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Journal Articles

Distinct element modeling for Class II behavior of rock and hydraulic fracturing

Shimizu, Hiroyuki*; Koyama, Tomofumi*; Murata, Sumihiko*; Ishida, Tsuyoshi*; Chijimatsu, Masakazu*; Fujita, Tomo; Nakama, Shigeo

International Journal of the JCRM (Internet), 7(1), p.33 - 36, 2011/09

In this research, newly developed numerical approaches using the Distinct Element Method (DEM) were presented, and a series of DEM simulations were performed for better understanding the physical phenomena and mechanism for the following two fundamental issues in rock engineering field. The first issue is the Class II behavior of the brittle rocks under uniaxial compression. The radial strain control method for uniaxial compression tests was introduced in the DEM codes and the Class II behavior of rocks was simulated. The simulation results suggest that the DEM can reproduce the Class II behavior of the rock successfully and revealed that the loading condition of rocks will play an important role for the Class II behavior. The second issue is the hydraulic fracturing behavior in rocks. A series of simulations for hydraulic fracturing in rock was performed by using the flow-coupled DEM code. Simulation results clearly show that the fluid infiltration behavior depends on the fluid viscosity. The fluid infiltrates into the fracture immediately, when a low viscosity fluid is used and the fluid infiltrates slowly into the cracks after the fracture generation and propagation, when a high viscosity fluid is used. Moreover, the tensile cracks are dominantly generated in the DEM simulations as expected in the conventional theory. However, the energy released from tensile cracks becomes smaller due to the fact that the tensile strength of rock is usually smaller than the compressive one. Such a small AE events is not distinguishable from noise and hard to recognize during laboratory experiments. Therefore, in AE measurements, shear type AE events with large energy are dominantly observed.

Journal Articles

Estimation of three-dimensional stress distribution and elastic moduli in rock mass of the Tono area

Nara, Yoshitaka*; Cho, S. H.*; Yoshizaki, Takaya*; Kaneko, Katsuhiko*; Sato, Toshinori*; Nakama, Shigeo; Matsui, Hiroya

International Journal of the JCRM (Internet), 7(1), p.1 - 9, 2011/01

This study presents a back analysis based on three-dimensional finite element analysis in order to estimate the regional stress fields and the elastic moduli of a rock mass simultaneously from in situ measurements. In order to improve the accuracy of the estimation of three-dimensional stress field, heterogeneities in a rock mass consisting of geological layers with different elastic properties was considered. Back analysis was applied to determine the regional stresses for a broad field study that includes Tono Mine, the Shobasama Site and the Mizunami Underground Research Laboratory (MIU) Construction Site.

Journal Articles

Geological disposal of high-level radioactive waste and the role of rock engineering

Sugihara, Kozo

International Journal of the JCRM (Internet), 5(1), p.19 - 24, 2009/03

JAEA and its predecessors have been conducting an extensive geoscientific research program since the 1970's in order to contribute to the formation of a firm scientific and technological basis for the geological disposal of high level radioactive waste in Japan. As a part of this program, in situ experiments have been performed at the Tono Mine in soft sedimentary rocks and at the Kamaishi Mine in hard crystalline rocks. An experiment on excavation disturbance has been one of these experiments and has revealed the extent and properties of the EDZ and the applicability of available measurement methods. It is suggested that mechanical excavation and controlled excavation have reduced excavation damage of the rock mass around a drift, although some improvements in the currently available methods for measuring and simulating the EDZ are essential to understand excavation disturbance in more detail. JAEA is now promoting two underground research laboratory projects in Japan; the Mizunami Underground Research Laboratory project for crystalline rocks and the Horonobe Underground Research Laboratory project for sedimentary rocks. From a rock mechanical point of view, the major interest in these projects will be paid to failure phenomenon in deep underground, rock stress estimation at larger scales and long-term physical stability of underground structure. These projects are open for international collaboration.

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