基本情報

所属

• 工学研究院　環境循環システム部門　地圏循環工学分野

職名

• 准教授

学位

• 博士（工学）（北海道大学）

ホームページURL

http://rock.eng.hokudai.ac.jp/japanese.html

J-Global ID

• 200901029265880777

研究キーワード

• 岩盤力学   Rock Mechanics   

研究分野

• エネルギー / 地球資源工学、エネルギー学

担当教育組織

•  学士課程　工学部
•  修士課程　工学院
•  博士課程　工学院

学歴

•         - 1992年   北海道大学   工学研究科   資源開発工学専攻
•         - 1992年   北海道大学
•         - 1989年   北海道大学   工学研究科   資源開発工学専攻
•         - 1989年   北海道大学
•         - 1987年   北海道大学   工学部   資源開発工学科
•         - 1987年   北海道大学

所属学協会

• 日本材料学会   土木学会   資源・素材学会   国際岩の力学連合会(ISRM)   International Society of Rock Mechanics   

研究活動情報

論文

• Time-dependence of mechanical behavior of Shikotsu welded tuff at sub-zero temperature

  児玉 淳一

  Cold Regions Science and Technology in press 2019年 [査読有り][通常論文]
  
• Variation in the Permeability of Intact and Fractured Rocks due to Transient Disturbances in Axial Stress or Pore Pressure

  児玉 淳一

  Advances in Civil Engineering 2019 Article ID 1312746, doi:/10.11 2019年 [査読有り][通常論文]
  
• Development of a GPGPU-Parallelized Hybrid Finite-Discrete Element Method for Modeling Rock Fracture

  児玉 淳一

  International Journal for Numerical and Analytical Methods in Geomechanics 10 1797 - 1824 2019年 [査読有り][通常論文]
  
• Influences of water vapor on roof fall accidents in selected underground coal mines in Malawi

  児玉 淳一

  Advances in Civil Engineering 2019 Article ID 5350686 doi:/10.115 2019年 [査読有り][通常論文]
  
• Tangent modulus method – An original method to measure in-situ rock stress

  Y. Fujii, M. Makasi, J. Kodama, D. Fukuda, K. Goto, S. Kumakura, M. Kanaoka, A. B.N. Dassanayake

  Tunnelling and Underground Space Technology 82 148 - 155 2018年12月 [査読有り][通常論文]
   

  © 2018 Elsevier Ltd This paper proposed Tangent Modulus Method (TMM) which is an improved oriented core method to determine in-situ rock stresses. In this approach, the cylindrical specimens prepared along different directions from thick core samples were uniaxially compressed twice to a given stress level. The stress value of the bending point in the first loading cycle of the stress-tangent modulus curve is considered as the normal component of the in-situ rock stress along the drilled direction of the specimen. Four types of rocks from soft porous tuff and sandstone to hard crystalline granite was investigated to evaluate the potential of this method. The effects of changes in strain rate, temperature, water content, confining and pore pressure, and stresses larger than the preload on the stress value of the bending point were experimentally investigated on preload specimens to investigate their influence on TMM. Comparison of the stress measurement results by TMM and an overcoring method at AK tunnel in Hokkaido, Japan was also performed to validate the TMM.
• Monitoring and evaluation of simulated underground coal gasification in an ex-situ experimental artificial coal seam system

  Fa-qiang Su, Akihiro Hamanaka, Ken-ichi Itakura, Wenyan Zhang, Gota Deguchi, Kohki Sato, Kazuhiro Takahashi, Jun-ichi Kodama

  Applied Energy 223 82 - 92 2018年08月01日 [査読有り][通常論文]
   

  In this study, to better simulate underground coal gasification (UCG), an artificial coal seam was constructed to use as a simulated underground gasifier, which comprised coal blocks excavated from the coal seam. This study reports the process and results of three independently designed experiments using coaxial-hole and linking-hole UCG models: (a) a coaxial model using a coaxial pipeline as a gasification channel, (b) a coaxial model using the coaxial pipeline combined with a bottom cross-hole, and (c) a linking-hole model using a horizontal V-shaped cross-hole. In the present work, the fracturing activities and cavity growth inside the reactor were monitored with acoustic emission (AE) technologies. During the process, the temperature profiles, gas production rate, and gas content were measured successively. The results show that AE activities monitored during UCG process are significantly affected by operational variables such as feed gas rate, feed gas content, and linking-hole types. Moreover, the amount of coal consumed during UCG process were estimated using both of the stoichiometric approach and balance computation of carbon (C) based on the product gas contents. A maximum error of less than 10% was observed in these methods, in which the gas leakage was also considered. This demonstrates that the estimated results using the proposed stoichiometric approach could be useful for evaluating energy recovery during UCG.
• Geological and Geotechnical Evaluation of Gully Erosion at Nguzu Edda, Afikpo Sub-Basin, Southeastern Nigeria

  児玉 淳一

  Journal of Environment and Earth Science 8 12 148 - 158 2018年 [査読有り][通常論文]
  
• Prevention of Catastrophic Volcanic Eruptions, Large Earthquakes underneath Big Cities and Giant Earthquakes at Subduction Zones

  Yoshiaki Fujii, Morteza Sheshpari, Jun-ichi Kodama, Daisuke Fukuda, Anjula BN Dassanayake

  Sustainability 10 1908 2018年 [査読有り][通常論文]
  
• Upper Bounds of Seismic Events in Induced Seismicity by Shale Gas Extraction, Carbon Capture and Storage, and Natural Magma Injection

  児玉 淳一

  Journal of Volcanology and Seismology in press 2018年 [査読有り][通常論文]
  
• Water drainage from Kushiro Coal Mine decreased on the day of all M ≥ 7.5 earthquakes and increased thereafter

  児玉 淳一

  Scientific Reports 8 16472 2018年 [査読有り][通常論文]
   

  The amount of water drainage from Kushiro Coal Mine in Hokkaido, Japan decreased on the day of all M >= 7.5 earthquakes with epicenters within 300 km of the mine during the monitoring period and increased after these earthquakes. This is a valuable finding which would give us a clue to understand pre- and post-seismic rockmass behaviors and contribute for progress in earthquake prediction in future.
• UCG模型試験における破砕炭と塊炭の燃焼・ガス化特性の比較

  児玉淳一, 立川多久登, 中良介, 濱中晃弘, 板倉賢一, 出口剛太, 福田大祐, 藤井義明

  Journal of MMIJ (Web) 134 7 2018年 [査読有り][通常論文]
  
  ダウンロード
• コンパクト同軸型石炭地下ガス化システムにおける燃焼・ガス化の制御に関する研究

  濱中晃弘, 蘇発強, 板倉賢一, 高橋一弘, 佐藤孝紀, 児玉淳一, 出口剛太

  Journal of the Mining and Materials Processing Institute of Japan 134 7 2018年 [査読有り][通常論文]
  
• Time-dependent tunnel deformations in homogeneous and heterogeneous weak rock formations

  Atsushi Sainoki, Shingo Tabata, Hani S. Mitri, Daisuke Fukuda, Jun-ichi Kodama

  COMPUTERS AND GEOTECHNICS 92 186 - 200 2017年12月 [査読有り][通常論文]
   

  To investigate long-term, time-dependent tunnel deformations, this study employs a non-linear theological model capable of considering the tertiary creep behaviour of the rock mass (Okubo and Fukui, 2006). A model parametric study is undertaken with a 30 numerical model encompassing a tunnel. The results show that the tunnel walls start to deform at an accelerating rate after a lapse of ten years. The results offer an explanation to previously reported tunnel instability cases. A 3D numerical model encompassing weak rock formation obliquely intersecting with the tunnel is then constructed. The analysis yields asymmetric wall deformation pattern, suggesting the need for optimizing rock supports. (C) 2017 Elsevier Ltd. All rights reserved.
• Evaluation of Coal Combustion Zone and Gas Energy Recovery for Underground Coal Gasification (UCG) Process

  Fa-qiang Su, Akihiro Hamanaka, Ken-ichi Itakura, Gota Deguchi, Kohki Sato, Jun-ichi Kodama

  ENERGY & FUELS 31 1 154 - 169 2017年01月 [査読有り][通常論文]
   

  During underground coal gasification (UCG) operations, evaluation of coal gasification cavity evolution and precise control of the underground reactor are important for efficient gasification. It is also essential to estimate the energy recovery of a UCG system and the whole gasification process to ensure an effective combustion and gasification rate. An experimental simulation of UCG using an artificial coal seam comprising a compacted broken coal block was conducted using ex situ UCG models. The main goal of the experiments was the establishment of evaluation methods for the gasification zone and energy recovery during UCG. To investigate the distribution and extent of fracture activity, and to evaluate the propagation of the combustion area in the UCG reactor, we used acoustic emissions (AE) monitoring. This was combined with traditional measurements of temperature variation and product gas content. This paper presents the results of AE analysis of the fracturing activities and damage mechanisms of the coal seam with respect to the UCG operations. From the results of AE source location, we found that the position and area of the crack concentration area, i.e., the gasification zone, can be inferred with comparative accuracy. This is important for in situ practical application of underground coal gasification. In addition, use of the distribution characteristics of AE information over time can also provide advanced warning, and help in timely adjustment of the operational parameters. The results of gas energy recovery were estimated with a proposed stoichiometric method based on measured product gas composition. Quantitative evaluation results include the gas quantities, coal consumption, and heating value yield of the produced synthesis gas. The coal consumption of the obtained energy recovery results also meets the estimated results when calculating the gasification volume with AE source locations (in an error range of about 10%). Therefore, the applied AE monitoring and gas energy recovery approaches may be considered attractive options for evaluating the coal gasification process and developing a safe and efficient UCG system.
• Effect of Injection Flow Rate on Product Gas Quality in Underground Coal Gasification (UCG) based on Laboratory Scale Experiment: Development of Co-axial UCG System

  Akihiro Hamanaka, Faqiang Su, Ken-ichi Itakura, Kazuhiro Takahashi, Jun-ichi Kodama, Gota Deguchi

  Energies 10 2017年 [査読有り][通常論文]
  
• Ex-situ Model Experiment for Development of Compact Underground Coal Gasification (UCG) System

  Akihiro Hamanaka, Faqiang Su, Ken-ichi Itakura, Kohki Satoh, Kazuhiro Takahashi, Gota Deguchi, Jun-ichi Kodama, Koutarou Ohga

  Modern Environmental Science and Engineering 2 599 - 605 2016年 [査読有り][通常論文]
  
• Fractured Rock Permeability as a Function of Temperature and Confining Pressure

  A. K. M. Badrul Alam, Yoshiaki Fujii, Daisuke Fukuda, Jun-ichi Kodama, Katsuhiko Kaneko

  PURE AND APPLIED GEOPHYSICS 172 10 2871 - 2889 2015年10月 [査読有り][通常論文]
   

  Triaxial compression tests were carried out on Shikotsu welded tuff, Kimachi sandstone, and Inada granite under confining pressures of 1-15 MPa at 295 and 353 K. The permeability of the tuff declined monotonically with axial compression. The post-compression permeability became smaller than that before axial compression. The permeability of Kimachi sandstone and Inada granite declined at first, then began to increase before the peak load, and showed values that were almost constant in the residual strength state. The post-compression permeability of Kimachi sandstone was higher than that before axial compression under low confining pressures, but lower under higher confining pressures. On the other hand, the permeability of Inada granite was higher than that before axial compression regardless of the confining pressure values. For the all rock types, the post-compression permeability at 353 K was lower than at 295 K and the influence of the confining pressure was less at 353 K than at 295 K. The above temperature effects were observed apparently for Inada granite, only the latter effect was apparent for Shikotsu welded tuff, and they were not so obvious for Kimachi sandstone. The mechanisms causing the variation in rock permeability and sealability of underground openings were discussed.
• A new approach to evaluate effective stress coefficient for strength in Kimachi sandstone

  A. B. N. Dassanayake, Yoshiaki Fujii, Daisuke Fukuda, Jun-ichi Kodama

  JOURNAL OF PETROLEUM SCIENCE AND ENGINEERING 131 70 - 79 2015年07月 [査読有り][通常論文]
   

  This paper is devoted to the experimental investigation of effective stress coefficient for peak and residual strengths of saturated Kimachi sandstone. Authors have described the Modified Failure Envelope Method (MFEM), which can be used to obtain the effective stress coefficients for peak and residual strengths (alpha(-Peak) and alpha(-Residual)). The effective stress coefficients for intact and fractured Kimachi sandstone (alpha(-Biot's) and alpha(-Fractured)) were also evaluated using conventional methods, and the data were compared with the coefficient values obtained by MFEM for the peak and residual strengths. The effective stress coefficient for intact rock, alpha(-Biot's) decreased with increasing confining pressure, and was in the range 1 > alpha(-Biot's) > 0.8. The effective stress coefficient for fractured rock, alpha(-Fractured), was larger than that for intact rock and was close to unity. The effective stress coefficient calculated for peak strengths, alpha(-Peak), using both the single and multistage MFEMs, decreased with increasing effective confining pressure and was in the range 0.8 > alpha(-Peak) > 0.4. For residual strength states, effective stress coefficient, alpha(-Residual), was between the peak strength value and that for intact rock. Based on the results, multistage MFEM is suitable for obtaining an effective stress coefficient for the peak strength, alpha(-Peak). An equation to obtain the effective stress coefficient from total confining pressure and pore pressure, and a method to choose the coefficients for elastic stress analyses and failure evaluations for intact rock structures or structures in rock mass were proposed. (C) 2015 Elsevier B.V. All rights reserved.
• The Deformation Modes of Rock Slopes due to Excavation in Mountain-Type Mines

  Najib, Daisuke Fukuda, Jun-Ichi Kodama, Yoshiaki Fujii

  MATERIALS TRANSACTIONS 56 8 1159 - 1168 2015年 [査読有り][通常論文]
   

  This paper discusses an investigation of mining-induced elastic deformation of a cut rock slope formed in a mountain-type mine using a two-dimensional finite element method. The horizontal elastic deformation mechanism is discussed, including the effects of the Poisson's ratio, slope angle and progression of the excavation. The results show a clear dependence of the deformation modes characterized by extension, contraction or shear distortion of rock mass, on these three effects, in which the direction of rock movement at the surface due to excavation was opposite. Four effects contribute to the deformation mechanism in mountain-type mines: the Poisson effect (PE), the distributed load effect (DLE), bending effects and shear distortion. Forward surface displacement of the cut rock slope was found to occur during the early stages of excavation due to the release of horizontal compressive stresses due to bending effects around the middle of the mountaintop. As the excavation progresses, forward or backward horizontal surface displacement was found to occur due to PE or DLE, respectively, which depends on the Poisson's ratio in the subsequent stages of excavation. Asymmetric stress release due to excavation affects the horizontal deformation of the mountain, and induces a moment enhancing the backward displacement due to shear distortion. It should be noted that the direction of the surface displacement of the rock slope could change from forward to backward as the excavation progresses, even though the rock slope may be stable. This is very important in the interpretation of surface displacement monitoring using the Automated Polar System and/or Global Positioning System. In the interpretation of the internal displacement measured using extensometers, we should consider extension during the early stages of excavation, followed by slight contraction during the latter stages, as a sign of a stable cut rock slope in a mountain type mine.
• 凍結融解履歴を受ける泥質片岩と花崗岩の変形挙動と破壊プロセス

  児玉淳一, 畔原孝典, 福田大祐, 藤井義明

  Journal of the Society of Material Science, Japan 63 3 219 - 226 2014年 [査読有り][通常論文]
   

  Fracture processes of argillaceous schist and granite subjected to freeze-thaw cycles were investigated based on their deformation behaviors. It was found that argillaceous schist showed apparent anisotropy in deformation. Significant extensile strain was observed in the direction perpendicular to the cleavage plane around -3°C in freezing process on the water-saturated specimen, followed by extensile plastic strain at the end of the cycle. No apparent extension and anisotropy were found on the water-saturated specimen of granite, but decrease in contraction rate was seen at -3°C in freezing process with AE activity. The extensile plastic strain of both rocks gradually increased with the number of freeze-thaw cycles, but magnitude of the plastic strain on argillaceous schist was much greater than that of granite. These results indicate that there might be common mechanism in fracture process between both rocks, but significant differences in deterioration rate. Deterioration of argillaceous schist is much faster because fracture mainly develops by extension of well-developed cleavage in the rock. It was concluded that weak plane such as cleavage strongly affected deterioration of rocks by freeze-thaw cycle. © 2014 The Society of Materials Science, Japan.
• Effects of confining pressure on the permeability of three rock types under compression

  A. K. M. Badrul Alam, Masaki Niioka, Yoshiaki Fujii, Daisuke Fukuda, Jun-ichi Kodama

  INTERNATIONAL JOURNAL OF ROCK MECHANICS AND MINING SCIENCES 65 49 - 61 2014年01月 [査読有り][通常論文]
   

  Triaxial tests were conducted on three different rocks, under confining pressures of 1-15 MPa at 295 K using an ultra-compact triaxial cell. The samples were held for 24 h under the target consolidation pressure, and then constant strain-rate compression was applied measuring permeability. The structural changes were measured by thin section image analysis and micro-focus X-ray computed tomography. For the Shikotsu welded tuff, the permeability decreased monotonously with axial compression, mainly due to pore collapse. For the Kimachi sandstone, the permeability first decreased with increasing axial stress, then began to increase when the total lateral strain recovered its value before the application of confining pressure, and then maintained an almost constant value in the post-peak region. The minimum and final permeability decreased with increasing confining pressure mainly due to compaction and large plastic deformation of clay cementing materials. For the lnada granite, the tendency of permeability change during axial compression was almost the same as for the Kimachi sandstone. The final permeability was larger than that before compression, and the permeability decreased with smaller confining pressure mainly due to a decrease in the number and width of rupture planes and the absence of axial cracks from biotite. The permeability, however, increased under larger confining pressures mainly due to the formation of subrupture planes caused by the high stress concentration at the rough and stiff rupture plane under large confining pressure. (C) 2013 Elsevier Ltd. All rights reserved.
• Estimation of Regional Stress State and Young’s Modulus by Back Analysis of Mining-Induced Deformation

  児玉 淳一

  International Journal of Rock Mechanics and Mining Sciences 63 1 - 11 2013年10月 [査読有り][通常論文]
   

  A method to evaluate regional stress state and Young's modulus by analyzing the mining-induced deformation of ground is proposed. The effect of changes in regional strain state due to tectonic plate motion can be accounted for using the proposed method. Mining-induced deformation can manifest itself as changes in ground surface geometry resulting from mining activity. There are three underlying factors that can contribute to the deformation, these being: displacement induced by the effect of gravity; displacement induced by the effect of horizontal regional strain; and, incremental change in the horizontal regional strain. Both regional strain and Young's modulus can be simultaneously estimated, because the displacement induced by the regional strain is independent of the Young's modulus and the displacement induced by the gravity is inversely proportional to the Young's modulus. The relative displacement arising from the mining excavation at the Torigatayama limestone mine in Japan has been measured by GPS. Both the regional stress state and Young's modulus were estimated by back analysis of the relative displacement using a 3-D finite element method. It was shown that back analysis based on changes in distance between the measurement points provides a more reliable estimation than that could be achieved based on the direct relative displacement. (C) 2013 Elsevier Ltd. All rights reserved.
• The effects of water content, temperature and loading rate on strength and failure process of frozen rocks

  J. Kodama, T. Goto, Y. Fujii, P. Hagan

  INTERNATIONAL JOURNAL OF ROCK MECHANICS AND MINING SCIENCES 62 1 - 13 2013年09月 [査読有り][通常論文]
   

  The effects of water content, temperature and loading rate on the strength and failure process of rock at sub-zero temperatures were investigated and are presented in this paper. Over the range of temperatures studied there was little change observed in the properties of dry rock. The presence of water in the rock, however, resulted in a marked increase in rock strength and the fracture initiation stress. Rock strength increased with amount of water present and the rate of load application, with the effect being exacerbated at the colder temperatures. Interestingly, the changes in strength were not uniform as there was a greater rate of increase in the tensile strength of rock with temperature than compressive strength. It is postulated that these changes in mechanical properties may be explained in part by a reduction in the stress concentration within the interstitial spaces and cracks of the rock samples tested. (C) 2013 Elsevier Ltd. All rights reserved.
• 岩石の強度に対して応力状態が影響するメカニズムを明らかにするための三次元弱面モデル

  藤井義明, 児玉淳一, 福田大祐

  ournal of the Mining and Materials Processing Institute of Japan 129 7 467 - 471 The Mining and Materials Processing Institute of Japan 2013年 [査読有り][通常論文]
   

  The 3-D weakness plane model was developed to clarify the mechanisms of influences of various stress states on the strength of rocks. The model assumes numerous planes of weakness whose directions are uniformly distributed in a rock; each plane slips or opens based on the Coulomb criterion with a tension cut-off; and the rock is regarded as failed when the ratio of the failed plane number to that of all planes reaches a certain value. The equal strength parameters were assigned to all planes and no complicated statistical functions are used. The model was applied to true triaxial compression, uniaxial tension, Brazilian and extension tests. The model was very simple but the effects of a stress state, namely, nonlinear increase of peak stress with small intermediate principal stress and nonlinear decrease with large intermediate principal stress in true triaxial tests, larger tensile strength by Brazilian tests than uniaxial tensile tests and the bilinear nature of peak stress in extension tests, were simulated very well. Distributions of stress and failed planes on the Schmidt net increased the understanding of the mechanism of the stress state effects on rock strength.
• 凍結した支笏溶結凝灰岩の力学的挙動の時間依存性

  三井善孝, 児玉淳一, 原翔平, 菅原隆之, 福田大祐, 藤井義明

  Journal of the Mining and Materials Processing Institute of Japan 129 7 433 - 439 The Mining and Materials Processing Institute of Japan 2013年 [査読有り][通常論文]
   

  Understanding time-dependent deformation of frozen rock is significant for the assessment of long-term stability of rock slopes in cold region. In this study, to clarify the time-dependent deformation of frozen rock and influence of water content on the deformation, a series of uniaxial compression tests and creep tests were carried out on Shikotsu welded tuff under the dry and wet conditions at -20℃ (-4°F). The uniaxial compressive strength (UCS) of frozen wet specimens was approximately equal to that of frozen dry specimens at the strain rate below 4.2×10^-6/s. However, the former was greater than the latter at higher strain rates. The creep life of frozen wet specimens was longer than that of frozen dry specimens at the stress level above 13.4 MPa. On the other hand, the former was shorter than the latter at lower stress levels. Deformation of frozen wet specimens was larger than that of frozen dry specimens. The frozen dry and wet specimens showed different axial strain rate-axial creep strain curves. These differences could be explained by the presence of pore ice. Therefore, water content of rock should be considered for the assessment of long-term stability of rock slopes in cold region.
• 一軸引張応力下における稲田花崗岩の疲労特性と寿命予測

  児玉淳一, 高坂恒輔, 福田大祐, 藤井義明

  Journal of the Mining and Materials Processing Institute of Japan 129 7 418 - 424 The Mining and Materials Processing Institute of Japan 2013年 [査読有り][通常論文]
   

  Uniaxial tension cyclic loading and creep tests were carried out on Inada granite aiming to clarify effects of stress amplitude and loading rate on fatigue behavior. Relationship between fatigue life, deformation behavior and AE activity were also examined. It was found that time to failure in cyclic loading test became shorter than that in creep test for low applied stress. This indicates stress amplitude has a significant effect on fatigue failure. The amount of fatigue damage per cycle increased with decrease in loading rate when the same maximum stress was applied. This is thought to be cause of decrease in fatigue life with decrease in loading rate. On the other hand, the amount of fatigue damage per cycle and fatigue life did not depend on loading rate when the same maximum stress ratio, which was normalized by the uniaxial tensile strength at each loading rate, was applied. Fatigue life of a specimen showing less strain increment tended to be longer and the relationship between the minimum value in the strain increment and fatigue life was represented by a line regardless of loading rate and maximum stress. AE event rate as well as strain increment was inversely proportion to life expectancy before failure. Ratio of AE event rate in unloading to loading began to increase just before failure. These results show that strain increment and AE event are useful parameter to predict fatigue failure.
• Sub-zero温度領域における支笏溶結凝灰岩と美唄砂岩の一軸圧縮強度と破壊プロセス

  児玉淳一, 原翔平, 三井善孝, 藤井義明

  Journal of the Mining and Materials Processing Institute of Japan 129 1 21 - 28 The Mining and Materials Processing Institute of Japan 2013年 [査読有り][通常論文]
   

  Strength and deformation of frozen rocks were investigated by uniaxial compression test and cyclic loading test at -20°C. Failure processes of Shikotsu welded tuff and Bibai sandstone were considered based on their deformation behaviors. Larger deformation of wet specimen was found than that of dry specimen in both rocks due to pore ices plastic deformation. However, effect of water content on strength depends on type of rocks. UCS of wet specimens of Shikotsu welded tuff was greater than that of dry specimens. In contrast, UCS of wet specimens was smaller on Bibai sandstone. The former phenomenon can be interpreted by inclusion effect of pore ice. The latter phenomenon can be explained due to stress corrosion by unfrozen water or reduction in friction coefficient of crack planes by pore ice.
• 新第三紀堆積軟岩における既設トンネルの拡幅事例にみる岩盤挙動について

  田村智樹, 太田光浩, 児玉淳一, 吉田豊

  Journal of MMIJ 128 2 65 - 71 The Mining and Materials Processing Institute of Japan 2012年 [査読無し][通常論文]
   

  Recently, old narrow tunnels are reused by widening their sections for economic efficiency. New design concept will be required in their construction because excavation damaged zone (EDZ) might be already formed around old tunnels. Especially, estimation of EDZ extent is necessary for safe construction and stability assessment of a widening tunnel. In this study, EDZ around an old tunnel constructed in the Neogene soft rock seventy years ago was estimated based on P-wave velocity and observation of the face during widening. Deformation caused by widening the old tunnel was also measured. It was found that EDZ estimated by reduction in P-wave velocity was in good agreement with that estimated by observation of the face. It was also found that deformation of the widening tunnel was much less than that of either the old tunnel or a new tunnel constructed near the widening tunnel. In the widening tunnel, most of EDZ had been excavated and non-damaged zone outer side of the EDZ had been little excavated. It can be expected that deformation of a widening tunnel is little when the section size of that is almost equal to extent of EDZ.
• Mechanical properties of abandoned and closed roadways in the Kushiro Coal Mine, Japan

  Yoshiaki Fujii, Yoji Ishijima, Yoshihisa Ichihara, Tamotsu Kiyama, Satoshi Kumakura, Michihiko Takada, Takayuki Sugawara, Takashi Narita, Jun-ichi Kodama, Masataka Sawada, Eiji Nakata

  INTERNATIONAL JOURNAL OF ROCK MECHANICS AND MINING SCIENCES 48 4 585 - 596 2011年06月 [査読無し][通常論文]
   

  The objective of this research is to clarify the mechanical properties and self-healing ability of the Excavation Damaged Zone (EDZ) around rock caverns in clastic-rock. Observations of nearly one hundred closed roadways up to fifty years old, which can be regarded as very severe EDZs with no initial sealability and are up to 300 m deep in clastic-rock, were made at the Kushiro Coal Mine, Japan, to accomplish the objective. Most old roadways were closed, though a few remain open. Closure of old roadways was mainly due to roof deflection and/or floor heave. Large plastic deformations dominated; however, severe fractures were seldom observed in closed old roadways. Rayleigh wave velocity and hydraulic conductivity in the closed old roadways were in the range of 0.3-1.2 km/s and 5 x 10(-7)-1 x 10(-7) m/s, respectively, and those in EDZ and EdZ (Excavation disturbed Zone) around recently excavated roadways were 1.1-1.8 km/s and 1 x 10(-8)-5 x 10(-8) m/s, respectively. The extent of EDZ around the present tailgate was in the range of 1-5 m. Mechanical excavation and prevention from water are suggested as the key points for long-term maintenance of rock repositories. Pressurization from inside the cavern to decrease the permeability of EDZ is proposed for maintenance of rock repositories in medium-hard clastic-rock masses at similar depths for long periods. (C) 2011 Elsevier Ltd. All rights reserved.
• Analysis of natural rock slope deformations under temperature variation: A case from a cool temperate region in Japan

  Azania Mufundirwa, Yoshiaki Fujii, Nariaki Kodama, Jun-ichi Kodama

  COLD REGIONS SCIENCE AND TECHNOLOGY 65 3 488 - 500 2011年03月 [査読無し][通常論文]
   

  In this paper, natural rock slope deformation across fractures predominantly in a chert rock mass was monitored using six surface fracture displacement sensors, and the deformations arising from thermal stresses were predicted using (5 m x 5 m) two-dimensional (2D) finite element (FE) plane strain analysis coupled with a model for rock mass expansion due to freezing of pore water. A new and simple method to minimize displacement proportional to temperature (due to thermal response of chert rock mass and sensor) was proposed. By applying the method, the corrected displacement, u', can be well recognized. Under u', clear rock mass movement, which could be related to fracture growth, was observed. In addition, progressive fracture opening and closure were noted. Results from this study indicate insignificant influences of weather conditions on fracture/rock mass movement. Furthermore, under numerical analysis (FE), in the rock mass model (with 1-m deep fracture), tensile stresses that were large enough to induce fracture growth appeared at the fracture tip when temperature lowered. And in the rock slope model (with 1-m deep fracture), small tensile stresses, which were sufficient to cause fracture growth along the planes of weakness, were observed. This research suggests that freezing effects on deformation of chert rock mass are insignificant, and we tentatively suggest that thermal fatigue predominantly caused the permanent fracture deformations. (C) 2010 Elsevier B.V. All rights reserved.
• 三軸圧縮破壊過程における岩石の透水性に封圧が及ぼす影響に関する研究

  高田 迪彦, 藤井 義明, 児玉 淳一

  Journal of MMIJ 127 3 151 - 157 資源・素材学会 2011年 [査読無し][通常論文]
   

  The permeability of Kimachi sandstone in triaxial compression failure process was investigated by laboratory experiments. Tests were carried out under a constant confining pressure of between 5.0 and 15.0 MPa with a constant pore pressure of 2.0 MPa until axial strain reached approximately 5.0%. The stress-strain relation was linear under low differential stress and gradually became nonlinear as peak differential stress approached. In the tests under confining pressure of 5.0 and 7.5 MPa, the permeability decreased in the elastic region and then increased as the peak strength approached. The permeability continued to increase at first in residual strength region, and then it decreased at axial strain of approximately 4.0%. In the tests conducted under higher confining pressure, the variation in the permeability was small until axial strain of 5.0%. It appeared that failure types were different depending on confining pressure from the observation of the thin sections made from the specimens after tests. In the tests under 5.0 MPa confining pressure, a macroscopic fault occurred in the test pieces. On the other hands it did not occur in the tests under higher confining pressures. It was suggested in the elastic FEM analyses that the failure types were influenced by the end constraint.
• 凍結融解作用を受ける岩石の破壊プロセスと耐久性の評価

  児玉 淳一, 中谷 匡志, 奈良 禎太, 後藤 龍彦, 藤井 義明, 金子 勝比古

  Journal of MMIJ 127 3 117 - 126 The Mining and Materials Processing Institute of Japan 2011年 [査読無し][通常論文]
   

  Durability evaluation of rocks subjected to freezing-and-thawing is important for stability assessment of a rock fill dam as well as rock slopes, especially in cold weather regions. In this study, freezing-and-thawing tests up to 300 cycles were carried out on twelve kinds of rock samples in order to characterize fracture propagation by freezing-and-thawing and evaluate the durability, and fracture propagation was observed. The fracturing process was characterized by macroscopic observation by digital camera and changes in physical properties. Fracture initiation and propagation in the specimen were also observed by using X-ray CT. It was found that the fracturing process depends on the rock type. For rocks which possess preferred orientation of pre-existing fractures and anisotropy of tensile strength, only one fracture propagated dominantly and split the rock sample in half. On the other hand, for isotropic rock, propagation of several fractures occurred and rock samples were split into several parts. Additionally, spalling continuously progressed once the loss of weight exceeded 5% for isotropic rocks because fractures had developed throughout the specimen. This result indicates that freezing-and-thawing cycles at 5% weight loss is assumed to be the spalling initiation. Therefore, we can conclude that the number of freezing-and-thawing cycles to the spalling initiation is the important indicator of the durability evaluation. It was also pointed out that both supply capacity of water to the crack tip and crack growth resistance affect the durability, because the tensile strength divided by the percentage of water absorption is in good correlation with the number of cycles to the spalling initiation. It is concluded that the durability can be easily evaluated by both tensile strength and the percentage of water absorption.
• A new practical method for prediction of geomechanical failure-time

  A. Mufundirwa, Y. Fujii, J. Kodama

  INTERNATIONAL JOURNAL OF ROCK MECHANICS AND MINING SCIENCES 47 7 1079 - 1090 2010年10月 [査読無し][通常論文]
   

  Predicting the failure-time of geo-hazards is an important rock mechanics problem. We first evaluated the validity of the INVerse-velocity (INV) method to predict failure-time of rock mass and landslides. This method utilizes rates of displacement or strain to predict the actual failure-time (T(f)), so the value of total displacement or strain before "failure" is not crucial. Second, we developed a new method for computing failure-time predictions based on the SLOpe (gradient) to predict Tf, termed the SLO method. Finally, a simple conceptualised model representing "safe" and "unsafe" predictions was proposed. To validate these hypotheses, prediction of rock mass failure in the Asamushi and Vaiont landslides (in situ studies) was conducted. Furthermore, laboratory conditions were incorporated into the research, which include predictions using circumferentials train and axial strain from uniaxial compression creep test on Shikotsu welded tuff (SWT), and predictions of failure-time for Inada granite under Brazilian creep tests. It was found that the SLO method is better than the INV method; SLO gave safe predictions in all the cases. In contrast, INV tends to give unsafe predictions(predicted failure-time Tfp > Tf). Our findings reveal that predictions using circumferential strain are better than those made using axial strain for SWT, and notably, given failure with very short tertiary creep, the methods tend to show limited reliability. However, the SLO method could find extensive application in predicting failure-timeofgeo-hazards, for instance, roof wall failure in mines, etc. (c) 2010 Elsevier Ltd. All rights reserved.
• Measurement and interpretation of long-term deformation of a rock slope at the Ikura limestone quarry, Japan

  J. Kodama, E. Nishiyama, K. Kaneko

  INTERNATIONAL JOURNAL OF ROCK MECHANICS AND MINING SCIENCES 46 1 148 - 158 2009年01月 [査読無し][通常論文]
   

  More than 10 years of displacement measurements at the Ikura limestone quarry in Japan have clarified aspects of rock slope deformation arising from excavation in the quarry. Although the cause of most deformations can be explained theoretically, those occurring in a rock slope just behind the Tarumi working face proved perplexing. Contraction continued to occur on the rock slope although excavation of limestone had ceased at this face. The cause of this continuous deformation was evaluated through numerical analysis employed to assess the stability of the rock slope. An automatic 3D mesh generation technique was used to model the complex topography of the quarry resulting from the excavation and a finite element mesh model was rendered for each of the successive excavation stages. Elastic analysis then allowed the resulting rock slope deformation to be predicted. The calculated results reveal that the rock slope continued to deform elastically after excavation had ceased on the Tarumi face and that the on-going excavation at the Kawamukai working face, located 400 m away from the rock slope, was the probable cause. The calculated results using appropriate elastic moduli were in good agreement with measured results. The rock slopes are assessed as stable and the continuous deformation is believed to be elastic. (C) 2008 Elsevier Ltd. All rights reserved.
• 凍結状態にある登別溶結凝灰岩の強度と破壊プロセスに与える温度と載荷速度の影響

  児玉 淳一, 後藤 龍彦, 藤井 義明

  Journal of MMIJ 125 9 472 - 480 2009年 [査読無し][通常論文]
  
• 釧路コールマインに見られる旧坑の閉塞状況と閉塞機構

  石島 洋二, 藤井 義明, 市原 義久, 児玉 淳一

  Journal of MMIJ 124 6/7 435 - 444 The Mining and Materials Processing Institute of Japan 2008年 [査読無し][通常論文]
   

  Kushiro Coal Mine in Kushiro, Japan is now excavating coal seams at a shallower level than before. Approximately 100 old workings, which were excavated about 50 years ago, were observed at either longwall coal faces or sidewalls of roadways. Most of them were completely closed with a few exceptions, which were in open condition without severe deformation. Two thirds of the observed old workings were closed mainly by roof sagging. The sagged roofs were either deflected or plugged in. Development of the tension cracks were observed in the deflected roof. One third of the old workings were closed mainly by floor heaving, mostly accompanied by the severe deflection.
  Complete closure of the old workings can be attributed to the following two reasons: One is rock stress of considerable magnitude composed from the initial one and the induced one due to mining. Another is weakening of the sedimentary rocks surrounding the opening due to increase of the water content brought mainly by the supply of water detached from the injected filling material with high water content. It is certain that the two mechanisms work simultaneously to the closure of the old workings, but the latter is considered to be prior to the former in its effect.
• 接線ヤング率法の三つの岩種に対する適用性と同方法における封圧の影響

  藤井 義明, 大高 憲道, 中川 嘉文, 児玉 淳一

  Journal of MMIJ 124 2 120 - 128 The Mining and Materials Processing Institute of Japan 2008年 [査読無し][通常論文]
   

  The tangent modulus method was applied to pre-loaded cylindrical specimens of Shikotsu welded tuff, Inada granite and Kimachi sandstone. It was clarified that the tangent modulus method could be applied to the rocks. A positive correlation was observed between the preloading duration and the maximum delay time at which the preloaded stress was determined with the error less than 20% for Shikotsu welded tuff and Inada granite although the correlation was not confirmed for Kimachi sandstone due to small number of specimens. The confirmed maximum delay time for each rock was 42 days for Shikotsu welded tuff, 21 days for Inada granite and 28 days for Kimachi sandstone based on clip gage.
  The stress at bending point in uniaxial cyclic loading for triaxially pre-loaded Kimachi sandstone decreased as confining pressure in the preloading increased. Kimachi sandstone and Shirahama sandstone were triaxially preloaded and triaxially cyclic loaded under decreased or increased confining pressure. The stress at bending point decreased with decrease of confining pressure for Shirahama sandstone. No apparent change was observed for Kimachi sandstone. Bending points were not observed for Shirahama sandstone under increased confining pressure. On the other hand, the stress at bending point decreased with increase of confining pressure for Kimachi sandtsone.
  The physical phenomena utilized to detect stress memory in tangent modulus method was explained based on a model which consisted of two springs and a slider. One spring represents the elasticity of rock. Another spring and the slider are connected in parallel and represent inelasticity due to irreversible closure of voids. Decrease of tangent modulus at the preloaded stress was well simulated by the model.
• 採掘変形計測による広域応力と地盤ヤング率の評価

  西山 えるむ, 宮本 高充, 児玉 淳一, 川崎 了, 金子 勝比古

  Journal of MMIJ 124 9 570 - 575 The Mining and Materials Processing Institute of Japan 2008年 [査読無し][通常論文]
   

  A method to evaluate the regional stresses and the Young's modulus by analyzing mining induced deformation of the ground is proposed.
  Mining induced deformation is interpreted as the deformation due to the geometrical change of the ground surface caused by mine activity and it is classified in two types, i.e., the displacement increment induced by gravity and that by the horizontal regional strain. It is pointed out that both the regional strain and Young's modulus can be estimated by analyzing the mining induced deformation, because the displacement induced by the regional strain is independent of the Young's modulus and the displacement induced by the gravity is inversely proportional to the Young's modulus.
  The relative displacement due to mine excavation in Torigatayama mine were measured by GPS (Global Positioning System) and the regional stress state and Young's modulus were estimated by a back-analysis using three dimensional finite element method. It is shown that the maximum principal direction of regional stresses is almost NE-SW and Young's modulus of the ground is 3 to 6GPa in the present field.
• 凍結状態にある岩石の強度と変形・破壊挙動

  児玉 淳一, 後藤 龍彦, 藤井 義明

  Journal of MMIJ 124 12 733 - 740 The Mining and Materials Processing Institute of Japan 2008年 [査読無し][通常論文]
   

  Understanding mechanical behavior of frozen rocks is useful for evaluating the stability of rock slopes in cold regions. In this study, uniaxial compression tests and Brazilian tests were carried out on frozen rock specimens of welded tuff and andesite under -20°C temperature. The fracture process was examined by observing deformation behaviors and AE activities. Effects of water saturation degree on strength and deformability were also investigated. The main results are as follows.
  1) The fracture process of the frozen rock was similar to that of non-frozen rock and was divided into the following regions. (I) Closure of cracks and pores. (II) Elastic deformation. (III) Fracture initiation and stable fracture propagation. (IV) Unstable fracture propagation. Also, stress levels at the beginning of the region (III) increased with the degree of water saturation.
  2) Both strength and strain at peak stress increased as the degree of water saturation increased. The relations between them were able to be approximated by a straight line. Brittleness of rocks decreased with the degree of water saturation since indirect tensile strength was more sensitive to the degree of water saturation than uniaxial compressive strength.
  3) The mechanical effect of frozen pore water was considered with an inclusion model. The model predicted the observed phenomenon. Namely, increment in fracture initiation stress, due to frozen pore water in uniaxial tension, was always higher than that in uniaxial compression. The increase in strength was thought to result from relaxation of stress concentration around pores.
• Durability characteristics of some assorted rocks

  GP Dhakal, J Kodama, T Yoneda, KM Neaupane, T Goto

  JOURNAL OF COLD REGIONS ENGINEERING 18 3 110 - 122 2004年09月 [査読無し][通常論文]
   

  Durability characteristics of some argillaceous clastic rocks from cold regions are investigated. Two sets of experiments, namely slake durability (wet-dry) and freeze-thaw tests, were conducted on welded tuff, carbonates (limestone and dolomite), sandstone, and schist samples collected from northern parts of Japan and from the higher Himalayas of Nepal. The slaking tests were performed in pure water and seawater as well as in aqueous Solution of different salinity. A tendency to decrease in slake durability with an increase in porosity is observed. The results reveal that the stake durability of a rock increases with an increase in the concentration of salt in water. Freeze-thaw experiments conducted on welded tuff and schist reveal that crack initiates earlier but extends slower in schist than in welded tuff and that the tuff deteriorates and wears faster than the schist.
• 井倉鉱山における残壁の長期変形計測とその解析

  児玉 淳一, 金子 勝比古, 都築 雅年, 西山 えるむ

  資源と素材 120 4 5,182-189 - 189 The Mining and Materials Processing Institute of Japan 2004年 [査読無し][通常論文]
   

  Several characteristics of deformation of a rock slope due to excavation are clarified through a displacement measurement on Ikura limestone quarry for more than ten years. However, some causes of measured deformation have been still unknown. The rock slope behind the Tarumi face showed continuous contraction while the excavation was interrupted at this face. In this study, a cause of the continuous deformation was studied to evaluate stability of the rock slope by means of numerical analysis. Complex topography of the mining area on Ikura limestone quarry was modeled in three dimensions at several excavation stages. Then, an elastic analysis was carried out to estimate the deformation of the rock slope due to excavation in the whole mining area. Through the analysis, it was found that the rock slope could deform elastically while the excavation was interrupted at the Tarumi face. It was estimated to contract gradually due to progressive excavation at the Kawamukai face, which was located at 400m away from the rock slope. Analyzed results were consistent with the observed results under an adequate elastic constant. Therefore, this rock slope was evaluated to be stable because the continuous deformation caused by the excavation was elastic.
• 引張亀裂面の形態評価に関する実験的研究

  羅 紹河, 後藤 龍彦, 児玉 淳一

  Journal of MMIJ 120 10/11 569 - 576 The Mining and Materials Processing Institute of Japan 2004年 [査読無し][通常論文]
   

  Tensile fractures were nucleated and developed from a borehole, which was drilled at the center of a block of granite with two types of boundary conditions. Samples were then prepared from the blocks before the fracture penetrated throughout the block, in order to clarify the fracture surfaces in the original condition. Next, cross sectional photographs of the samples containing the fracture were taken by holding the fracture surfaces in the original opening condition. Based on the photographs, coordinate values of upper and lower boundaries of fracture profiles were measured at a regular interval. Moreover, fracture apertures, fracture angle, and closing direction of fracture surfaces were estimated at each local part of both fracture surfaces.
  It was found that the fracture angle of the fracture surfaces tended to gradually decrease from the wall of the borehole to the fracture front. This result reveals that the upper and lower fracture surfaces can be assumed to be almost the same in direction with regards to approaching the fracture front.
  Two patterns of the fracture propagation could be extracted from a distribution of closing direction vectors of the fracture surfaces. One is a linear pattern, and the other is a radial pattern. These patterns are similar in structure to a tree spreading out its branches. It was considered that such a structure is closely related to the fractal behavior for roughness evaluated by fracture profiles.
  The aperture tended to gradually decrease with a distance from the wall of the borehole. Its decreasing direction harmonized well with the direction of the fracture propagation. It was recognized that macroscopic distribution of apertures was strongly related to the distribution of tensile stress induced in samples before the occurrence of fractures.
• 自然乾燥状態および湿潤状態における登別溶結凝灰岩のクリープ変形とクリープ寿命

  児玉 淳一, 後藤 龍彦, 藤井 義明, 吉田 豊, 板倉 賢一

  資源と素材 117 9 718 - 724 The Mining and Materials Processing Institute of Japan 2001年 [査読無し][通常論文]
   

  Not only axial strain but also lateral strain were measured during creep tests on Noboribetsu welded tuff under air-dried and water-saturated conditions in which the water contents of specimens were regulated about 0.3% and 17%, respectively. Creep rupture strength under water-saturated condition was smaller than that under air-dried condition. The difference in them was comparable to that in uniaxial compressive strength under both conditions. The axial and lateral strain rates decreased linearly with time in a log-log plot in the primary stage. They increased until a rupture occurs after the strain rates had reached the minimum magnitude. Creep failure time tended to increase as the "decrease rates of the strain rates" in the primary stage increased. Creep failure time and the life after the minimum strain rate increased as the minimum magnitude in the strain rates decreased. In the tertiary stage, the strain rates were inversely proportional to residual life. These relationships were represented by the same curves regardless of the water content. Therefore, the creep failure time would be successfully estimated from the behaviors of either axial or lateral strain rate regardless of the water content by using the experimental results. Thin sections of the specimens that had experienced various levels of the creep deformation were prepared and observed under a microscope. Nucleation of cracks and pores that distributed along the loading axis in the matrix were observed for specimens that had been just before the rupture.
• Estimation of the Fatigue Strength of Granite Subjected to Long-period Cyclic Loading

  児玉 淳一, 石塚 与志雄, 安部 透, 石島 洋二, 後藤 龍彦

  Journal of the Mining and Materials Processing Institute of Japan 116 2 111 - 118 The Mining and Materials Processing Institute of Japan 2000年 [査読無し][通常論文]
   

  The effects of excitation frequency on fatigue life and fatigue damage were investigated by carrying out a series of cyclic loading tests at high stress levels on Inada granite. An attempt was made to estimate fatigue strength under long-period loading based on the experimental results. The amount of fatigue damage per cycle and fatigue life decreased with increases in the excitation frequency at the same maximum stress. On the other hand, they did not depend on the excitation frequency between 2.5 × 10 ^{- 4} Hz and 0.5 Hz when the same maximum stress ratio, which was normalized by the static strength under a strain rate corresponding to the excitation frequency, was applied. Cyclic fatigue tests at the frequency of 0.5 Hz were performed under several stress ratios. It was clarified that : (1) there is no fatigue limit within 4 × 10⁴ cycles of loading, (2) the relationship between stress ratio S and fatigue life N_f can be represented by S = A - B log N_f (S - N_f curve), (3) fatigue strength increases with increases in confining pressure, and (4) fatigue strength decreases in the presence of water. Estimation of fatigue strength under long-period loading might be possible using both the S - N_f curve and the relationship between static strength and strain rate.
• Circumferential Strain Behavior During Creep Tests of Brittle Rocks

  Int. J. Rock Mech. Min. Sci. 36 3 323 - 337 1999年 [査読無し][通常論文]
  
• 大気ガス濃度計測システム －CO2レーザによる光音響変換ガス濃度測定システムについて（第3報）－

  吉田 豊, 西辻 昭, 後藤 龍彦, 板倉 賢一, 児玉 淳一

  Journal of MMIJ 115 2 77 - 82 The Mining and Materials Processing Institute of Japan 1999年 [査読無し][通常論文]
   

  In order to measure concentration of some kinds of gases flowing or emitting abruptly in underground space such as roadway in mine and tunnels, we have been studying a continuous and real time measurement system for gas concentration by means of a photoacoustic effect. In the previous papers, a calibration system and procedure to obtain the characteristics of photoacoustic signals, which was the relationships between gas concentration and photoacoustic intensity when CO2 laser was used, were examined. In this paper, we describe development procss and expermental results of new measurement system for atmospheric gas concentration changing with time. On the development process, the cooling system for laser discharge tube was converted from water circulation type to air circulation or electronic element cooling type to achieve the portability. Also, the doubletube type photoacoustic cell was improved to draw air in it for the continuous measurement of photoacoustic signals. Using the new systems, laboratory experiments were carried out to obtain the characteristics of the photoacoustic signals, and to compare the measurement accuracy of this system to the previous system. Consequently, we confirmed the availability of this new system in time response and in quantitative monitoring by the continuous measurement of CO2 gas in the atmosphere.
• Examination of a rock failure criterion based on circumferential tensile strain

  Y Fujii, T Kiyama, Y Ishijima, J Kodama

  PURE AND APPLIED GEOPHYSICS 152 3 551 - 577 1998年10月 [査読無し][通常論文]
   

  Uniaxial compression, triaxial compression and Brazialian tests were conducted on several kinds of rock, with particular attention directed to the principal tensile strain. In this paper we aim to clarify the effects of the experimental environment-such as confining pressure, loading rate, water content and anisotropy-on the critical tensile strain, i.e., the measured principal tensile strain at peak load. It was determined that the chain-type extensometer is a most suitable method for measuring the critical tensile strain in uniaxial compression tests. It is also shown that the paper-based strain gage, whose effective length is less than or equal to a tenth of the specimen's diameter and glued on with a rubber-type adhesive, can be effectively used in the Brazilian tests. The effect of confining pressure P-C on the critical tensile strain epsilon(TC) in the brittle failure region was between -0.02 x 10(-10) Pa-1 and 0.77 x 10(-10) Pa-1. This pressure sensitivity is small compared to the critical tensile strain values of around -0.5 x 10(-2). The strain rate sensitivities partial derivative epsilon(TC)/partial derivative{log(d\epsilon\/dt)} were observed in the same way as the strength constants in other failure criteria. They were found to be from -0.10 x 10(-3) to -0.52 x 10-3 per order of magnitude in strain rate in the triaxial tests. The average magnitude of the critical tensile strain epsilon(TC) increased due to the presence of water by 4% to 20% for some rocks, and decreased by 22% for sandstone. It can at least be said that the critical tensile strain is less sensitive to water content than the uniaxial compressive strength under the experimental conditions reported here. An obvious anisotropy was observed in the P-wave velocity and in the uniaxial compressive strength of Pombetsu sandstone. It was not observed, however, in the critical tensile strain, although the data do show some variation. A "tensiie strain criterion" was proposed, based on the above experimental results. This criterion signifies that stress begins to drop when the principal tensile strain reaches the critical tensile strain. The criterion is limited to use within the brittle failure region. The critical tensile strain contains an inelastic strain component as well as an elastic one. It is affected by the strain rate, however, it is relatively insensitive to the confining pressure, the presence of water and anisotropy.
• AE震源分布のフラクタル構造に基づいた岩石内き裂系のモデル化に関する研究

  板倉 賢一, 渡部 義範, 佐藤 一彦, 後藤 龍彦, 児玉 淳一, 吉田 豊

  Journal of MMIJ 114 12 918 - 924 The Mining and Materials Processing Institute of Japan 1998年 [査読無し][通常論文]
   

  In underground construction it is important to obtain a discontinuities' model of rocks for simulations to evaluate rock stability around the working space and fluid flow in the rocks. In this study, an uniaxial compression test on a prism-shaped specimen of granite was conducted to develop a more feasible modeling method of cracks in rocks based on AE (acoustic emission) monitoring data and the fractal properties of the AE source distribution. 1. From this experiment, it was found that the AE source distribution was fractal and that the relationship between amplitude and frequency of AE was also fractal. 2. Crack distributions in the specimen and on the surface were both fractal. 3. A 3-D crack distribution model was constructed using AE monitoring data obtained from the experiment. In this model, the crack was described by a disk, and the fractal dimension of sectional lines that appeared on the surface of a specimen was adjusted to coincide with the dimension of lineaments extracted from a real crack image of the same surface of the specimen by correcting the AE parameters. That is, the relative AE energy for each event were altered iteratively until both fractal dimensions were matched. It is thought that this new modeling method for cracks in rocks can be directly applied to field studies of underground construction in the future.
• 登別溶結凝灰岩の力学的挙動に与える間隙流体圧とひずみ速度の影響

  後藤 龍彦, 児玉 淳一, 吉田 豊, 板倉 賢一

  Journal of MMIJ 113 4 227 - 232 資源・素材学会 1997年 [査読無し][通常論文]
  
• 二重管方式光音響共鳴セルの試作 －CO2レーザによる光音響変換ガス濃度測定システムについて（第2報）－

  吉田 豊, 西辻 昭, 後藤 龍彦, 板倉 賢一, 児玉 淳一

  Journal of MMIJ 113 2 127 - 132 資源・素材学会 1997年 [査読無し][通常論文]
  
• 封圧下における稲田花崗岩の疲労特性

  資源と素材 113 4 241 - 246 1997年 [査読無し][通常論文]
  
• Application of the Ultrasonic Propagation Time of a Core Sample for Stress Measurement of Underground Rocks

  後藤 龍彦, 児玉 淳一, 板倉 賢一, 吉田 豊

  Journal of the Mining and Materials Processing of Japan 113 8 593 - 599 資源・素材学会 1997年 [査読無し][通常論文]
  
• 長壁式採炭に伴う切羽周辺の地圧変化に関する地層模型試験

  後藤 龍彦, 児玉 淳一, 吉田 豊, 板倉 賢一, 藤井 義明

  Journal of MMIJ 112 7 439 - 444 資源・素材学会 1996年 [査読無し][通常論文]
  
• 封圧下における岩石の破壊特性に及ぼす間隙ガス圧効果

  後藤 龍彦, 児玉 淳一, 吉田 豊, 板倉 賢一

  Journal of MMIJ 112 1 11 - 16 The Mining and Materials Processing Institute of Japan 1996年 [査読無し][通常論文]
   

  The effect of pore gas pressure on the mechanical behavior of rocks has been investigated in order to confirm the validity of the effective confining pressure law among rocks. The triaxial compression tests of Noboribetsu welded tuff, Horonai sandstone (A), (B), Akabira sandstone and Akiyoshi marble were carried out with the strain rate 1.3 × 10^-4/sec for confining and pore gas pressure combined with a conventional hydraulic testing machine. The stress strain curves of five kinds of rocks were determined under the condition of confining and pore gas pressure extending up to 50 MPa.
  The experiments show that the effective confining pressure law was valid for more porous and permeable rocks such as Noboribetsu welded tuff, Horonai sandstone (A), (B) and Akabira sandstone but Akiyoshi marble was not possible to adopt this law.
  The mechanical behavior of rocks whose pore are not fully saturated with gas pressure seems to largely depend on magnitude of the confining pressure acting on specimens.
• 若鍋層頁岩の浸水，湿潤に伴うＡＥ活動と２，３の力学的特性について

  後藤 龍彦, 板倉 賢一, 中田 雅夫, 児玉 淳一, 吉田 豊

  Jounal of MMIJ 111 5 295 - 300 資源・素材学会 1995年 [査読無し][通常論文]
  
• 太平洋炭砿における長壁式採炭切羽周辺の岩盤挙動に関する計測事例

  後藤 龍彦, 松本 裕之, 藤井 義明, 児玉 淳一, 佐藤 干城, 出口 剛太

  Journal of MMIJ 111 4 213 - 218 資源・素材学会 1995年 [査読無し][通常論文]
  
• 一定応力および繰返し応力下における花崗岩内のクラック伸長の観察

  児玉淳一, 石島洋二, 後藤龍彦

  資源と素材 111 12 841 - 847 資源・素材学会 1995年 [査読無し][通常論文]
  
• 微視構造モデルによる花崗岩の強度特性の時間依存性に関する理論的検討

  児玉 淳一, 石塚 与志雄, 安部 透, 石島 洋二

  資源と素材 110 3 195 - 200 資源・素材学会 1994年 [査読無し][通常論文]
  
• 赤平炭を用いた室内試験からの考察 －坑道引立面付近の炭層状況と破壊挙動に関する研究－

  後藤 龍彦, 藤井 義明, 佐藤 干城, 児玉 淳一

  Journal of MMIJ 110 15 1227 - 1232 資源・素材学会 1994年 [査読無し][通常論文]
  
• 間隙ガス圧下における石炭の力学的挙動

  後藤 龍彦, 佐藤 干城, 児玉 淳一, 出口 剛太

  Jornal od MMIJ 110 8 667 - 672 1994年 [査読無し][通常論文]
  
• 一軸圧縮下における花崗岩の疲労・クリープ特性と長期強度

  児玉淳一, 石塚与志雄, 安部透, 石島洋二

  Journal of MMIJ 108 3 182 - 186 1992年 [査読無し][通常論文]
  

書籍

• 残壁ハンドブック

  丸善 2005年

受賞

• 1999年 資源・素材学会奨励賞
  

共同研究・競争的資金等の研究課題

• 凍結融解現象を考慮した岩盤斜面の安定性評価

教育活動情報

主要な担当授業

大学運営

委員歴

• 2004年 - 2006年   資源・素材学会   岩盤斜面工学小委員会幹事   資源・素材学会
• 2004年 - 2006年   資源・素材学会   北海道支部幹事長   資源・素材学会
• 1997年   資源・素材学会   岩盤工学部門委員会委員   資源・素材学会