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JAEA Reports

Study on crystalline rock aiming at evaluation method of long-term behavior of rock mass, 2 (Joint research)

Fukui, Katsunori*; Hashiba, Kimihiro*; Matsui, Hiroya

JAEA-Research 2018-006, 57 Pages, 2018/10

JAEA-Research-2018-006.pdf:2.99MB

It is important to evaluate the stability of a repository for high-level radioactive waste not only during the design, construction and operation phases, but also during the post-closure period, for time frames likely exceeding several millennia or longer. The rock mass around the tunnels could be deformed through time in response to time dependent behavior. In view of above points, this study has been started as a collaboration study with the University of Tokyo from FY2016. In the FY2017, the creep test of Tage tuff was continuously conducted and reached its twentieth year. The overview of the test was described, and the phenomenological aspects and the mechanisms of the creep of tuff were discussed with comparing the long- and short-term creep tests. The effects of loading rate and water content on rock strength were examined under various water conditions. The variable-compliance-type constitutive model was modified to reproduce those under uniaxial tension.

JAEA Reports

Study on crystalline rock aiming at evaluation method of long-term behavior of rock mass (Joint research)

Fukui, Katsunori*; Hashiba, Kimihiro*; Matsui, Hiroya

JAEA-Research 2017-010, 61 Pages, 2017/11

JAEA-Research-2017-010.pdf:16.86MB

JAEA has started this study as a collaboration study with Tokyo University from 2016. In the fiscal year of 2016, creep testing on Tage tuff was continuously conducted. Existing theory of rate process and stochastic process was modified to be applied to evaluate effects of water, and then the modified theory was validated based on the results of strength and creep tests performed under dry and wet conditions. Furthermore, effects of water contents on stress-strain curves were examined by uniaxial compression testing under various water content conditions.

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.

JAEA Reports

Study on crystalline rock aiming at evaluation method of long-term behavior of rock mass; FY2015 (Contract research)

Fukui, Katsunori*; Hashiba, Kimihiro*; Matsui, Hiroya; Kuwabara, Kazumichi; Ozaki, Yusuke

JAEA-Research 2016-014, 52 Pages, 2016/09

JAEA-Research-2016-014.pdf:7.19MB

With respect to high-level radioactive waste disposal, knowledge of the long-term mechanical stability of shafts and galleries excavated in rock is required, not only during construction and operation but also over a period of thousands of years after closure. On the other hand, it is known that rock and the rock mass surrounding the disposal gallery shows time dependent behavior such as creep or the stress-relaxation. It becomes the issue in the stability evaluation of the disposal gallery to grasp the behavior. In order to solve this issue, we pushed forward research development. we pushed forward research development. In the fiscal year of 2015, the creep testing machine for Tage tuff was moved to the new building. The creep test was continuously conducted and the total testing time exceeded 17 years. The testing equipment and procedure were examined to investigate the deformation, failure and time-dependency of rock under wet conditions and between room temperature and 100$$^{circ}$$C. The long-term strength of rock under triaxle stress state was researched with the aid of laboratory testing results and in situ stress measurement.

JAEA Reports

Study on crystalline rock aiming at evaluation method of long-term behavior of rock mass; FY2014 (Contract research)

Fukui, Katsunori*; Hashiba, Kimihiro*; Sato, Toshinori; Kuwabara, Kazumichi; Takayama, Yusuke

JAEA-Research 2015-015, 61 Pages, 2015/11

JAEA-Research-2015-015.pdf:5.52MB

With respect to high-level radioactive waste disposal, knowledge of the long-term mechanical stability of shafts and galleries excavated in rock is required, not only during construction and operation but also over a period of thousands of years after closure. On the other hand, it is known that rock and the rock mass surrounding the disposal gallery shows time dependent behavior such as creep or the stress-relaxation. It becomes the issue in the stability evaluation of the disposal gallery to grasp the behavior. About this issue, we pushed forward research development. In the fiscal year of 2014, the creep test was continuously conducted and the total testing time exceeded 17 years. The testing equipment and procedure were examined to investigate the deformation, failure and time-dependency of rock under wet conditions and between room temperature and 100$$^{circ}$$C. The long-term strength of rock under triaxial stress state was researched with the aid of laboratory testing results and in situ stress measurement.

Journal Articles

Mechanical properties of siliceous mudstone of the Wakkanai formation

Hashiba, Kimihiro*; Fukui, Katsunori*; Sugita, Yutaka; Sanada, Masanori*

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 21(2), p.75 - 82, 2014/12

Diatomaceous earth and siliceous rock are widespread in the areas along the Sea of Japan in Hokkaido Prefecture, Akita Prefecture, Noto Peninsula and Oki Islands. To construct underground structures in the siliceous rock mass, it is essential to understand its mechanical properties. In this study, siliceous mudstone of the Wakkanai formation obtained from the deep underground in Horonobe, Hokkaido was applied to various laboratory tests; uniaxial compression test, Brazilian tension test, drying shrinkage test and the test to investigate the time dependent behavior and strength recovery. The testing results showed that water has a huge effect on the deformation and failure of the siliceous mudstone; when the specimen is air dried in room temperature, the axial shrinkage strain reashes 0.9% and the strength is twice larger than that in wet condition. It was found that the siliceous mudstone exhibits the same degree of time dependent behavior and strength recovery as other rocks such as tuff and sandstone.

JAEA Reports

Study on crystalline rock aiming at evaluation method of long-term behavior of rock mass; FY2013 (Contract research)

Fukui, Katsunori*; Hashiba, Kimihiro*; Sato, Toshinori; Sanada, Hiroyuki; Kuwabara, Kazumichi

JAEA-Research 2014-020, 50 Pages, 2014/11

JAEA-Research-2014-020.pdf:2.8MB

On the radioactive waste disposal, the long-term mechanical stability of shafts and galleries excavated in rock is required. Therefore, it is very important to understand the time-dependent behavior of rock mass for evaluating long-term mechanical stability. The purpose of this study is determining the mechanisms of time-dependent behavior of rock mass by precise testing, observation and measurement in order to develop methods for evaluating long-term mechanical stability of a rock mass. This report describes the results of the activities in fiscal year 2013. In Chapter 1, we described the overview and background of this study. In Chapter 2, the results of a long-term creep test on Tage tuff, started in fiscal year 1997 are described. In Chapter 3, the result of organization and analysis for time-dependent behavior of crystalline rock was described. In Chapter 4, for the drafting of in-situ test plan, examination of the numerical analysis technique of rock mass was carried out.

JAEA Reports

Study on crystalline rock for evaluating method of long-term behavior; FY2012 (Contract research)

Fukui, Katsunori*; Hashiba, Kimihiro*; Tanno, Takeo; Hikima, Ryoichi; Sanada, Hiroyuki; Sato, Toshinori

JAEA-Research 2013-031, 52 Pages, 2013/12

JAEA-Research-2013-031.pdf:4.06MB

It is very important to understand the time-dependent behavior of rock for evaluating long-term mechanical stability. The purpose of this study is determining the mechanisms of time-dependent behavior of rock by the precise test, observation and measurement, to develop methods for evaluating long-term mechanical stability. This report describes the results of the activities in fiscal year 2012. In Chapter 1, we provide an overview and the background to this study. In Chapter 2, the results of a long-term creep test on Tage tuff, started in fiscal year 1997 are described. In Chapter 3, the experimental results concerning the loading-rate dependency of strength were examined to understand the time-dependency of rock. In Chapter 4, the stability of tunnels, around which rock stress is larger than that around a circular tunnel, were examined to obtain useful information on the future plan for ${it in-situ}$ tests in the underground research laboratory.

Journal Articles

Strength and impermeability recovery of siliceous mudstone from complete failure

Sugita, Yutaka; Sanada, Masanori; Fujita, Tomo; Hashiba, Kimihiro*; Fukui, Katsunori*; Okubo, Seisuke*

Dai-13-Kai Iwa No Rikigaku Kokunai Shimpojiumu Koen Rombunshu (CD-ROM), p.207 - 212, 2013/01

Radionuclide migration can be undesirably increased by weakening the mechanical properties of a rock mass in the excavated disturbed zone (EDZ) around the tunnels of a geolical disposal facility for high level radioactive waste. Laboratory testing of loading stress and loading time on failed siliceous mudstone specimens has identified the potential for the long-term recovery of the strength and impermeability of the rock mass in the EDZ.

JAEA Reports

Phenomenological study on crystalline rock for evaluating of long-term behavior (Contract research)

Okubo, Seisuke*; Fukui, Katsunori*; Hashiba, Kimihiro*; Hikima, Ryoichi; Tanno, Takeo; Sanada, Hiroyuki; Matsui, Hiroya; Sato, Toshinori

JAEA-Research 2011-040, 54 Pages, 2012/02

JAEA-Research-2011-040.pdf:2.85MB

With respect to high-level radioactive waste disposal, knowledge of the long-term mechanical stability of shafts and galleries excavated in rock are required, not only during construction and operation but also over a period of thousands of years after closure. Therefore, it is very important to understand the time-dependent behavior of rock for evaluating long-term mechanical stability. This report describes the results of the activities in FY2010. In Chapter 1, we provide an overview and the background to this study. In Chapter 2, the results of a long-term creep test on Tage tuff, started in FY1997 are described. In Chapter 3, the relation of loading-rate dependency of strength and stress dependency of creep life, the relationship of time dependency and probability distribution of strength or creep life and size effects are discussed to indicate more clearly the meaning of the value of "n" to express the degree of time dependency of the rock. In Chapter 4, failure criterions of a rock mass considering time dependency are discussed. In Chapter 5, the FEM analysis implemented with a generalized variable-compliance-type constitutive equation considering the change of "n" in confining pressure and strength distribution of rock mass carried out to clarify the long-term behavior of Toki granite is described. Finally, based on the numerical analysis, an in situ testing method is proposed.

Journal Articles

FEM Analysis of time-dependent behavior and failure process of deep shaft

Hashiba, Kimihiro; Sato, Toshinori

Journal of MMIJ, 124(3), p.205 - 212, 2008/03

Time-dependent behavior and failure process of deep vertical shaft was simulated with the aid of non-linear theological constitutive equation of rock. This simulation focused on the effect of gravity and the deformation behavior parallel to the direction of excavation, which has hardly been examined with horizontal roadway or tunnel. Simulation with the model of 1000 m deep vertical shaft was carried out, and the effect of rock properties and rock stress conditions was examined. It was found that time-dependency, ductility, Poisson's ratio of rock mass and the ratio between horizontal and vertical rock stresses had an effect on failure process around the bottom of vertical shaft.

Journal Articles

Recent studies on time-dependent behavior of rock and the effects of confining pressure

Hashiba, Kimihiro

Journal of MMIJ, 123(1), p.10 - 16, 2007/01

To estimate the long-term stability of deep underground structures, it is important to investigate the time-dependent behavior of rock. Loading rate dependency, creep and so on has been well examined under uniaxial stress state. However, a little knowledge has been stored up under confining pressure. In this study, recent experimental and theoretical studies on the time-dependency of rock were reviewed especially focusing on the effects of the confining pressure. Firstly, the time-dependent behavior under confining pressure was compared with that under uniaxial stress state. The loading rate dependency, creep and the relation between them were examined with the aid of the recent theoretical studies. The close relations among the time-dependency, probability distribution of rock properties and scale effect were explained theoretically. Then, the equipment and the practical testing methods to investigate the time-dependent behavior under confining pressure were reviewed.

Oral presentation

Effect of stress history on creep behavior of rock

Hashiba, Kimihiro; Matsui, Hiroya; Sato, Toshinori; Seno, Yasuhiro

no journal, , 

In this study, multi-stage creep tests were conducted with tuff and siliceous rock. The creep stresses of each stage and the duration of the first stage were variable, and the effect of the stress history on creep behavior was examined. It was found that the primary creep strain rate might be decreased by the stress history. In particular, the effect of the stress history was notable after the first stage with the large creep stress and the long duration. It was also found that the effect of the stress history of siliceous rock was larger than that of tuff.

Oral presentation

Measurement and analysis of rock mass around the shaft in Tono Mine and Mizunami Underground Research Laboratory

Hashiba, Kimihiro; Sato, Toshinori; Nakama, Shigeo

no journal, , 

no abstracts in English

Oral presentation

Variation in mechanical properties of Toki granite

Hashiba, Kimihiro; Nakama, Shigeo; Yamada, Atsuo; Sato, Toshinori

no journal, , 

no abstracts in English

Oral presentation

Deformation behavior of rock mass around a shaft for about 10 years

Hashiba, Kimihiro; Nakama, Shigeo; Sato, Toshinori

no journal, , 

no abstracts in English

Oral presentation

Multistage creep test with two types of sedimentary rock and estimation of long-term creep behavior

Hashiba, Kimihiro; Matsui, Hiroya; Seno, Yasuhiro; Sato, Toshinori

no journal, , 

no abstracts in English

Oral presentation

Study of variation in mechanical properties of Toki granite

Hashiba, Kimihiro

no journal, , 

no abstracts in English

Oral presentation

Effect of axial stress on time-dependent behavior of rock mass around shaft

Hashiba, Kimihiro; Sato, Toshinori; Seno, Yasuhiro

no journal, , 

no abstracts in English

Oral presentation

Study on crystalline rock aiming at evaluation method of long-term behaviour of rock mass (Joint research)

Hashiba, Kimihiro*; Fukui, Katsunori*; Matsui, Hiroya

no journal, , 

This poster summarize the results of Study on Crystalline Rock Aiming at Evaluation Method of Long-Term Behaviour of Rock Mass in FY 2016

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