Sapporo, Japan
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Oikawa H.,Akita University | Ogino T.,Akita University | Tsushima M.,Akita National College of Technology | Komatsu J.,Okuyama Boring Co. | Igarashi M.,Dia consultants Co.
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2012

In this paper, vacuum consolidation accompanied by the substitution of pore water with air is called "the air inflow vacuum consolidation". In this vacuum consolidation, inflow of air into the soil mass is permitted during consolidation. Due to this inflow of air, pore water in the soil mass is replaced by the air and drying shrinkage of the soil mass occurs, resulting in the considerably large acceleration of settlement. This phenomenon was accidentally found in the laboratory vacuum consolidation tests which were conducted for examining the effects of vacuum consolidation on peats. In this paper, presented are the characteristics of the air inflow vacuum consolidation. Copyright © 2012 by the International Society of Offshore and Polar Engineers (ISOPE).


Aoyagi K.,Japan Atomic Energy Agency | Tsusaka K.,INPEX Corporation | Nohara S.,Japan Central Research Institute of Electric Power Industry | Kubota K.,Japan Central Research Institute of Electric Power Industry | And 3 more authors.
ISRM International Symposium - 8th Asian Rock Mechanics Symposium, ARMS 2014 | Year: 2014

In the construction of any deep underground facility such as repository for high-level radioactive waste (HLW) disposal, significant changes in hydrogeomechanical properties around excavated galleries can be expected. This zone is called an Excavation Damaged Zone (EDZ). For the safety of HLW disposal, it is necessary to investigate the extent and hydrogeomechanical characteristics of an EDZ. In this research, the authors conducted in situ surveys such as seismic refraction surveying, geological mapping of the galleries, borehole television surveying, and hydraulic testing in the Horonobe Underground Research Laboratory. From the results of these surveys, the authors concluded that the extent of an EDZ, the area with a high-density of fractures, resulting in high hydraulic conductivity, was estimated to be about 0.2 to 1.2 m into the rock wall of the gallery. The authors also compiled the information of the extent of an EDZ and the hydrogeomechanical properties inside and outside of an EDZ as a conceptual model. Since the conceptual models provide the basic idea for determining flow and solute transport in an EDZ, the result of this research provides a useful data for safety assessment of HLW disposal. © 2014 by Japanese Committee for Rock Mechanics.


Mitsuia Y.,Hokkaido University | Harab S.,Dia Consultants Co. | Akabanea K.,Hokkaido University | Kodamaa J.,Hokkaido University | And 3 more authors.
ISRM International Symposium - 8th Asian Rock Mechanics Symposium, ARMS 2014 | Year: 2014

Surfaces of rock slopes in a cold region often get frozen in winter. Therefore, understanding time-dependent behavior of frozen rock as well as that of unfrozen rock is significant for long-term stability assessment of the rock slopes. In this study, creep tests were carried out on Shikotsu welded tuff under dry and wet conditions at -20 °C (253 K) to clarify effect of water content on the time-dependent behavior of frozen rock. The results showed that deformation of frozen wet specimens was much more than that of frozen dry specimens. It was also found that axial strain rate-axial creep strain curves of the frozen wet specimens were different from those of the frozen dry specimens. Ratio of tertiary creep region of frozen wet specimens was relatively longer. These differences can be explained by existence of pore ice. Furthermore, creep life of un-failure specimens could be estimated with axial strain rate because creep life showed negative correlation with the axial strain rate in the early stage. Based on both observed creep life of rupture specimens and estimated creep life of un-failure specimens, the creep life of frozen wet specimens was expected to be shorter than that of frozen dry specimens at creep stress below about 50% of uniaxial compressive strength of frozen wet specimens. This result indicates that the effect of water content should be investigated for long-term stability assessment of rock slopes in a cold region. © 2014 by Japanese Committee for Rock Mechanics.


Kawaida M.,Central Nippon Expressway Co. | Kosaka T.,Dia Consultants Co. | Yamada K.,Central Nippon Expressway Co. | Nakakuma K.,Maruyama Industry Co.
Zairyo/Journal of the Society of Materials Science, Japan | Year: 2012

Maizuru-Wakasa expressway was constructed on the soft ground area consisting a thick layer of peat and soft clay. In trial embankment construction, a large lateral displacement and settlement due to embankment load were observed. Therefore, vacuum consolidation (air-water separation system type) was selected to apply to another trial area nearby the previous one to improve the ground for embankment construction. It was found that the vacuum pressure could maintain at high level even after a successive consolidation settlement up to about 10m, A significantly incremental soil strength after consolidation settlement were observed. The analysis of soil strength increment induced by vacuum consolidation compared to another case history was analyzed and described in this paper. © 2012 The Society of Materials Science, Japan.


Matsu'ura T.,Japan Nuclear Energy Safety Organization | Furusawa A.,Geological Survey of Japan | Shimogama K.,Dia Consultants Co. | Goto N.,Chiyoda Corporation | Komatsubara J.,Geological Survey of Japan
Quaternary Geochronology | Year: 2014

We investigated late Quaternary deep-sea sequences of the C9001C cores (D/V Chikyu shakedown cruise) to refine the tephrostratigraphy and reconsider the marine terrace chronology along the Pacific coast of northern Honshu, Japan. We identified 16 concentrations (spikes) of glass shards (numbered G1-G16 from top to bottom), which correspond to 12 visible tephras and 4 non-visible tephras (cryptotephras). We correlated several spikes with known dated tephras: G1 with Towada-Ofudo (To-Of: last MIS 3, ≥32ka), G2 with Shikotsu-1 (Spfa-1: mid MIS 3, ≥42-44ka), G3 with Aso-4 (MIS 5b, 87ka), G4 with Toya (MIS 5d, 106ka), G9 with White Pumice (WP: mid MIS 7, 220ka), G12 or G13 with ODP794 2H-2-120 (mid MIS 8, 274-283ka), and G14 with Shiobara-Otawara (So-OT: mid MIS 9, 320ka). We classified spike G6 as a turbidite. The two lowest of these tephras, ODP794 2H-2-120 and So-OT, were assigned to MIS 7 in a previous age model on the basis of the first occurrence of Emiliania huxleyi. However, our tephra-based age model is consistent with the last occurrence of Proboscia curvirostris, and we assigned the core sediment corresponding to MIS 7 from a previously reported segment 55m long to a younger segment 22m long, and then verified that the sedimentation rate was constant through the core. We used the newly obtained age for the WP tephra, along with outcrop and borehole core evidence, to reconsider the marine terrace chronology in the Kamikita Plain. A marine terrace that was previously assigned to MIS 7 with a possible vertical fault offset was reinterpreted as two separate terraces, one correlated with MIS 7e or 7c and the other with MIS 9. Regional uplift rates based on the revised terrace chronology and shoreline angle elevations appear to have been fairly steady at 0.18-0.36m/ky during the late Quaternary. © 2014 The Authors.


Watada S.,University of Tokyo | Kusumoto S.,University of Tokyo | Kusumoto S.,DIA Consultants Co. | Satake K.,University of Tokyo
Journal of Geophysical Research: Solid Earth | Year: 2014

Systematic tsunami traveltime delays of up to 15min relative to the numerically simulated long waves from the 2010 Chilean and 2011 Tohoku-Oki earthquakes were widely observed at deep ocean tsunamimeters. Enigmatic small negative phases appearing before the main peak were commonly found only at the trans-oceanic locations. The frequency dependence of the measured tsunami phase velocities shows reverse dispersions at long periods, i.e., the tsunami speed becomes slower at periods beyond 1000s. This is consistent with the phase velocities of a tsunami mode coupled with a self-gravitating elastic Earth, suggesting that the effects of compression and dilatation of seawater, elastic tsunami loadings on a solid Earth, and the geopotential variations associated with the motion of mass during tsunami propagation are responsible for the traveltime delays and the initial negative phases. Simple 1-D tsunami propagation tests confirm that the reverse dispersion creates a small negative phase that precedes the main peak at large distances. A new method to simulate tsunami waveforms on real ocean bathymetry that takes into account seawater compressibility, the elasticity of the Earth, and geopotential perturbations has been developed by applying a phase correction to the simulated long waves. The simulated waveforms, in which phase corrections are applied for the dispersion effects, accurately reproduce the observed waveforms, including a small initial negative phase that appears at distant locations. The traveltime difference between the observed and simulated waveforms has been decreased to less than 5min and the waveform difference between them remarkably diminishes. ©2014. American Geophysical Union. All Rights Reserved.


Tabelin C.B.,Hokkaido University | Hashimoto A.,DIA Consultants Co. | Igarashi T.,Hokkaido University | Yoneda T.,Hokkaido University
Science of the Total Environment | Year: 2014

Sedimentary rocks of marine origin excavated in tunnel projects were recently identified as potentially hazardous because they could release significant amounts of toxic trace elements when exposed to the environment. This study investigated the leaching characteristics of B, As, Se and the major coexisting ions under various conditions to identify the factors and processes controlling their evolution in the leachate. In addition, we evaluated whether the parameters of the currently used leachability test for excavated rocks were adequate. Although the leachabilities of B, As and Se similarly increased at longer contact times, only those of B and As were influenced by the mixing speed and/or liquid-to-solid ratio (L/S). The majority of trace elements dissolved in the leachate originated from the dissolution of soluble salts formed from seawater of the Cretaceous trapped during the formation of the sedimentary rocks. Moreover, the alkaline pH of the leachates could be attributed to the simultaneous dissolutions at varying degrees of the mineral components of the rocks as well as the precipitation of clay minerals. In the leaching test of excavated rocks for regulatory purposes, the best values of contact time and mixing speed should represent conditions of the highest trace element extractabilities, which in this study were found at longer contact times (>48 h) and the fastest mixing speed (200. rpm). The most appropriate L/S for the leaching test is 10 because it was around this L/S that the extractabilities and leaching concentrations of the trace elements were simultaneously observed at their highest values. © 2013 Elsevier B.V.


PubMed | DIA Consultants Co. and Hokkaido University
Type: | Journal: The Science of the total environment | Year: 2014

Sedimentary rocks of marine origin excavated in tunnel projects were recently identified as potentially hazardous because they could release significant amounts of toxic trace elements when exposed to the environment. This study investigated the leaching characteristics of B, As, Se and the major coexisting ions under various conditions to identify the factors and processes controlling their evolution in the leachate. In addition, we evaluated whether the parameters of the currently used leachability test for excavated rocks were adequate. Although the leachabilities of B, As and Se similarly increased at longer contact times, only those of B and As were influenced by the mixing speed and/or liquid-to-solid ratio (L/S). The majority of trace elements dissolved in the leachate originated from the dissolution of soluble salts formed from seawater of the Cretaceous trapped during the formation of the sedimentary rocks. Moreover, the alkaline pH of the leachates could be attributed to the simultaneous dissolutions at varying degrees of the mineral components of the rocks as well as the precipitation of clay minerals. In the leaching test of excavated rocks for regulatory purposes, the best values of contact time and mixing speed should represent conditions of the highest trace element extractabilities, which in this study were found at longer contact times (>48 h) and the fastest mixing speed (200 rpm). The most appropriate L/S for the leaching test is 10 because it was around this L/S that the extractabilities and leaching concentrations of the trace elements were simultaneously observed at their highest values.


Tabelin C.B.,Hokkaido University | Hashimoto A.,DIA Consultants Co. | Igarashi T.,Hokkaido University | Yoneda T.,Hokkaido University
Science of the Total Environment | Year: 2014

Sedimentary rocks excavated in Japan from road- and railway-tunnel projects contain relatively low concentrations of hazardous trace elements like boron (B), arsenic (As) and selenium (Se). However, these seemingly harmless waste rocks often produced leachates with concentrations of hazardous trace elements that exceeded the environmental standards. In this study, the leaching behaviors and release mechanisms of B, As and Se were evaluated using batch leaching experiments, sequential extraction and geochemical modeling calculations. The results showed that B was mostly partitioned with the residual/crystalline phase that is relatively stable under normal environmental conditions. In contrast, the majority of As and Se were associated with the exchangeable and organics/sulfides phases that are unstable under oxidizing conditions. Dissolution of water-soluble phases controlled the leaching of B, As and Se from these rocks in the short term, but pyrite oxidation, calcite dissolution and adsorption/desorption reactions became more important in the long term. The mobilities of these trace elements were also strongly influenced by the pH of the rock-water system. Although the leaching of Se only increased in the acidic region, those of B and As were enhanced under both acidic and alkaline conditions. Under strongly acidic conditions, the primarily release mechanism of B, As and Se was the dissolution of mineral phases that incorporated and/or adsorbed these elements. Lower concentrations of these trace elements in the circumneutral pH range could be attributed to their strong adsorption onto minerals like Al-/Fe-oxyhydroxides and clays, which are inherently present and/or precipitated in the rock-water system. The leaching of As and B increased under strongly alkaline conditions because of enhanced desorption and pyrite oxidation while that of Se remained minimal due to its adsorption onto Fe-oxyhydroxides and co-precipitation with calcite. © 2013 Elsevier B.V.


PubMed | DIA Consultants Co. and Hokkaido University
Type: | Journal: The Science of the total environment | Year: 2014

Sedimentary rocks excavated in Japan from road- and railway-tunnel projects contain relatively low concentrations of hazardous trace elements like boron (B), arsenic (As) and selenium (Se). However, these seemingly harmless waste rocks often produced leachates with concentrations of hazardous trace elements that exceeded the environmental standards. In this study, the leaching behaviors and release mechanisms of B, As and Se were evaluated using batch leaching experiments, sequential extraction and geochemical modeling calculations. The results showed that B was mostly partitioned with the residual/crystalline phase that is relatively stable under normal environmental conditions. In contrast, the majority of As and Se were associated with the exchangeable and organics/sulfides phases that are unstable under oxidizing conditions. Dissolution of water-soluble phases controlled the leaching of B, As and Se from these rocks in the short term, but pyrite oxidation, calcite dissolution and adsorption/desorption reactions became more important in the long term. The mobilities of these trace elements were also strongly influenced by the pH of the rock-water system. Although the leaching of Se only increased in the acidic region, those of B and As were enhanced under both acidic and alkaline conditions. Under strongly acidic conditions, the primarily release mechanism of B, As and Se was the dissolution of mineral phases that incorporated and/or adsorbed these elements. Lower concentrations of these trace elements in the circumneutral pH range could be attributed to their strong adsorption onto minerals like Al-/Fe-oxyhydroxides and clays, which are inherently present and/or precipitated in the rock-water system. The leaching of As and B increased under strongly alkaline conditions because of enhanced desorption and pyrite oxidation while that of Se remained minimal due to its adsorption onto Fe-oxyhydroxides and co-precipitation with calcite.

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