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JAEA Reports

Horonobe Underground Research Laboratory Project; Investigation report for the 2019 fiscal year

Nakayama, Masashi; Saiga, Atsushi

JAEA-Review 2020-042, 116 Pages, 2021/01

JAEA-Review-2020-042.pdf:10.33MB

The Horonobe Underground Research Laboratory Project will be conducted in three phases, namely "Phase 1: Surface-based investigations", "Phase 2: Construction Phase" (investigations during construction of the underground facilities) and "Phase 3: Operation phase" (research in the underground facilities). This report summarizes the results of the investigations for the 2019 fiscal year (2019/2020). The investigations, which are composed of "Geoscientific research" and "R and D on geological disposal technology", were carried out according to "Horonobe Underground Research Laboratory Project Investigation Program for the 2019 fiscal year". The results of these investigations, along with the results which were obtained in other departments of Japan Atomic Energy Agency (JAEA), are properly offered to the implementations and the safety regulations. For the sake of this, JAEA has proceeded with the project in collaboration with experts from domestic and overseas research organizations.

JAEA Reports

Backfill material characteristics using the bentonite/excavated rock mixture in the Horonobe Underground Research Laboratory Project (Contract research)

Sugita, Yutaka; Kikuchi, Hirohito*; Hoshino, Emiko*

JAEA-Data/Code 2020-017, 39 Pages, 2021/01

JAEA-Data-Code-2020-017.pdf:2.96MB

In Japan, high-level radioactive waste (HLW) will be buried in a purpose built repository in deep underground. In the vertical disposal concept of HLW, nuclear waste canisters will be emplaced in excavated vertical disposal holes, surrounded by bentonite/sand mixture. And the galleries will be backfilled with bentonite/excavated rock mixture, which will be isolated with a concrete plug. Japan Atomic Energy Agency has performed swelling test, permeability test, thermal property measurement, uniaxial compression test, water potential measurement and infiltration tests to identify coupled thermal-hydraulic-mechanical-chemical behavior that will operate in the backfill material using excavated rock in the Horonobe Underground Research Laboratory (URL). The obtained data will be used to support an ongoing full scale, in-situ experiment being conducted in the Horonobe URL.

JAEA Reports

Horonobe Underground Research Laboratory Project; Investigation program for the 2020 fiscal year

Nakayama, Masashi; Saiga, Atsushi

JAEA-Review 2020-022, 34 Pages, 2020/11

JAEA-Review-2020-022.pdf:3.99MB

The Horonobe Underground Research Laboratory (URL) Project is being pursued by the Japan Atomic Energy Agency (JAEA) to enhance the reliability of relevant disposal technologies for geological disposal of High-level Radioactive Waste through investigations of the deep geological environment within the host sedimentary rock at Horonobe Town in Hokkaido, north Japan. The investigations will be conducted in three phases, namely "Phase 1: Surface-based investigations", "Phase 2: Construction phase" (investigations during construction of the underground facilities) and "Phase 3: Operation phase" (research in the underground facilities). According to the research plan described in the 3rd Mid- and Long- term Plan of JAEA, "Demonstration of EBS in geological environment", "Demonstration of disposal concept", and "Validation of buffer capacity of the sedimentary rock to tectonism" are important issues of the Horonobe URL Project, and schedule of future research and backfill plans of the URL will be decided by the end of 2019 Fiscal Year. JAEA summarizes the research and development activities of the important issues carried out during the 3rd Mid- and Long-term Plan, and set out three important issues after 2020 fiscal year. After consultation with Hokkaido and Horonobe town, JAEA formulated the Horonobe underground research plan after 2020 fiscal year within the 3rd and 4th Mid- and Long-term Plan. This report summarizes the investigation program for the 2020 fiscal year (2020/2021).

JAEA Reports

Long term monitoring and evaluation of the excavation damaged zone induced around the wall of the shaft applying optical fiber sensor (Cooperative research)

Hata, Koji*; Niunoya, Sumio*; Uyama, Masao*; Nakaoka, Kenichi*; Fukaya, Masaaki*; Aoyagi, Kazuhei; Sakurai, Akitaka; Tanai, Kenji

JAEA-Research 2020-010, 142 Pages, 2020/11

JAEA-Research-2020-010.pdf:13.74MB
JAEA-Research-2020-010-appendix(DVD-ROM).zip:149.9MB

In the geological disposal study of high-level radioactive waste, it is suggested that the excavation damaged zone (EDZ) which is created around a tunnel by the excavation will be possible to be one of the critical path of radionuclides. Especially, the progress of cracks in and around the EDZ with time affects the safety assessment of geological disposal and it is important to understand the hydraulic change due to the progress of cracks in and around EDZ. In this collaborative research, monitoring tools made by Obayashi Corporation were installed at a total of 9 locations in the three boreholes near the depth of 370 m of East Shaft at the Horonobe Underground Research Laboratory constructed in the Neogene sedimentary rock. The monitoring tool consists of one set of "optical AE sensor" for measuring of the mechanical rock mass behavior and "optical pore water pressure sensor and optical temperature sensor" for measuring of groundwater behavior. This tool was made for the purpose of selecting and analyzing of AE signal waveforms due to rock fracture during and after excavation of the target deep shaft. As a result of analyzing various measurement data including AE signal waveforms, it is able to understand the information on short-term or long-term progress of cracks in and around EDZ during and after excavation in the deep shaft. In the future, it will be possible to carry out a study that contributes to the long-term stability evaluation of EDZ in sedimentary rocks in the deep part of the Horonobe Underground Research Laboratory by evaluation based on these analytical data.

JAEA Reports

Investigation of deterioration and effect on geological environment of low alkaline cement in Horonobe Underground Research Laboratory

Nakayama, Masashi

JAEA-Data/Code 2020-009, 98 Pages, 2020/09

JAEA-Data-Code-2020-009.pdf:6.06MB
JAEA-Data-Code-2020-009-appendix1(DVD-ROM).zip:172.11MB
JAEA-Data-Code-2020-009-appendix2-1(DVD-ROM).zip:468.85MB
JAEA-Data-Code-2020-009-appendix2-2(DVD-ROM).zip:102.94MB
JAEA-Data-Code-2020-009-appendix2-3(DVD-ROM).zip:141.88MB
JAEA-Data-Code-2020-009-appendix2-4(DVD-ROM).zip:141.6MB

Japan Atomic Energy Agency (JAEA) has developed a low alkaline cement, named as HFSC (Highly Fly-ash contained Silicafume Cement), in order to decrease the effect on geological environment of cementitious material. HFSC was used experimentally as the shotcrete (140m, 250m and 350m depth gallery) and lining concrete (GL-374m to GL-380m of east access shaft) in construction part of Horonobe URL. In order to evaluate the effect of HFSC on the surrounding rock and groundwater, concrete and rock cores were periodically sampled from the site where the in-situ construction test was conducted, and various analyzes were conducted. Ordinary Portland Cement (OPC) was used for part of 140m depth gallery, and the same analysis as HFSC was conducted, in order to compare the effect of OPC and HFSC. This report summarizes the results of analyzes conducted on core samples from 2009 to 2018.

JAEA Reports

Synthesis report on the R&D for the Horonobe Underground Research Laboratory; Project carried out during fiscal years 2015-2019

Nakayama, Masashi; Saiga, Atsushi; Kimura, Shun; Mochizuki, Akihito; Aoyagi, Kazuhei; Ono, Hirokazu; Miyakawa, Kazuya; Takeda, Masaki; Hayano, Akira; Matsuoka, Toshiyuki; et al.

JAEA-Research 2019-013, 276 Pages, 2020/03

JAEA-Research-2019-013.pdf:18.72MB

The Horonobe Underground Research Laboratory (URL) Project is being pursued by the Japan Atomic Energy Agency (JAEA) to enhance the reliability of relevant disposal technologies for geological disposal of High-level Radioactive Waste through investigations of the deep geological environment within the host sedimentary rock at Horonobe Town in Hokkaido, north Japan. The investigations will be conducted in three phases, namely "Phase 1: Surface based investigations", "Phase 2: Construction phase" (investigations during construction of the underground facilities) and "Phase 3: Operation phase" (research in the underground facilities). According to the research plan described in the 3rd Mid- and Long- term Plan of JAEA, "Near-field performance study", "Demonstration of repository design option", and "Verification of crustal-movement buffering capacity of sedimentary rocks" are important issues of the Horonobe URL Project, and schedule of future research and backfill plans of the project will be decided by the end of 2019 Fiscal Year. The present report summarizes the research and development activities of these 3 important issues carried out during 3rd Medium to Long-term Research Phase.

JAEA Reports

Earthquake observation data collection in the Horonobe Underground Research Laboratory Project (Phase II)

Miyara, Nobukatsu; Matsuoka, Toshiyuki

JAEA-Data/Code 2019-013, 8 Pages, 2020/01

JAEA-Data-Code-2019-013.pdf:1.45MB
JAEA-Data-Code-2019-013-appendix(DVD-ROM)1.zip:239.91MB
JAEA-Data-Code-2019-013-appendix(DVD-ROM)10.zip:346.69MB
JAEA-Data-Code-2019-013-appendix(DVD-ROM)11.zip:237.95MB
JAEA-Data-Code-2019-013-appendix(DVD-ROM)12.zip:335.05MB
JAEA-Data-Code-2019-013-appendix(DVD-ROM)13.zip:335.0MB
JAEA-Data-Code-2019-013-appendix(DVD-ROM)2.zip:433.26MB
JAEA-Data-Code-2019-013-appendix(DVD-ROM)3.zip:360.88MB
JAEA-Data-Code-2019-013-appendix(DVD-ROM)4.zip:292.24MB
JAEA-Data-Code-2019-013-appendix(DVD-ROM)5.zip:315.31MB
JAEA-Data-Code-2019-013-appendix(DVD-ROM)6.zip:426.42MB
JAEA-Data-Code-2019-013-appendix(DVD-ROM)7.zip:286.49MB
JAEA-Data-Code-2019-013-appendix(DVD-ROM)8.zip:187.61MB
JAEA-Data-Code-2019-013-appendix(DVD-ROM)9.zip:826.1MB

As part of the research and development program on the geological disposal of high-level radioactive waste (HLW), the Horonobe Underground Research Center, a division of the Japan Atomic Energy Agency (JAEA), is implementing the Horonobe Underground Research Laboratory Project (Horonobe URL Project) with the aim at investigating sedimentary rock formations. This data collection is a compilation of Earthquake observation data acquired in the Horonobe Underground Research Project (Phase II).

JAEA Reports

The In-situ experiment for performance confirmation of engineered barrier system at Horonobe Underground Research Laboratory; Installation of engineered barrier system and backfilling the test niche at the 350m gallery

Nakayama, Masashi; Ono, Hirokazu

JAEA-Research 2019-007, 132 Pages, 2019/12

JAEA-Research-2019-007.pdf:11.29MB
JAEA-Research-2019-007-appendix(CD-ROM).zip:39.18MB

The Horonobe Underground Research Laboratory (URL) Project has being pursued by Japan Atomic Energy Agency (JAEA) to enhance the reliability of relevant disposal technologies through investigations of the deep geological environment within the host sedimentary formation at Horonobe, northern Hokkaido. The URL Project consists of two major research areas, "Geoscientific Research" and "Research and Development on Geological Disposal Technologies". The in-situ experiment for performance confirmation of engineered barrier system (EBS experiment) had been prepared from 2013 to 2014 fiscal year at GL-350m gallery, and heating by electric heater in simulated overpack had started in January, 2015. One of objectives of the EBS experiment is acquiring data concerned with Thermal-Hydrological-Mechanical-Chemical (THMC) coupled behavior. These data will be used in order to confirm the performance of engineered barrier system. This report shows following works had carried out at the GL-350 m gallery. Excavation of a test niche and a test pit, Setting buffer material blocks and a simulated overpack into the test pit, Backfilling the niche by compaction backfilling material and setting backfilling material blocks, Casting concrete type plug and contact grouting, Consolidate measurement system and start measuring.

JAEA Reports

Horonobe Underground Research Laboratory Project; Investigation program for the 2019 fiscal year

Aoyagi, Kazuhei

JAEA-Review 2019-008, 20 Pages, 2019/07

JAEA-Review-2019-008.pdf:3.33MB

As part of the research and development program on the geological disposal of high-level radioactive waste (HLW), the Horonobe Underground Research Center, a division of the Japan Atomic Energy Agency (JAEA), is implementing the Horonobe Underground Research Laboratory Project (Horonobe URL Project) with the aim at investigating sedimentary rock formations. According to the research plan described in the 3rd Mid- and Long- term Plan of JAEA, "Near-field performance study", "Demonstration of repository design option", and "Verification of crustal-movement buffering capacity of sedimentary rocks" are the top priority issues of the Horonobe URL Project, and schedule of future research and backfill plans of the project will be decided by the end of 2019 Fiscal Year. The Horonobe URL Project is planned to extend over a period of about 20 years. The investigations will be conducted in three phases, namely "Phase 1: Surface-based investigations", "Phase 2: Construction phase" (investigations during construction of the underground facilities) and "Phase 3: Operation phase" (research in the underground facilities). This report summarizes the investigation program for the 2019 fiscal year (2019/2020). In the 2019 fiscal year, investigations in "geoscientific research", including "development of techniques for investigating the geological environment", "development of engineering techniques for use in the deep underground environment" and "studies on the long-term stability of the geological environment", are continuously carried out. Investigations in "research and development on geological disposal technology", including "improving the reliability of disposal technologies" and "enhancement of safety assessment methodologies", are also continuously carried out.

JAEA Reports

Horonobe Underground Research Laboratory Project; Investigation report for the 2017 fiscal year

Hanamuro, Takahiro; Saiga, Atsushi

JAEA-Review 2018-027, 125 Pages, 2019/02

JAEA-Review-2018-027.pdf:21.79MB

The Horonobe Underground Research Laboratory Project is planned to extend over a period 20 years. The investigations will be conducted in three phases, namely "Phase 1: Surface-based investigations", "Phase 2: Construction Phase" (investigations during construction of the underground facilities) and "Phase 3: Operation phase" (research in the underground facilities). This report summarizes the results of the investigations for the 2017 fiscal year (2017/2018). The investigations, which are composed of "Geoscientific research" and "R&D on geological disposal technology", were carried out according to "Horonobe Underground Research Laboratory Project Investigation Program for the 2017 fiscal year". The results of these investigations, along with the results which were obtained in other departments of Japan Atomic Energy Agency (JAEA), are properly offered to the implementations and the safety regulations. For the sake of this, JAEA has proceeded with the project in collaboration with experts from domestic and overseas research organizations.

JAEA Reports

Data of tracer migration test and borehole investigations for fracture zone in the Wakkanai formation at Horonobe Underground Research Laboratory

Tsushima, Masahito*; Takeda, Masaki; Ono, Hirokazu

JAEA-Data/Code 2018-008, 78 Pages, 2018/10

JAEA-Data-Code-2018-008.pdf:6.73MB
JAEA-Data-Code-2018-008(errata).pdf:0.11MB
JAEA-Data-Code-2018-008-appendix(DVD-ROM).zip:263.67MB

Japan Atomic Energy Agency (JAEA) has been conducting "geoscientific study" and "research and development on geological disposal" in the Horonobe Underground Research Laboratory (URL). In-situ tracer migration test for fracture and matrix in the argillaceous rock, called for Wakkanai formation, has been conducted in the Horonobe URL project. This report summarizes data of borehole investigations and tracer migration test for fracture zone.

JAEA Reports

The In-situ experiment for overpack corrosion at Horonobe Underground Research Laboratory; Production and setting simulated overpack, buffer material blocks and heater

Nakayama, Masashi

JAEA-Technology 2018-006, 43 Pages, 2018/08

JAEA-Technology-2018-006.pdf:5.32MB
JAEA-Technology-2018-006-appendix(CD-ROM).zip:29.19MB

The Horonobe URL Project has being pursued by JAEA to enhance the reliability of relevant disposal technologies through investigations of the deep geological environment within the host sedimentary formation at Horonobe, Hokkaido. The URL Project proceeds in 3 overlapping phases, "Phase I: Surface-based investigations", "Phase II: Investigations during tunnel excavation" and "Phase III: Investigations in the underground facilities", over a period of around 20 years. The OP corrosion test was prepared from 2013 FY at Niche No.3, and heating by electric heater in simulated overpack started in November, 2014. The objective of the test is acquiring data concerned with corrosion of carbon steel OP. These data will be used in order to confirm the performance of engineered barrier system. In the OP corrosion test, the diameter of simulated OP and buffer material are 100 mm and 300 mm, respectively. Concrete support using low alkaline cement was used in order to investigate the effect of cementitious materials to OP corrosion behavior. We will measure corrosion potential of carbon steel, natural potential, pH in buffer material for several years. In this report, we describe how to make simulated OP and buffer material blocks, and set sensors, and so on.

JAEA Reports

A Study of the evaluation of the excavation damaged zone in the Horonobe Underground Research Laboratory, 1; Investigation in the 140 m gallery (Joint research)

Sugita, Yutaka; Aoyagi, Kazuhei; Kubota, Kenji*; Nakata, Eiji*; Oyama, Takahiro*

JAEA-Research 2018-002, 72 Pages, 2018/06

JAEA-Research-2018-002.pdf:6.16MB

In a excavation of shafts and galleries in the deep underground for disposing radioactive waste, an excavation damaged zone (EDZ) is developed around the galleries and shafts owing to the stress redistribution. Since the characteristic changes of the rock mass in the EDZ affects the radionuclides migration behavior, it is important to understand the long-term behavior of the EDZ. Thus, we performed the in situ experiment to investigate the long-term behavior of EDZ as part of the collaborative research between Japan Atomic Energy Agency and Central Research Institute of Electric Power Industry in the 140m gallery in the Horonobe Underground Research Laboratory. In this research, we investigated the extent, mechanism of the change of hydro-mechanical characteristic, and long-term behavior of the EDZ on the basis of the comprehensive estimation of the results of the observation of the drift wall and the various investigations using boreholes such as geological investigation, the seismic and resistivity tomography, hydraulic test, water content monitoring, borehole loading test, convergence measurement, and so on. In addition, we clarified applicability and future tasks of the testing method used in this research for the investigation of the long-term behavior of the EDZ.

Journal Articles

Status of rock dynamics study in Horonobe Underground Research Laboratory, Japan

Sato, Toshinori; Aoyagi, Kazuhei; Matsuzaki, Yoshiteru; Miyara, Nobukatsu; Miyakawa, Kazuya

Rock Dynamics; Experiments, Theories and Applications, p.575 - 580, 2018/06

Rock dynamics is one of key issue for research and development of techniques for safe geological disposal of high-level radioactive waste. Horonobe Underground Research Laboratory (URL) is off-site URL constructed in soft sedimentary rock to the depth of 350m with three shafts and three level experimental galleries. Earthquake-resistant design of underground openings, observation of seismic records and groundwater pressure change due to earthquakes, and excavation disturbed zone experiment have been performed relating to the study of rock dynamics in URL project. This paper shows current status of Horonobe URL project and results of earthquake-resistant design of shafts, observation of seismic records and groundwater pressure change due to the 2011 off the Pacific coast of Tohoku Earthquake.

Journal Articles

Characterization of mineralogical controls on ammonium concentrations in deep groundwaters of the Horonobe area, Hokkaido

Sasamoto, Hiroshi; Sato, Hisao*; Arthur, R. C.*

Journal of Geochemical Exploration, 188, p.318 - 325, 2018/05

 Times Cited Count:0 Percentile:100(Geochemistry & Geophysics)

Ammonium is potentially an important constituent of deep groundwater under reducing condition. The retention of cesium by sorption in geological formations may have an important role ensuring the long-term safety of high-level radioactive waste. Cesium sorption will be affected by competing effects due to dissolve cation likely ammonium in groundwater, however. In the present study, a possible reaction to control of ammonium in deep groundwater was evaluated based on the data selected in the Horonobe as a test case in Japan. Results of investigation of mineralogy, thermodynamic evaluation of groundwaters and the Electron Probe Micro Analysis (EPMA) to identify nitrogen distribution on minerals suggest that the clay minerals bearing potassium, particularly smectite, illite and interstratified illite/smectite, appear to control the ammonium concentration in groundwaters by ion exchange reactions. Additionally, the selected groundwaters in the Horonobe seem to resemble to the gas and oil fields groundwater in the screened dataset in Japan in terms of ammonium distribution.

JAEA Reports

Records of physico-chemical parameters by geochemical monitoring system in the Horonobe Underground Research Laboratory

Mezawa, Tetsuya; Mochizuki, Akihito; Miyakawa, Kazuya; Sasamoto, Hiroshi

JAEA-Data/Code 2018-001, 55 Pages, 2018/03

JAEA-Data-Code-2018-001.pdf:10.63MB
JAEA-Data-Code-2018-001-appendix(CD-ROM).zip:8.57MB

Japan Atomic Energy Agency has been conducting "geoscientific study" and "research and development on geological disposal" in the Horonobe Underground Research Laboratory (URL) for safe geological disposal of high-level radioactive waste. Geochemical parameters of groundwater pressure, pH, and oxidation-reduction potential in the deep groundwater has been continuously monitored with monitoring systems which were developed in the Horonobe URL Project. This report presents the physico-chemical parameters of groundwater which have been obtained by the monitoring systems installed at the 140 m, 250 m and 350 m gallery. The data obtained until March 31, 2017 was summarized along with related information such as the specifications of boreholes and the excavation of the URL.

JAEA Reports

The In-situ experiment for performance confirmation of engineered barrier system at Horonobe Underground Research Laboratory; Consideration of concrete-type plug composition

Nakayama, Masashi; Niunoya, Sumio*; Miura, Norihiko*; Takeda, Nobufumi*

JAEA-Research 2017-016, 62 Pages, 2018/01

JAEA-Research-2017-016.pdf:19.99MB

The Horonobe URL Project has being pursued by JAEA to enhance the reliability of relevant disposal technologies through investigations of the deep geological environment within the host sedimentary formation at Horonobe, Hokkaido. The URL Project consists of 2 major research areas, "Geoscientific Research" and "Research and Development on Geological Disposal Technologies", and proceeds in 3 overlapping phases, over a period of around 20 years. Phase III (Investigations in the underground facilities) investigation was started in 2010 FY. The in-situ experiment for performance confirmation of engineered barrier system (EBS experiment) had started 2013 at GL-350 m gallery, and heating by electric heater in simulated overpack had started in January, 2015. One of objectives of the EBS experiment is acquiring data concerned with THMC coupled behavior. These data will be used in order to confirm the performance of engineered barrier system. This report shows consideration of concrete-type plug composition. The low alkaline cement developed by JAEA, called HFSC, was used for the plug. HFSC has used in construction test at the gallery as shotcrete in Horonobe URL.

JAEA Reports

Visualization of fractures in an Excavation Damaged Zone in the Horonobe Underground Research Laboratory (Joint research)

Aoyagi, Kazuhei; Chen, Y.*; Sakurai, Akitaka; Ishii, Eiichi; Ishida, Tsuyoshi*

JAEA-Research 2017-014, 49 Pages, 2018/01

JAEA-Research-2017-014.pdf:16.29MB

In this research, we performed the resin injection experiment at the 350 m gallery of the Horonobe Underground Research Laboratory in order to identify the three dimensional distribution of fractures induced around the gallery owing to excavation. To this end, the low viscosity resin mixed with a fluorescent substance was developed and applied to the in situ resin injection experiment. As a result, the resin was successfully penetrated into the fractures around the gallery without disturbing their situation and then fixed within them. After the experiment, the rock cores around the injection borehole were drilled for the observation. The observation under ultraviolet light revealed that the extent of the development of fractures was about 0.9 m into the borehole wall. In addition, the aperture of the fractures distributed within 0.3 m from the gallery wall was ranged 1 to 2 mm, and that distributed from 0.3 to 0.9 m was less than 1 mm. On the other hand, in the borehole televiewer (BTV) survey, only one fracture within 0.2 m from the wall could be detected owing to the resolution of the survey system. Thus, it is expected that the BTV survey underestimate the extent of the development of fractures.

Journal Articles

Analytical study on the Excavation Damaged Zone in the 350 m gallery at the Horonobe Underground Research Laboratory

Aoyagi, Kazuhei; Ishii, Eiichi

Shigen, Sozai Koenshu (Internet), 4(2), 7 Pages, 2017/09

no abstracts in English

Journal Articles

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.

47 (Records 1-20 displayed on this page)