International Journal of Rock Mechanics and Mining Sciences, 159, p.105229_1 - 105229_17, 2022/11
In an underground repository for high-level radioactive waste disposal, fracture transmissivity in an excavation damaged zone (EDZ) along tunnels or deposition holes can decrease during the post-closure period via processes such as self-sealing by clay-swelling at the EDZ's fracture surface or an increase in effective normal stress acting on the fractures owing to swelling of backfilling or buffer materials. Hydromechanical coupling models for the stress-dependence of fracture transmissivity are helpful to estimate the change in an EDZ's fracture transmissivity after closure. The applicability of the applied models should be confirmed by in situ tests at the given site; this appears to be facilitated by using constant-head step injection tests. However, injection testing is rarely applied to EDZ fractures. To investigate the applicability of injection tests, the present study performed them on single, tensile EDZ fractures in the Horonobe Underground Research Laboratory hosted by poorly swelling mudstone. Furthermore, the Barton-Bandis normal stress-dependent fracture-closure model quantified the stress-dependence of EDZ facture transmissivity. The fracture's hydraulic aperture increased gradually during injection, and its variation was well reproduced by fitting the model. Although the model requires the normal stress, this parameter was reasonably estimated by the fitting analyses. Constant-head step injection tests coupled with the Barton-Bandis model is believed to be a convenient method for preliminarily quantifying or verifying the stress dependence of EDZ fracture transmissivity, at least for poorly self-sealed, tensile EDZ-fractures.
Onoe, Hironori; Ishibashi, Masayuki*; Ozaki, Yusuke; Iwatsuki, Teruki
International Journal of Rock Mechanics and Mining Sciences, 144, p.104737_1 - 104737_14, 2021/08
In this study, we investigated the methodology of modeling for fractured granite around the drift at a depth of 500 m in the Mizunami Underground Laboratory, Japan as a case study. As a result, we developed the fracture modeling method to estimate not only geological parameters of fractures but also hydraulic parameters based on the reproducibility of trace length distribution of fractures. By applying this modeling method, it was possible to construct a Discrete Fracture Network (DFN) model that can accurately reproduce the statistical characteristics of fractures.
Gens, A.*; Alcoverro, J.*; Blaheta, R.*; Hasal, M.*; Michalec, Z.*; Takayama, Yusuke; Lee, C.*; Lee, J.*; Kim, G. Y.*; Kuo, C.-W.*; et al.
International Journal of Rock Mechanics and Mining Sciences, 137, p.104572_1 - 104572_19, 2021/01
Bentonite-based engineered barriers are a key component of many repository designs for the confinement of high-level radioactive waste and spent fuel. Given the complexity and interaction of the phenomena affecting the barrier, coupled hydro-mechanical (HM) and thermo-hydro-mechanical (THM) numerical analyses are a potentially useful tool for a better understanding of their behaviour. In this context, a Task (INBEB) was undertaken to study, using numerical analyses, the hydro-mechanical and thermohydro-mechanical Interactions in Bentonite Engineered Barriers within the international cooperative project DECOVALEX 2019. Two large scale tests, largely complementary, were selected for modelling: EB and FEBEX. The EB experiment was carried out under isothermal conditions and artificial hydration and it was dismantled after 10.7 years. The FEBEX test was a temperature-controlled non-isothermal test combined with natural hydration that underwent two dismantling operations, a partial one after 5 years of heating and a final one after a total of 18.4 years of heating. Direct observation of the state of the barriers was possible during the dismantling operations. Four teams performed the HM and THM numerical analyses using a variety of computer codes, formulations and constitutive laws. For each experiment, the basic features of the analyses are described and the comparison between calculations and field observations are presented and discussed. Comparisons involve measurements performed during the performance of the test and data gathered during dismantling. A final evaluation of the performance of the modelling closes the paper.
International Journal of Rock Mechanics and Mining Sciences, 136, p.104538_1 - 104538_8, 2020/12
It is necessary to apply reliable numerical simulation techniques to assess the mechanical behaviour of repositories for the geological disposal of radioactive waste over a long period of time. Having a constitutive model that can describe the mechanical behaviour of bentonite is key to such numerical simulations. In this study, the applicability of linear elastic constitutive model with swelling term is examined focusing on the density heterogeneity by applying to the in situ Full-scale Engineered Barrier Experiment (FEBEX) in Grimsel. It was confirmed that this constitutive model underestimates the density change. Instead, mechanical behaviour was re-simulated by unsaturated elasto-plastic constitutive model using the changes in degree of saturation as input data. Although no feedback effects of mechanical behaviour on hydraulic and thermal behaviour were taken into account, two-dimensional stress and density could be reproduced.
International Journal of Rock Mechanics and Mining Sciences, 100, p.10 - 22, 2017/12
The highest transmissivity of fractures in a rock mass is crucial for conservative assessment of a site for radioactive waste disposal. However, it is not realistic to measure that of all possible fractures in a site. Previous studies indicated that the highest potential transmissivities of fractures in fault zones can be predicted by a rock mechanical indicator, ductility index (DI). Noting that the mechanism of formation and preservation of pore structures in fault-zone fractures may be the same as that of pore structures in discrete shear fractures. This study investigated whether or not the DI model is applicable to discrete shear fracture systems, using geological and hydrological data of discrete shear fractures in a Neogene diatomaceous mudstone (Koetoi Formation). As a result, the data set obtained by this study well fits the existing data sets of the DI model, suggesting that the DI mode is applicable to discrete shear fracture systems as well as fault zones.
Miyakawa, Kazuya; Nohara, Tsuyoshi; Tokiwa, Tetsuya; Yamazaki, Masanori*
International Journal of Rock Mechanics and Mining Sciences, 70, p.332 - 342, 2014/09
A large amount of groundwater drain induced by an excavation of an underground facility will influence parameters of site formations such as permeability. In this study, a spectral analysis was applied to long-term records of atmospheric response of pore pressure in order to obtain time history of rock permeability change at the Horonobe Underground Research Laboratory (URL) in Japan. This study revealed that the excavation of the URL has influenced aquifers around the URL, and has reduced the vertical hydraulic diffusivity in the aquifers. At the point of ca. 130 m distant away from the URL, the hydraulic diffusivity has decreased in approximately 70% after 5 years from start of excavation of the URL. At the point of ca. 860 m distant away from the URL, the vertical hydraulic diffusivity has decreased in approximately 26% even though pore pressure has not changed remarkably. These results indicate that groundwater consequently becomes difficult to flow, and then safe-side estimation with respect to geological disposal system was obtained. This study confirmed that long-term history of permeability change can be monitored by using long-period records of pore pressure and atmospheric pressure. During the development of a geological disposal system, which takes several tens of years, the vertical permeability can be monitored continuously from the start of the excavation through the post-closure of the repository.
Sanada, Hiroyuki; Hikima, Ryoichi; Tanno, Takeo; Matsui, Hiroya; Sato, Toshinori
International Journal of Rock Mechanics and Mining Sciences, 59, p.50 - 56, 2013/04
In this paper, application of DSCA to the Toki Granite in the region around the MIU is described. The purpose of this study is to confirm the reliability of DSCA in characterising crystalline rocks and to understand stress conditions around the MIU. For verification of in situ stress measurement results obtained in this study, they were compared to in situ stress measurement results from hydraulic fracturing studies and regional stresses estimated from stress indicators such as triangulation etc. in the Tono region of Central Japan. Based on the comparisons carried out in this study acquired by DSCA, the maximum principal stress direction in the MIU area was estimated to vary from N to W, which corresponded with stress indicators. Principal stress ratios decreased with depth in the region, with the exception of stresses in a fault zone.
Sanada, Hiroyuki; Nakamura, Takahiro*; Sugita, Yutaka
International Journal of Rock Mechanics and Mining Sciences, 56, p.127 - 135, 2012/12
A Mine-by Experiment was carried out to investigate the development of an EDZ in one of the deep vertical shafts excavated in Neogene sedimentary rocks at the Horonobe URL site. The objective of this experiment is to understand the deformation and failure behavior and the hydraulic properties of the EDZ developed during sinking of the deep shaft. Before and after shaft sinking, BTV, borehole expansion tests, permeability tests and seismic velocity logging were carried out to determine initial conditions and changes in the mechanical and hydraulic properties. During shaft sinking, instruments such as extensometers and stress sensors were installed in the rock mass and in the shaft lining for stress measurements around the shaft circumference and to determine rock mass response to excavation. The variation of both mechanical and hydraulic properties was largest within 1 m of the shaft wall and the variation in hydraulic conductivity was in the range of one order of magnitude.
Sanada, Hiroyuki; Sugita, Yutaka; Kashiwai, Yoshio*
International Journal of Rock Mechanics and Mining Sciences, 54, p.27 - 36, 2012/09
In this paper, application of the multi-interval displacement sensor using Fiber Bragg Grating (FBG) technology in the Horonobe URL is described. Laboratory tests were carried out to obtain the relational expression computed from the relationship of the variation in the Bragg wavelength, temperature and displacement. From the results of laboratory test, accuracy of sensor was evaluated better than 0.5% of the measurement range. In situ monitoring at the Horonobe URL using the developed sensor was carried out in parallel with nearby monitoring using a conventional extensometer, which is electrical signal system type, for verification of the developed sensor. In situ test results indicate that the displacement values from both the developed sensor and the conventional extensometer are almost equivalent. One of the advantages of the developed sensor was that there was no noise in the obtained monitoring data, while the data from the conventional extensometer shows some noise.
Tokiwa, Tetsuya; Tsusaka, Kimikazu; Ishii, Eiichi; Sanada, Hiroyuki; Tominaga, Eiji*; Hatsuyama, Yoshihiro*; Funaki, Hironori
International Journal of Rock Mechanics and Mining Sciences, 48(5), p.773 - 781, 2011/07
This paper focuses attention on stress field that produced fault system, and presents an example of the relationship between fault system and rock mass response to shaft excavation in soft sedimentary rocks in the Horonobe area, Japan. The directions determined by fault-slip analysis are close to the direction of maximum and minimum diameter reduction in the shaft. The results show that fault system can affects rock mass response to shaft excavation in soft rock and furthermore, and it is considered that the rock mass deformation was controlled by fault system. In addition, it is likely that we can assess and predict rock mass behavior by focusing on palaeo-stress field that produced fault system.
Shimizu, Hiroyuki*; Koyama, Tomofumi*; Ishida, Tsuyoshi*; Chijimatsu, Masakazu*; Fujita, Tomoo; Nakama, Shigeo
International Journal of Rock Mechanics and Mining Sciences, 47(2), p.323 - 333, 2010/02
Matsuki, Koji*; Nakama, Shigeo; Sato, Toshinori
International Journal of Rock Mechanics and Mining Sciences, 46(1), p.31 - 50, 2009/01
This paper consists of two parts. In Part I, we propose a method for determining regional stress from limited stress data by using a 3D finite element method (FEM) in which we define regional stress for a heterogeneous rock mass composed of different rock bodies and a large fault as a displacement boundary condition that is consistent with the mean trend of in situ stress. This method was applied to a small-scale heterogeneous model with a large planar fault that penetrates the region to clarify the estimation accuracy and the effects of incorrect stiffness of the fault, incomplete stress data, and the assumption that the fault shows partial, but not complete, sliding. The results showed that (1) the method proposed in this study can accurately estimate the stress distribution in the region under consideration except at the bottom when the sliding area of the fault is small, (2) the reproducibility of the given stress indicates that the method can be used to estimate appropriate values of the normal and shear stiffnesses of the fault, and (3) both incomplete stress data and the assumption that the fault does not slide decrease the accuracy of stress estimation while the given stresses are approximately reproduced. In Part II, this method is applied to the Tono area, in Japan.
Sugita, Yutaka; Rutqvist, J.*; Brgesson, L.*; Chijimatsu, Masakazu*; Nguyen, T. S.*; Jing, L.*; Noorisha, J.*; Tsang, C.-F.*
International Journal of Rock Mechanics and Mining Sciences, 38(1), p.129 - 142, 2001/00
no abstracts in English
Sugita, Yutaka; Nguyen, T. S.*; Brgesson, L.*; Chijimatsu, Masakazu*; Rutqvist, J.*; Fujita, Tomoo; Hernelind, J.*; Kobayashi, Akira*; Onishi, Yuzo*; Tanaka, Makoto*; et al.
International Journal of Rock Mechanics and Mining Sciences, 38(1), p.79 - 94, 2001/00
Chijimatsu, Masakazu*; Fujita, Tomoo; Sugita, Yutaka; Amemiya, Kiyoshi*; Kobayashi, Akira*
International Journal of Rock Mechanics and Mining Sciences, 38(1), p.67 - 78, 2001/00
Kobayashi, Akira*; Fujita, Tomoo; Chijimatsu, Masakazu*
International Journal of Rock Mechanics and Mining Sciences, 38(1), p.45 - 57, 2001/00
Sugita, Yutaka; Rutqvist, J.*; Noorisha, J.*; Tsang, C.-F.*; Brgesson, L.*; Nguyen, T. S.*
International Journal of Rock Mechanics and Mining Sciences, 38(1), p.105 - 127, 2001/00
Brgesson, L.*; Chijimatsu, Masakazu*; Fujita, Tomoo; Nguyen, T. S.*; Rutqvist, J.*; Jing, L.*
International Journal of Rock Mechanics and Mining Sciences, 38(1), p.95 - 104, 2001/00
Chen, C.*; Nishiyama, Takashi*; Kusuda, Hiromu*; Kita, H.*; Sato, Toshinori
International Journal of Rock Mechanics and Mining Sciences, 36(4), p.535 - 541, 1999/06