboratory test on Unsaturated zonE(CLUE)

Kikuchi, Hirohito*; Sugita, Yutaka; Chijimatsu, Masakazu*; Suzuki, Hideaki*; Komatsu, Mitsuru*; Nishigaki, Makoto*

JNC TN8400 2002-004, 97 Pages, 2002/02

JNC-TN8400-2002-004.pdf:5.43MB

In geological disposal of high-level radioactive waste (HLW), unsaturated zone will be developed around the disposal tunnel due to the construction of the tunnel. The development of the unsaturated zone would lead to the intrusion of the air into the surrounding rock and then oxygen would dissolve into ground water. Dissolved air affects the redox potential of the ground water and also oxidizes minerals existed in surrounding rock and changes their sorption capacity. These influences would change the geochemical conditions of the repository and affect the corrosion behavior of the overpack. Therefore, Characterizing Laboratory test on Unsaturated zonE (CLUE) was designed and assembled to understand the development process of the unsaturated zone. The CLUE is designed from the viewpoint of the hydraulic characteristics. CLUE has two test tanks. The test tank A uses glass beads to simulate rock mass, the test tank B uses rock block sample. Fundamental hydraulic data of the glass beads on saturation/unsaturation conditions for numerical analysis was obtained. Tests using the test tank A used the piezometer and frequency domain reflectometry (FDR) to measure the unsaturation behavior. From the results of the test tank A, the unsaturated zone was developed around the tunnel. The piezometer and FDR measured the distribution and the time history of the unsaturated zone well. In stable condition, measurement data was in good agreement with the analytical results.

Study on measurement of soil moisture content by using the optical fiber pressure sensor

Komatsu, Mitsuru*; Nishigaki, Makoto*; Seno, Shoji*; Hirata, Yoichi*; Kunimaru, Takanori

no journal, , 

no abstracts in English

Estimating of in-situ hydraulic conductivity related with evaluating of rainfall infiltration behavior in shallow ground

Komatsu, Mitsuru*; Nishigaki, Makoto*; Seno, Shoji*; Tagishi, Hirotaka*; Takenobu, Kazuyoshi*; Kishi, Atsuyasu

no journal, , 

Infiltration rate at the ground surface is one of the essential boundary conditions for a quantitative evaluation of groundwater flow. Conventional method for quantifying infiltration rate based on the water budget, however, includes significant uncertainties resulting from different types of quantities to be measured. In this study, focusing on a method where the infiltration rate is estimated directly from temporal changes in soil water contents in the region of interest, the measurement data was confirmed based on the unsaturated hydraulic tests. Then, the reliability of the measurement was verified by comparing the data to the laboratory test results and uncertainties associated with the measurements were quantified.

In-situ moisture monitoring methods for the sedimentary rocks as affected by groundwater salinity

Komatsu, Mitsuru*; Kishi, Atsuyasu; Tsukuda, Akie*

no journal, , 

In this study, with the goal of applicability an in-situ measurement technique for monitoring generation and extension of the unsaturated zone around a drift, a set of water content measurement was carried out for the core samples collected during the excavation of pilot survey drift in a sedimentary rock formation. For the drill core collected under brine environment the Horonobe deep underground laboratory, FDR-V method was applied. FDR-V measures complex permittivity from reflection characteristic in the coaxial cable tip using an electromagnetic wave with high frequency. The results showed that the effects of the salinity on the measurement were insignificant.