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Ioka S.,Horonobe Research Institute for the Subsurface Environment | Sakai T.,Horonobe Research Institute for the Subsurface Environment | Igarashi T.,Hokkaido University | Ishijima Y.,Horonobe Research Institute for the Subsurface Environment
Environmental Earth Sciences | Year: 2011

The in situ redox potential (Eh) in anoxic groundwater with high methane and iron contents (approximately 12.3 and 28.4 mg/L, respectively) was potentiometrically measured to identify the processes that control Eh. The measured Eh ranged from -213 to -187 mV; it had an inverse correlation with the concentration of methane and no correlation with that of iron. The saturation indices indicate that goethite and amorphous FeS were nearly at solubility equilibrium. A comparison of the measured Eh with those calculated for the particular redox pairs indicates that either Fe2+/FeOOH or CH4/CO2, but not sulfur redox pairs, controlled the measured Eh. The inverse relationship between measured Eh and methane concentration suggests possible control of the redox conditions by the CH4/CO2 redox pair. Furthermore, the equilibrium solubility state of goethite, which has higher crystallinity and lower solubility than Fe(OH)3 indicates that the iron reaction was electrochemically irreversible. This further supports the contribution of the CH4/CO2 pair to controlling the measured Eh of groundwater. © 2010 Springer-Verlag.

Nara Y.,Kyoto University | Oe Y.,Kyoto University | Murata S.,Kyoto University | Ishida T.,Kyoto University | And 2 more authors.
Zairyo/Journal of the Society of Materials Science, Japan | Year: 2014

It is important to evaluate the long-term stability of rock materials for the purpose of ensuring the long-term integrity of structures in a rock mass. In this study, we showed an evaluation method of the long-term strength of rock considering the change of the surrounding environmental conditions. It was shown that the long-term strength of rock decreased remarkably when the environmental condition changed from air to water condition and from low temperature to high temperature condition. This is due to the acceleration of subcritical crack growth in rock, because the relationship between the crack velocity and the stress intensity factor for subcritical crack growth is dependent on the temperature and existence of water. It is also recognized that the values of long-term strength of rock are affected significantly by the highest temperature and water if the rock can be surrounded by water. It is concluded that the long-term strength of rock under water environment with high temperature is important for ensuring the long-term integrity of structures in a rock mass. © 2014 The Society of Materials Science, Japan.

Tabelin C.B.,Hokkaido University | Igarashi T.,Hokkaido University | Yoneda T.,Hokkaido University | Tamamura S.,Horonobe Research Institute for the Subsurface Environment
Engineering Geology | Year: 2013

We have developed the adsorption-layer system for the simple and effective disposal of excavated rocks containing hazardous pollutants like arsenic (As). In this study, adsorption properties of natural and artificial materials including their performance in an actual altered rock-adsorption layer setup were evaluated. The adsorption of As[V] and As[III] onto all adsorbents fitted well with the Langmuir isotherm, indicating monolayer adsorption and progressive saturation of adsorption sites. All adsorbents were capable of As[V] and As[III] sequestration, but As[V] was more strongly adsorbed than As[III] based on the Langmuir isotherm. Also, artificial adsorbents were more efficient per unit weight than the natural adsorbent. Using the Langmuir isotherms and sequential extraction results, appropriate adsorbent dosages were estimated and then applied to an actual altered rock-adsorption layer column setup. The leaching concentration of As was lowered below 10 μg/L throughout the experiment regardless of the kind of adsorbent used. This suggests that the adsorption-layer system is a promising alternative to special landfills in the disposal of excavated rocks enriched with As. © 2013 Elsevier B.V.

Fukuda D.,Hokkaido University | Ikezawa J.,Hokkaido University | Kaneko K.,Horonobe Research Institute for the Subsurface Environment | Kodama J.,Hokkaido University | Fujii Y.,Hokkaido University
ISRM International Symposium - 8th Asian Rock Mechanics Symposium, ARMS 2014 | Year: 2014

In blasting, cylindrical charge is generally applied in terms of energy efficiency. The dynamic fracturing in rock due to detonation of high-explosive involves quite fast process and extremely complex fracturing pattern. In addition, detailed fracturing process is generally not observable. Thus, blasting design tends to be based on empirical knowledge or law. It is also well known that fracturing process envisioned here depends on the applied pressure wave forms characterized by such as detonation property and amount of applied explosive. These in turn make the design optimization of blasting quite difficult and, even for the simplest blasting problem with a single free face, the fracturing mechanism has not been clarified yet. Therefore, it is of paramount importance to investigate the fracturing process due to blasting in detail for various types of applied pressure wave forms. For this purpose, application of numerical simulation is one of the most promising approaches. This paper proposed a method for the simulation of dynamic fracturing process through axisymmetric finite element formulation in which the initiation, propagation, branching and coalescence of fractures in heterogeneous rock can be analyzed. In particular, blasting a cylindrical charge through bottom priming in a cylindrical rock specimen was analyzed considering the difference of load configuration characterized by length of applied explosive. It was clarified that the resultant fracturing patterns were strongly dependent on the length of applied explosive. In addition, cross-shaped fractures occurring on the free face were successfully simulated by the proposed method, which were observed in the field-scale blasting with a cylindrical charge. Therefore, the applicability of the proposed method was validated and it can give a deep insight for understanding the dynamic fracturing process in rock due to blasting with a cylindrical charge. © 2014 by Japanese Committee for Rock Mechanics.

Ioka S.,Horonobe Research Institute for the Subsurface Environment | Sakai T.,Horonobe Research Institute for the Subsurface Environment | Igarashi T.,Hokkaido University | Ishijima Y.,Horonobe Research Institute for the Subsurface Environment
Environmental Monitoring and Assessment | Year: 2011

This study was undertaken to investigate the redox potential (Eh) of sulfidic groundwater in unconsolidated sediments. The Eh was determined by long-term (several days to several weeks) continuous in situ potentiometric measurements using a platinum (Pt) electrode. The Eh values measured in two monitoring campaigns were -259 and -202 mV, respectively. Chemical analysis of groundwater showed that the redox species in the groundwater were sulfide (S2-) and iron, respectively. The saturation indices calculated from the chemical analysis results indicated that FeS(am) and mainly mackinawite were close to equilibrium in the analyzed waters. Comparison of the measured Eh values with those calculated using different redox couples revealed that the Eh values measured in the first monitoring campaign were nearly equal to those calculated using HS-/SO4 2-, S 2-/SO4 2-, FeS am/SO 4 2-, and mackinawite/SO 4 2- redox couples; on the other hand, the Eh values measured in the second monitoring campaign were almost consistent with those measured using the FeS2/SO 4 2- redox couple. The good fit between the measured Eh values and the theoretical calculated Eh values suggests that the sulfur system is related to the Eh value of sulfidic groundwater in unconsolidated sediments. © 2010 Springer Science+Business Media B.V.

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