Influences of sedimentary history on the mechanical properties and microscopic structure change of Horonobe siliceous rocks

Sanada, Hiroyuki; Niunoya, Sumio*; Matsui, Hiroya; Fujii, Yoshiaki*

Journal of MMIJ, 125(10,11), p.521 - 529, 2009/11

This paper shows the results obtained from the laboratory tests and microscopic observation of Horonobe siliceous rocks. The consolidated undrained and drained triaxial compression tests showed different behaviors of strain-softening, pore pressure and dilatancy between diatomaceous and siliceous mudstones. Stress-strain behavior changed from strain-softening to ductile behavior under high confining pressure and pore pressure increased gradually even after peak strength for diatomaceous mudstone. Diatomaceous mudstone yielded under hydrostatic pressure of 10 MPa in isotropic consolidation test. This yielding was regarded as pore collapse based on the variation of hydraulic conductivity which was estimated from variation of volumetric strain in isotropic consolidation test, effective porosity and microscopic observation before and after the yielding.

Deformation and failure behavior of rock mass around the ventilation shaft in Horonobe URL

Sanada, Hiroyuki; Sugita, Yutaka; Fujii, Yoshiaki*

Proceedings of 3rd International Workshop and Conference on Earth Resources Technology 2009 (CD-ROM), p.149 - 158, 2009/05

EDZ is considered to be important issues in repositories since this is relevant to plug design, support design etc. As a part of the research and development on the geological isolation, JAEA has been implementing the Horonobe URL Project. Deformation and failure behavior around a shaft in URL is described in the paper. Tunnel shape are being measured by a laser displacement sensor to clarify dimension and mechanism of breakouts along the shaft wall. Displacement measurement by extensometers are being carried out to understand deformation behavior in the surrounding rock mass. Breakouts of about 50 cm deep in N-S direction are more frequently observed with excavation depth. The breakout direction was consistent with the maximum horizontal stress which was estimated to be approximately in E-W direction by hydrofracturing tests. Compressive deformation of rock mass also increased with excavation depth. Most part of the deformation occurred within 1 m from the shaft wall.

Mechanical property of Horonobe siliceous rock

Sanada, Hiroyuki; Matsui, Hiroya; Fujii, Yoshiaki*

Dai-12-Kai Iwa No Rikigaku Kokunai Shimpojiumu Koen Rombunshu (CD-ROM), p.703 - 708, 2008/09

This paper shows the result of rock mechanical investigations which have been carried out as a part of the investigations of Horonobe Underground Research Project. The results of the investigations are summarized as follows. Uniaxial compression and tensile strength of siliceous rock distributed in Wakkanai formation is larger than diatomaceous mudstone distributed in Koetoi formation. Stress-strain curve shows strain softening behavior from results of tri-axial compression test. Pore pressure and dilatancy behavior show different trends as compared with diatomaceous mudstone and siliceous rock.

Development of a system to measure the in-situ mechanical conditions and to evaluate easiness of underground construction in the weak sedimentary rock

Ishijima, Yoji*; Fujii, Yoshiaki*; Kawakita, Minoru*; Nakama, Shigeo; Matsui, Hiroya

JNC TY7400 2004-002, 91 Pages, 2003/03

JNC-TY7400-2004-002.pdf:3.33MB

The ratio of soft rock occupied in the whole rock mass in Japan is relatively high. Strata control problems occur more frequently in soft rock than in hard rock, since fracture and large deformation are easily induced in soft rock whose strength and stiffness are small in magnitude. A rational method to overcome these problems is to develop such system to measure the rock stresses as well as to evaluate the in-situ strength of the rock mass and to use these data to predict the phenomena occurred during nderground constructions and to reflect them to design of the rock mass structure. However, the technique of measurements which can be used in soft rock has not been developed to this day, due to many problems to overcome. Purpose of the present investigation is to develop a system to measure such components as the rock stress, the width of the fissured one and the creep deformation, by using a single borehole drilled in the soft rock. To confirm the validity of this system, the in-situ measurements were conducted in the soft iatomaceous mudstone in Horonobe district, Hokkaido, Japan. Various findings obtained in this investigation will be reported.

Applicability of low alkalinity cement for construction and alteration of bentonite in the cement

Iriya, Keishiro*; *; Kubo, Hiroshi*; Uegaki, Yoshiaki*

JNC TJ8400 2002-038, 83 Pages, 2002/02

JNC-TJ8400-2002-038.pdf:24.9MB

A concept of radioactive waste repository in which both bentonite and cementitious materials exist in deep cavern as engineered barriers is proposed. It is pointed out that pore water of cement is approximately 12.0 to 13.0 of pH and that it maintains for a long period. Therefore alteration of bentonite and rocks should be studied. Mixing test upon some interaction between modeled cement water and bentonite and rocks have been carried out since 1995 as a part of TRU repository's study. And low alkalinity of cement has been studied as parallel to study on alteration of bentnite. HFSC which has high fly ash content and which shows approximately 10.5 to 11.0 of pH of pore water was developed. Cementitious materials are generally use as a combination with steel, since its tensile strength is low. The corrosion of steel in concrete becomes a big problem in case of decreasing pH of cement. There is little available reference, since low alkalinity cement is quite new and special ordered one. Accelerating test for corrosion in low alkalinity concrete were carried out in order to collect data of corrosion. Although alteration of bentonite by several types of modeled cement water was tested. Long term test by actual cement pore water has not carried out. The alteration in 360 days was investigated. Conclusion obtained in this study is following. [Corrosion of steel (re-bar)] (1)Re-bar in HFSC with 60% of W/C is signmcantly corroded. The corrosion rate is bigger than the rate of ordinary used cement. (2)Diffusivity of Cl ion in HFSC is similar to it in OPC comparing by the same water powder ratio. (3)Corrosion rate of HFSC 30 is similar to OPC60. However corrosion is progressed in HFSC 30 without Cl ion due to lower alkalinity, but it isn't done in OPC within a certain amount of Cl ion. [Alteration of bentonite and rocks] (1)Although no secondary minerals was observed in HFSC, monmorironite is gradually lost by increasing calcite. (2)Secondary ...

Initial stress measurement of Horonobe Siliceous rocks by DSCA method

Yamaguchi, Masaki*; Fujii, Yoshiaki*; Fukuda, Kazuhiro*; Matsui, Hiroya

no journal, , 

no abstracts in English

Isotropic compression test of neocene diatomaceous rocks distributed in Horonobe area

Sanada, Hiroyuki; Yamaguchi, Masaki*; Fujii, Yoshiaki*; Fukuda, Kazuhiro*; Matsui, Hiroya

no journal, , 

no abstracts in English

Rock stress measurement by borehole deformation method to siliceous mudstone; A Measurement case of 250 m depth drift at the Horonobe Underground Research Laboratory

Kumakura, Satoshi*; Sugita, Yutaka; Sanada, Hiroyuki; Nakamura, Takahiro; Obara, Yuichi*; Sugawara, Takayuki*; Fujii, Yoshiaki*

no journal, , 

no abstracts in English