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Nara, Yoshitaka*; Kato, Masaji*; Sato, Tsutomu*; Kono, Masanori*; Sato, Toshinori
Journal of MMIJ, 138(4), p.44 - 50, 2022/04
It is important to understand the long-term migration of radionuclides when considering rock engineering projects such as the geological disposal of radioactive waste. The network of fractures and pores in a rock mass plays a major role in fluid migration as it provides a pathway for fluid flow. The geometry of a network can change due to fracture sealing by some fine-grained materials over long-term periods. In the present study, we use a macro-fractured granite sample to investigate the change of permeability that occurs under the flow of water that includes two different amounts of clay. Findings showed that clay accumulated in a fracture and that the permeability (hydraulic conductivity) of the granite sample decreased over time, which was greater in for the higher clay content. We concluded that the accumulation of clay minerals in the fracture decreased the permeability of the rock. Furthermore, we consider that the filling and closure of fractures in rock is possible under the flow of groundwater that includes clay minerals.
Matsukawa, Shun*; Itakura, Kenichi*; Hayano, Akira; Suzuki, Yukinori*
Journal of MMIJ, 133(11), p.256 - 263, 2017/11
LIDAR detects a rock mass surface configurations as a point cloud. DiAna (Discontinuity Analysis) is a Matlab tool which was developed for geo-structural analysis of rock mass discontinuities. DiAna segments a point cloud into bounding boxes to estimate the surface of a rock mass. However, an expert's skills necessary to determine the appropriate size of the bounding boxes for DiAna. We developed the VBS (Variable-Box Segmentation) algorithm to determine the appropriate box size depending on the location of the point cloud and to estimate the surface of a rock mass. The performance of the VBS algorithms was evaluated by comparison with the DiAna algorithm. The results of comparison showed that the VBS algorithm estimated planes more accurately for the reference planes than the DiAna algorithm. Therefore, the VBS algorithm determines appropriate box sizes automatically depending on the location of the point cloud and estimates the surface appropriately.
Hayano, Akira; Itakura, Kenichi*
Journal of MMIJ, 133(4), p.76 - 86, 2017/04
no abstracts in English
Aoyagi, Kazuhei; Ishii, Eiichi; Ishida, Tsuyoshi*
Journal of MMIJ, 133(2), p.25 - 33, 2017/02
In the construction of a deep underground facility, the hydromechanical properties of the rock mass around an underground opening are changed significantly due to stress redistribution. This zone is called an excavation damaged zone (EDZ). In high-level radioactive waste disposal, EDZs can provide a shortcut for the escape of radionuclides to the surface environment. Therefore, it is important to develop a method for predicting the detailed characteristics of EDZs. For prediction of the EDZ in the Horonobe Underground Research Laboratory of Japan, we conducted borehole televiewer surveys, rock core analyses, and repeated hydraulic conductivity measurements. We observed that niche excavation resulted in the formation of extension fractures within 0.2 to 1.0 m into the niche wall, i.e., the extent of the EDZ is within 0.2 to 1.0 m into the niche wall. These results are largely consistent with the results of a finite element analysis implemented with the failure criteria considering failure mode. The hydraulic conductivity in the EDZ was increased by 3 to 5 orders of magnitude compared with the outer zone. The hydraulic conductivity in and around the EDZ has not changed significantly in the two years following excavation of the niche. These results show that short-term unloading due to excavation of the niche created a highly permeable EDZ.
Nagayasu, Takaaki; Torikai, Kazuyoshi; Ohara, Yoshiyuki; Uechi, Yasufumi
Journal of MMIJ, 131(6), p.357 - 358, 2015/06
no abstracts in English
Sakao, Ryota; Saito, Hiroshi; Torikai, Kazuyoshi; Taki, Tomihiro
Journal of MMIJ, 130(6), p.275 - 278, 2014/06
Ningyo-toge Environmental Engineering Center, Japan Atomic Energy Agency has been managing the Ningyo-toge Uranium Mine and Togo Uranium Mine in accordance with the Mine Safety laws. This paper shows a summary of the remediation activities of Mill Tailings Pond including the strategy and monitoring.
Sukenaga, Sohei*; Osugi, Takeshi; Inatomi, Yosuke*; Saito, Noritaka*; Nakashima, Kunihiko*
Journal of MMIJ, 129(5), p.203 - 207, 2013/05
Viscosity changes of RO-SiO
-FexO (R = Ca, Sr, Ba) melts due to changes in the oxidation states of the iron ions by systematically varying the oxygen partial pressure were measured at 1773 K. The initial compositions of the samples were 30RO-60SiO-10FeO
(mol%), and the ratio of Fe
toFe
in the RO-SiO-FexO melts increased with increasing oxygen partial pressure in all samples. Meanwhile, the viscosity of all the RO-SiO-FexO melts decreased with increasing Fe to total-Fe ratio (Fe/t-Fe). The data indicate that the increase in the amount of Fe ions, which behave as network modifiers, would result in depolymerization of the silicate anions. In addition, the viscosity of the melts increased in the order of alkaline-earth cationic radius (Ba 
Sr Ca) when the Fe/t-Fe values of the melts were comparable. This would be due to the change in the coordination structure of Fe in the melts.
Sato, Toshinori; Tanno, Takeo; Hikima, Ryoichi; Sanada, Hiroyuki; Kato, Harumi*
Journal of MMIJ, 129(2,3), p.59 - 64, 2013/02
Japan Atomic Energy Agency has been conducting 
stress measurements by overcoring method, to aiming establish a firm scientific basis for safe geological disposal. Core disking is observed where rock stress measurements are performed by compact conical-ended borehole overcoring technique in the depth of 300 m from the surface at the Mizunami Underground Research Laboratory. In this report, failure initiation of core disking is discussed.
Tamamura, Shuji*; Endo, Ryo*; Shimizu, Satoru*; Iwatsuki, Teruki; Amano, Yuki; Omi, Yasushi*; Igarashi, Toshifumi*
Journal of MMIJ, 128(10,11), p.570 - 575, 2012/10
no abstracts in English
Sato, Toshinori; Tanno, Takeo; Hikima, Ryoichi; Sanada, Hiroyuki; Kato, Harumi*
Journal of MMIJ, 128(7), p.449 - 454, 2012/07
Hydraulic fracturing has provided many determinations of in situ stress, but also include many errors in data obtained, as the ISRM suggested. This report provides a comparison of the data obtained by the conventional hydraulic fracturing method with those of a new high-compliance system. Analysis of the results of 57 hydraulic fracturing tests in granite to a maximum depth of 1000m, indicated that 35% of the data obtained using the conventional system is low quality. In addition, the maximum horizontal stresses calculated using the conventional equation is overestimated by about 23%. In contrast, the data obtained with the new system is better quality compared with the conventional system, because flow rate of pressurization is measured in the borehole near the test section rather than at surface, thus reducing compliance in the system and the inherent errors introduced in the stress calculations.
Miyazawa, Daisuke*; Sanada, Hiroyuki; Kiyama, Tamotsu*; Sugita, Yutaka; Ishijima, Yoji*
Journal of MMIJ, 127(3), p.132 - 138, 2011/03
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.
Amamoto, Ippei
Journal of MMIJ, 127(1), p.1 - 7, 2011/01
The pyroprocess as a non-aqueous reprocessing, is oriented as a complementary concept for the Fact Project. The pyroprocess possesses some inherent problems that have yet to be solved. The purification and recycling of the spent electrolyte as a regenerated medium by removing its fission products (FP) must be further investigated to reduce the volume of high-level radioactive waste (HLW). Some FP elements dissolved in the medium are apt to remain in the spent electrolyte after recovering actinoid elements. To remove such FP, the zeolite sorption is applied as it is considered the most suitable method, but its concept should be modified in order to reduce the generating waste volume. As one of the solutions, the electrolyte recycle process by phosphates is being developed. In this paper, the author has discussed the pyroprocess development, highlighting the spent electrolyte treatment from the viewpoint of economical and environmental load reduction.
Sanada, Hiroyuki; Sugita, Yutaka; Daimaru, Shuji; Matsui, Hiroya; Kashiwai, Yoshio*
Journal of MMIJ, 126(10,11), p.569 - 576, 2010/10
When the structures such as rock slopes, underground caverns for the geological disposal of high level radioactive waste and underground power plants are constructed, the potential for displacement and damage in the surrounding rock mass is increased due to stress concentration and creep phenomenon. Therefore, the long-term monitoring of rock stability for construction of rock cavern and slopes is important to maintain stability of rock structures. Recently, development of sensors that use optical fiber have expanded mainly in the field of civil engineering and, in rock and soil mechanics, since several parameters such as temperature, strain, pressure, pH etc. can be obtained by using backscattered light in optical fibers. Additionally, some important advantages using optical fiber are its high resistance to the electric insulation failure, long-term endurance and ability to transmit data over long distances. This paper describes development of a multiple-type displacement sensor using FBG, which has potential for the long-term durability and high accuracy. Laboratory tests were carried out to investigate the relational expression computed from the relationship of the variation in the Bragg wavelength, temperature and displacement. Accuracy of the prototype developed in this research is better than 0.5% or 1/100 mm. The in situ tests involving long-term monitoring using boreholes were conducted to confirm the workability and applicability of the prototype. From the results of the in situ tests, workability is equivalent to the extensometers usually used for long-term monitoring, and the displacement computed from the variation of Bragg wavelength is almost equal to the artificially induced deformation.
Saito, Hiroshi; Taki, Tomihiro
Journal of MMIJ, 126(6), p.239 - 242, 2010/05
Ningyo-toge Environmental Engineering Center, Japan Atomic Energy Agency (JAEA) has maintained and preserved the Ningyo-toge and Togo Mines under the related laws, including the Mine Safety Law. JAEA has been planning to close these Mines to prevent mine-pollution and reduce radiological impact to as low as achievably possible, for lasting protection of individuals and the environment. Among the mine-related facilities that are subject to environmental remediation, the Mill Tilings Pond is given the top priority. So far, basic concept has been discussed in parallel with data acquisition and designing for some of remediation activities.
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.
Sanada, Hiroyuki; Niunoya, Sumio*; Matsui, Hiroya; Fujii, Yoshiaki*
Journal of MMIJ, 125(10,11), p.530 - 539, 2009/10
Understanding initial stress in underground is important for construction of HLW repository. Evaluation of initial stress around Horonobe URL was carried out in order to understand initial stress condition and applicability of AE, DSCA and hydraulic fracturing (HF) methods to Neogene sedimentary rock. Initial stress values obtained from AE method is smaller than overburden pressure due to time dependency of Kaizer effect. Principal stress values by DSCA are similar to those by HF tests. Directions of maximum horizontal principal stresses are approximately in E-W and corresponded to HF results. Horizontal maximum and minimum principal stresses increase linearly in HF results. Deviatoric stress is acting at shallow depth. Initial stress condition approaches hydrostatic condition with depth. Direction of maximum horizontal principal stress was in E-W direction which was similar to tectonic movement around Horonobe URL by triangular surveying.
Sato, Akira*; Arimizu, Takuto*; Yonemura, Hirotaka*; Sawada, Atsushi
Journal of MMIJ, 125(4,5), p.146 - 155, 2009/04
The advection and dispersion of contaminated materials in a rock mass are one of the important factors to evaluate the characteristics of the rock mass as a natural barrier function for a radioactive waste disposal project. In this study, X-ray CT method was applied to evaluate the advection and dispersion of solute in the crack which exists in rock mass. In order to visualize advection and dispersion phenomena, the tracer migration test have been conducted and tracer migration process was visualized by X-ray CT scanner. Here, an indicator, coefficient of tracer density increment, was newly introduced to analyze tracer migration. This is the indicator that represents the density of the tracer in the crack, and the evaluation of the density distribution of the tracer becomes possible. In this study, the influences of the crack aperture to the tracer migration process are discussed.
Sato, Haruo
Journal of MMIJ, 125(1), p.1 - 12, 2009/01
Among the properties for controlling radionuclide migration of bentonite which is used as a buffer material composing engineered barriers for the geological disposal of high-level radioactive waste, studies on the water penetration, swelling, chemical buffering and nuclide migration retardation properties reported so far were reviewed. Additionally, what was clarified at the moment and future extension were summarized. After 2000, studies for saline groundwater conditions have been powerfully conducted, and it is understood that saline groundwater conditions affect all properties described above. Continuing these studies in the future, studies on the long-term behaviour considered the effect of alteration are necessary.
Kurihara, Arata; Amano, Kenji; Liu, C.*; Koike, Katsuaki*
Journal of MMIJ, 124(12), p.710 - 718, 2008/12
The spatial distribution of hydrogeologically-relevant geological structures such as fracture and fault is usually very heterogeneous, varying, in general, according to geological history, scale of observation and rock type. With the objective of improving analytical methods to better understand structural heterogeneities, this paper describes the results of investigations of the spatial relationship between regional geological structures (Tsukiyoshi fault and Tsukiyoshi paleo-channel) and fracture density with special emphasis on low-angle fractures in the Toki granite, central Japan. As a result of the analysis, positive correlations between average of fracture spacing data and the horizontal distances from two regional geological structures have been observed. Because the positive correlations can be approximated with a polynomial function of the response surface, we have obtained an improved understanding of the spatial distribution of low-angle fractures with respect to the location of regional geological structures. We have interpreted that the observed spatial distribution of low-angle fracture density conforms to the tectonic setting, on the assumption that the Tsukiyoshi fault and Tsukiyoshi paleo-channel are probably associated with the pull-apart basin by strike-slip faulting from the past investigations and geophysical surveys for this research area. In addition, the proposed spatial modeling techniques and geological interpretations are able to evaluate certainty of interpreted faults and fractures distributions, quantify general trend in structural heterogeneities and detect unknown faults.
Hashiba, Kimihiro; Sato, Toshinori
Journal of MMIJ, 124(3), p.205 - 212, 2008/03
Time-dependent behavior and failure process of deep vertical shaft was simulated with the aid of non-linear theological constitutive equation of rock. This simulation focused on the effect of gravity and the deformation behavior parallel to the direction of excavation, which has hardly been examined with horizontal roadway or tunnel. Simulation with the model of 1000 m deep vertical shaft was carried out, and the effect of rock properties and rock stress conditions was examined. It was found that time-dependency, ductility, Poisson's ratio of rock mass and the ratio between horizontal and vertical rock stresses had an effect on failure process around the bottom of vertical shaft.
