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Journal Articles

Poroelastic coefficients for siliceous rocks distributed in the Horonobe area, Hokkaido, Japan

Miyazawa, Daisuke*; Sanada, Hiroyuki; Kiyama, Tamotsu*; Sugita, Yutaka; Ishijima, Yoji*

Journal of MMIJ, 127(3), p.132 - 138, 2011/03

https://doi.org/10.2473/journalofmmij.127.132

The geology around the Japanese coast exhibits a wide distribution of mudstones composed of fossil diatoms and silica rocks. These bedrocks are categorized as porous and low permeability rock. When underground openings at rocks with such rock mechanics properties are constructed, evaluation which takes into account flow-stress coupling behavior is required. Poroelasticity treats both pore fluids and the mineral particles which make up rocks as compressible. Consequently, its application can extend to rock that is harder than soil materials. In this study, laboratory experiments by using the siliceous rocks distributed in the Horonobe area, Hokkaido, Japan were carried out as a case study. Proposal method for obtaining poroelasic coefficients as well as determination of poroelastic coefficients distributed in the Horonobe area are described in this paper.

JAEA Reports

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.

Journal Articles

Development of Stress Measuring System by Overcoring Method Suitable for Soft Rocks

Ghimile, H. N.*; Ishijima, Yoji*; Sugawara, Takayuki*; Nakama, Shigeo

Shigen To Sozai, 119(9), 0 Pages, 2003/00

Most in-situ data on rock stresses are from hard or moderately hard rock. It is necessary to develop a stress measurement method for soft rock, toward obtaining the in-situ stress state in such rock. We developed a stress meter that measures seven components of diametrical deformation and axial deformation in a pilot borehole during overcoring and records the measurements on a small data logger installed within it. From these deformation data, three-dimensional stress states in rock are determined using the observation equation derived from the analytical elastic solution. The stress meter is inserted into a 40-mm pilot borehole that can range in water content from dry to completely wet. The advantages of this stress meter are its smallness, ease of use, reusability, ability to measure at any borehole depth, and efficiency, since very little time is required for insertion and withdrawal and no time is needed to shift from insertion to overcoring. Moreover, elastic properties of the roc

JAEA Reports

A study on the mechanical properties of Neogene sedimentary rock; A particular reference to the effect of the geological process and the elapsed time on its mechanical properties after coring

Ishijima, Yoji*

JNC TJ8400 2001-026, 45 Pages, 2001/02

JNC-TJ8400-2001-026.pdf:3.65MB

Coring of rock from the strata induces various changes in the cored sample such as change from deoxidation circumstance to oxidation, change from water saturated condition to transpiration, change from virgin rock stress state to stress relieved condition etc. In accordance to these changes, rock suffers weathering, which in tern induces change of mechanical properties. This change could advance quickly in newly deposited sedimentary rock of relatively large porosity. From standpoint of development of underground for various purpose, it is important to know the in-situ mechanical properties of rock. This information is also important to give precise evaluation of rock stresses measured based on the overcoring method. First purpose of this study is to develop a measuring method which gives precise evaluation of strength and deformability of in-situ rock. For this, a measuring system has been developed to conduct the uniaxial compression test, in the field, by using light-weight loading apparatus for the specimen quickly prepared from the core. It has been proved that the test can be completed in less than 1 hour after the core is obtained. It has also been cleared that the values such as Young's modulus, compressive strength and tensile strength evaluated by the newly developed system are almost same as those obtained in the laboratory by using the servo-controlled testing machine. Second purpose of this study is to test two different methods to preserve the core: one is to wrap the grease-coated core by the polyethylene film and another is to keep the core in submerged condition. Compression tests have been conducted four times during three months. Neither the change of strength with elapsed time nor the difference of strength between the two storing conditions has been detected. This could be attributed to the fact that the sandstone that is used receives little weathering effect. Third purpose of this study is to investigate the influence of the geological ...

JAEA Reports