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Nara, Yoshitaka*; Kato, Masaji*; Sato, Tsutomu*; Kono, Masanori*; Sato, Toshinori
Proceedings of 5th ISRM Young Scholars' Symposium on Rock Mechanics and International Symposium on Rock Engineering for Innovative Future (YSRM 2019 and REIF 2019) (USB Flash Drive), 6 Pages, 2019/12
It is important to understand the long-term migration of radionuclides considering carious rock engineering projects such as the geological disposal of radioactive wastes. The network of fractures and pores in a rock mass can play important roles as the pathway of the fluid flow of rock. Usually groundwater contains fine-grained minerals such as clays. It is probable that the accumulation of the fine-grained minerals occurs in a fracture if the groundwater flows in a fracture in a rock. In this study, we have conducted the permeability measurement using water including clays. Specifically, we used a macro-fractured granite as a rock sample, and investigated the change of the permeability under the flow of the water including clays. It was shown that the hydraulic conductivity decreased with elapsed time.
Aoyagi, Kazuhei; Chen, Y.*; Ishii, Eiichi; Sakurai, Akitaka; Ishida, Tsuyoshi*
Proceedings of 5th ISRM Young Scholars' Symposium on Rock Mechanics and International Symposium on Rock Engineering for Innovative Future (YSRM 2019 and REIF 2019) (USB Flash Drive), 6 Pages, 2019/12
In the excavation of a repository for high-level radioactive waste (HLW) disposal, it is important to understand the hydro-mechanical characteristics of the Excavation Damaged Zone (EDZ) induced around the gallery because EDZ can lead to the migration pathway of radionuclides. Thus, we performed the resin injection experiment at the 350 m gallery of Horonobe Underground Research Laboratory in Japan to investigate the characteristics of fractures induced around the gallery wall in excavation. In the experiment, we developed a low viscosity resin mixed with a fluorescent substance and injected to the borehole drilled about 1 m in length. After the experiment, we overcored around the injection borehole. The observation on the cut surface of the overcore under ultraviolet light revealed that the fractures were distributed within 0.8 m from the gallery wall. Fractures are interconnected each other in particular within 0.25 m from the niche wall. Furthermore, fractures with large aperture (about 1.0 mm) were developed in that region. These observed results will be fundamental information for understanding of the fracturing process in the EDZ.
Okazaki, Yasuyuki*; Hayashi, Hisashi*; Aoyagi, Kazuhei; Morimoto, Shingo*; Shinji, Masato*
Proceedings of 5th ISRM Young Scholars' Symposium on Rock Mechanics and International Symposium on Rock Engineering for Innovative Future (YSRM 2019 and REIF 2019) (USB Flash Drive), 6 Pages, 2019/12
In the design of tunnel support, the behavior of the rock mass around a tunnel and the stress acting on the tunnel support may be predicted using a numerical analysis. However, in such a numerical analysis, it is common to assume that each stratum comprises a homogeneous material, ignoring the heterogeneity of the geomechanical properties inherent to the rock mass. For this reason, it is not unusual for the results of the numerical analysis to differ from the actual behavior. We performed a tunnel excavation analysis considering the heterogeneity of the geomechanical properties in the rock mass to investigate the local increase in the tunnel support stress obtained in the 350 m gallery at the Horonobe Underground Research Laboratory. The results revealed that, in order to predict the locally increased support stress in advance, it is necessary to carry out a tunneling excavation analysis considering the heterogeneity of the geomechanical properties. It was also revealed that the scale at which the geomechanical properties fluctuate is an important factor.
Miyakawa, Kazuya; Aoyagi, Kazuhei; Sasamoto, Hiroshi; Akaki, Toshifumi*; Yamamoto, Hajime*
Proceedings of 5th ISRM Young Scholars' Symposium on Rock Mechanics and International Symposium on Rock Engineering for Innovative Future (YSRM 2019 and REIF 2019) (USB Flash Drive), 6 Pages, 2019/12
The construction and operation of geological repositories require excavation and ventilation of galleries, with significant groundwater drainage. Desaturation of rock around galleries is unavoidable and may affect hydraulic properties and redox conditions. This study used numerical modeling to assess the influence of dissolved gas on the degree of saturation of rock surrounding excavated galleries, focusing on siliceous mudstone rock in the 140 m, 250 m, and 350-m-deep galleries of the Horonobe Underground Research Laboratory, Japan. Based on previous 
electrical survey, the degree of saturation in the 250 m gallery was higher than that in the 140 m and 350 m galleries. In the Horonobe area, deep groundwater contains high concentrations of dissolved methane, and exsolution of this methane from pore water can affect desaturation. Simple numerical modeling, including simulation of multiphase flows, was undertaken for each gallery to confirm the effect of dissolved gas and rock permeability on desaturation. A sensitivity analysis was performed by varying dissolved gas contents and permeability. Results indicate that the dissolved gas content affects both the degree of saturation and its spatial extent, whereas rock permeability affects only the latter. Higher dissolved gas concentrations result in lower degrees of saturation with a greater spatial extent of desaturation, and higher permeability leads to greater extents of desaturation. It is therefore likely that gas content, rather than rock permeability, caused the observed variations in the saturation degree.
Ozaki, Yusuke; Matsui, Hiroya; Kohashi, Akio; Onoe, Hironori
no journal, ,
In this study, we introduce the hydro-mechanical behavior observed in the fracture granite medium. The rock deformation due to the change in hydraulic pressure according to the borehole drilling was observed at the 500m stage in Mizunami underground research laboratory. The observed data of rock deformation shows the elastic behavior although the several fractures are observed in the monitoring borehole. We conduct a numerical simulation for the evaluation of this behavior by using finite element methods. The magnitude of simulated deformation is similar value with the observed data. From these results, we conclude that the movement of fracture joints is slight and the subsurface facility is stable to the change in hydraulic response.