論文 - 京川 裕之
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Simple modelling of stress-strain behaviour of unsaturated soils 査読あり
M. Kikumoto, H. Kyokawa, T. Nakai
14th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering 2011年
掲載種別：研究論文（国際会議プロシーディングス）
A simple constitutive model taking account of the necessary features of unsaturated soils is proposed by extending an elastoplastic model for saturated soils. The proposed model is formulated using the Bishop's effective stress and the critical state friction angle is thus assumed to be constant. In the model, the decrease (or increase) in the degree of saturation is linked with upward (or downward) movement of normally consolidation line in the plane of mean effective stress and void ratio, by which the typical volumetric behaviours of unsaturated soils are properly described. A simple method for extending a classical water characteristics curve assuming a unique relationship between suction and degree of saturation to incorporate the effects of hydraulic hysteresis and density is also proposed. In this paper, mechanisms of hydraulic collapse and compaction of soils are discussed through a series of simulations by the proposed model.
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New approach for modeling time-dependent behavior of geomaterials 査読あり
T. Nakai, H. M. Shahin, M. Kikumoto, H. Kyokawa, F. Zhang, M. M. Farias
Computational Geomechanics, COMGEO II - Proceedings of the 2nd International Symposium on Computational Geomechanics 49 - 62 2011年
掲載種別：研究論文（国際会議プロシーディングス）
A simple method to describe time-dependent behavior for various kinds of soils is presented. The model is formulated not using usual viscoplastic theories but utilizing the subloading surface concept by Hashiguchi (1980) and paying attention to the experimental results, which show that the normal consolidation line (NCL) and the critical state line (CSL) on the e - lnσ plane shift depending on the strain rate. The formulation is first explained in one-dimensional conditions in order to understand the method easily. After that, using the tij concept proposed by Nakai and Mihara (1984), the one-dimensional model is extended to a three-dimensional one. The validity of the present model is verified using various kinds of simulations of time-dependent behavior in both conditions - e.g., onedimensional compression tests under different strain rate, oedometer tests including secondary consolidation, creep and stress relaxation tests, constant strain rate triaxial tests and others.
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Modeling of one-dimensional consolidation behavior for clays 査読あり
T. Nakai, H. M. Shahin, H. Kyokawa, Y. Miyahara
14th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering 2011年
掲載種別：研究論文（国際会議プロシーディングス）
A simple method to describe stress-strain behavior of structured soils under normally and over consolidated states in one-dimensional stress condition is presented by introducing a state variable (ρ) to represent the influence of density and another state valuable (ω) which represents the imaginary increase of density by boding effect. Then, another state variable (ψ) is introduced to describe the time dependent behavior, the temperature dependent behavior, the effect of saturation and others. Here, the state valuable (ψ) has a function which shifts the normally consolidation line (NCL) due to the strain rate, temperature, saturation and others. Although the models are formulated in one-dimensional condition in this paper, it is possible to extend them to three-dimensional ones using t ij concept, easily.
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Bridges washed away by tunami in Minamisanriku, Miyagi Prefecture in the March 11th 2011 Great East Japan Earthquake (特集 耐震構造学研究グループ(ERS) 東日本大震災 : 巨大地震の脅威と教訓) 査読あり
AGLIPAY Mary Roxanne I., KESHAB Sharma, KYOKAWA Hiroyuki, KONAGAI Kazuo
生産研究 63 ( 6 ) 723 - 727 2011年
記述言語：英語 出版者・発行元：東京大学生産技術研究所
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A simple method to consider density and bonding effects in modeling of geomaterials 査読あり
Teruo Nakai, Mamoru Kikumoto, Hiroyuki Kyokawa, Hassain M. Shahin, Feng Zhang
Springer Series in Geomechanics and Geoengineering 5 91 - 111 2011年
掲載種別：研究論文（学術雑誌）
A simple method to describe stress-strain behavior of structured soils under normally and over-consolidated states in one-dimensional stress condition is first presented by introducing a state variable to represent the influence of density. To describe the one-dimensional stress-strain behavior of structured soils, attention is focused on the density and the bonding as the main factors that affect a structured soil, because it can be considered that the soil skeleton structure in a state which is looser than that of a normally consolidated soil is formed by bonding effects. The extension from one-dimensional model to three-dimensional model can be done only by defining the yield function using the invariants of modified stress 'tij' instead of one-dimensional stress 'σ' and assuming the flow rule in modified stress space tij. © Springer-Verlag Berlin Heidelberg 2011.
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Simple modeling of stress-strain relation for unsaturated soil 査読あり
H. Kyokawa, M. Kikumoto, T. Nakai, H. Shahin
Geotechnical Special Publication ( 202 GSP ) 17 - 25 2010年
掲載種別：研究論文（国際会議プロシーディングス）
Though stress-strain characteristics of unsaturated soils are complicated and rather different from those of saturated soils, it should be described properly by a constitutive model for soils because soil usually stays under an unsaturated condition in actual field. In the current study, a simple elastoplastic model for saturated soil is extended to one applicable to unsaturated soils. The proposed model is formulated using the Bishop's effective stress and the residual strength is, therefore, assumed to be constant. In the proposed model, the decrease (or increase) in the degree of saturation is linked with upward (or downward) movement of normally consolidated line in the compression plane of mean effective stress and void ratio, by which the typical volumetric and distortional behaviors of unsaturated soils are properly described. In addition, a simple method to extend classical water retention curves such as van Genuchten's equation to be able to incorporate the influences of suction histories and density is proposed and applied to the proposed model. In the present paper, the outline of the proposed model is explained and applicability of the model is discussed through typical results of simulations. © 2010 ASCE.
DOI： 10.1061/41103(376)3
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修正応力を用いた等方硬化モデルによる誘導異方性の表現 査読あり
京川 裕之, 菊本 統, 中井 照夫
地盤工学ジャーナル 5 ( 4 ) 533 - 544 2010年
記述言語：日本語 出版者・発行元：公益社団法人 地盤工学会
実地盤内の応力状態は必ずしも三軸条件（軸対称応力）ではなく，相異なる三主応力（真三軸条件）下で主応力方向が回転しながらランダムに変化する。このような応力変化を受けると土の粒子配列は複雑に変化するため，異方的な変形特性，すなわち誘導異方性が現れる。このような誘導異方性は任意の応力変化を受ける実地盤の応答を予測する上で無視できない性質といえる。従来，誘導異方性は移動硬化則や回転硬化則により記述されてきたが，いずれの方法も複雑で，用いられる内部変数や構成パラメータの物理的な意味合いも明確でない。本研究では誘導異方性の影響は中間主応力の影響とその本質は同じと考え，中間主応力の影響を適切に考慮した修正応力<i>t<sub>ij</sub></i>を拡張した新たな修正応力<i>t<sub>ij</sub></i><sup>*</sup>を提案する。修正応力<i>t<sub>ij</sub></i><sup>*</sup>に基づいて定式化した提案モデルは，等方硬化モデルでありながら，実測値に見られる中間主応力の影響ならびに応力履歴による複雑な剛性・ひずみ増分方向変化を統一的かつ適切に表現できる。
DOI： 10.3208/jgs.5.533
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A SIMPLE DESCRIPTION OF THE STRESS-STRAIN AND HYDRAULIC BEHAVIOURS OF UNSATURATED SOIL 査読あり
H. Kyokawa, M. Kikumoto, Teruo Nakai
RECENT DEVELOPMENTS OF GEOTECHNICAL ENGINEERING 74 - 81 2010年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：JAPANESE GEOTECHNICAL SOC
Stress-strain behaviour of unsaturated soils is rather complex and quite different from that of saturated soils. However, it should be described properly by a constitutive model for soils because soil usually lies under an unsaturated state in the actual field. In the current study, a simple elastoplastic model for saturated soil is extended to one considering the necessary characteristics of unsaturated soils. The proposed model is formulated using the Bishop's effective stress and the residual strength is, therefore, assumed to be constant. In order to describe the behaviour of unsaturated soils, the decrease (or increase) in the degree of saturation is linked with upward (or downward) movement of normally consolidated line in the compression plane of mean effective stress and void ratio, by which the typical volumetric behaviours of unsaturated soils can be properly described. In addition, a simple method to extend classical water retention curves such as van Genuchten's equation is proposed in order to incorporate the influences of suction histories and density and it is applied to the proposed model. Because the volumetric behaviours of unsaturated soils such as consolidation and collapse behaviours are mainly focused on in the present paper, a simplified one-dimensional formulation of the elastoplastic constitutive model is explained. The validity of the proposed model is discussed through typical results of simulations.
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MODELING OF TIME-DEPENDENT BEHAVIOR OF CLAY IN ONE-DIMENSIONAL CONSOLIDATION 査読あり
H. M. Shahin, T. Nakai, M. Kikumoto, H. Kyokawa, Y. Miyahara
RECENT DEVELOPMENTS OF GEOTECHNICAL ENGINEERING 54 - 61 2010年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：JAPANESE GEOTECHNICAL SOC
One-dimensional consolidation tests on clay have been performed using a one-dimensional model which can consider the effects of density, bonding and time. The model can explain strain rate effect, stress relaxation characteristics and creep characteristics of soils comprehensively without fitting the model for a particular phenomenon. The model can also describe other characteristics of soils such as secondary compression, delayed consolidation and consolidation characteristics of naturally deposited soils. Here, consolidation behavior of clay has been investigated varying the density of soil having different states of bonding. Varying the thickness of soil samples, the dependency of the sample height on the consolidation behavior has been checked as well. It is found that the model can explain well the behavior of secondary consolidation of naturally consolidated soil, overconsolidated soil and structured soil.
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Elastoplastic modeling of geomaterials considering the influence of density and bonding 査読あり
T. Nakai, H. Kyokawa, M. Kikumoto, H. M. Shahin, F. Zhang
Prediction and Simulation Methods for Geohazard Mitigation 367 - 373 2009年01月
掲載種別：論文集(書籍)内論文
© 2009 Taylor & Francis Group, London. To understand easily the method for modeling the behavior of structured soils, one-dimensional description of elastoplastic behavior is firstly shown, and then it is extended to a constitutive model in general three-dimensional stress conditions. To describe the stress-strain behavior of structured soils, attention is focused on the density and the bonding as the main factors that affect a structured soil, because it can be considered that the soil skeleton structure in a state, which is looser than that of a normally consolidated soil, is formed by bonding effects including interlocking between soil particles and others. The extension from one-dimensional model to three-dimensional model can be done only by defining the yield function using the invariants of modified stress ‘tij’ instead of one-dimensional stress ‘σ’ and assuming the flow rule in modified stress space tij.
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A unified method to describe the influences of intermediate principal stress and stress history in constitutive modelling 査読あり
M. Kikumoto, T. Nakai, H. Kyokawa, F. Zhang, H. M. Shahin
Geotechnics of Soft Soils - Focus on Ground Improvement - Proceedings of the 2nd International Workshop on Geotechnics of Soft Soils 151 - 157 2009年
掲載種別：研究論文（国際会議プロシーディングス）
A simple and unified method for considering the influences of the intermediate principal stress and the stress histories on the deformation and the strength of soils, which obeys isotropic hardening rule in modified stress space, is proposed. The concept of the modified stress tij, which was proposed before by our group to describe the influence of the intermediate principal stress, is extended to a new stress tensor tij* to consider the fabric change of soils due to the variations of the intermediate principal stress and the stress histories. The evolution rule of tij* is established referring to past experimental evidences. In this paper, the modified stress tij* is applied to the isotropic hardening elastoplastic model named subloading tij model. The proposed model is verified by comparing the calculated results with the experimental results of true triaxial tests and directional shear tests on medium dense sand. © 2009 Taylor & Francis Group.
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New description of stress-induced anisotropy using modified stress 査読あり
M. Kikumoto, T. Nakai, H. Kyokawa
Proceedings of the 17th International Conference on Soil Mechanics and Geotechnical Engineering: The Academia and Practice of Geotechnical Engineering 1 550 - 553 2009年
掲載種別：研究論文（国際会議プロシーディングス）
A simple and comprehensive method for describing the influences of the intermediate principal stress σ 2 and the stress histories on the deformation and the strength of soils, which assumes associated flow rule and obeys isotropic hardening rule in modified stress space, is proposed. The concept of the modified stress t ij, which was proposed to describe the influence of σ 2, is extended to the proposed modified stress tensor t ij* to consider the fabric change of soils due to the stress histories as well as the variation of σ 2. In this paper, the modified stress t ij* is applied to an elastoplastic model named subloading t ij model. The proposed model is verified by comparing the calculated results with the experimental results on sand. © 2009 IOS Press.
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Modelling the influence of density and bonding on geomaterials 査読あり
T. Nakai, F. Zhang, H. Kyokawa, M. Kikumoto, H. M. Shahin
Geotechnics of Soft Soils - Focus on Ground Improvement - Proceedings of the 2nd International Workshop on Geotechnics of Soft Soils 65 - 76 2009年
掲載種別：研究論文（国際会議プロシーディングス）
A simple method to describe stress-strain behavior of structured soils under normally and over consolidated states in three-dimensional stress condition is presented. Based on an idea that structured soils can be made due to a kind of bonding effects between soil particles, a simple elastoplastic model is formulated by extending subloading tij model developed before. First, a new interpretation of subloading surface concept for describing the influence of density and/or confining pressure is described. Then, a method to take into consideration the effect of bonding on the soil behavior in constitutive modeling is developed. By introducing this method for considering bonding to the subloading tij model, the stress-strain behavior of structured soils is described. The validity of the proposed model is confirmed by numerical simulation of oedometer tests and undrained shear tests on structured clay. © 2009 Taylor & Francis Group.
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地盤材料の諸特性の簡単且つ統一的なモデリング-密度,ボンディング,時間効果特性を中心として- 査読あり
京川 裕之
応用力学論文集 12 371 - 382 2009年
掲載種別：研究論文（学術雑誌）
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等方硬化モデルで誘導異方性を考慮する方法 査読あり
菊本 統, 中井 照夫, 張 鋒, 京川 裕之, 石原 隆寛
理論応用力学講演会 講演論文集 57 ( 0 ) 156 - 156 2008年
記述言語：日本語 出版者・発行元：日本学術会議 「機械工学委員会・土木工学・建築学委員会合同IUTAM分科会」
中間主応力と応力履歴の影響(すなわち誘導異方性)は，地盤の挙動予測を行う上で考慮すべき土の力学特性である．従来のモデルでこれらを考慮するには，通常の応力空間で移動(回転)硬化則を仮定し，さらに偏差応力面での降伏面の形状を歪ませる(もしくは中間主応力に応じて材料強度を変化させる)必要があった．しかし，このような方法を用いなくても中間主応力と応力履歴の影響を反映した構造テンソルで応力を変換して用いれば誘導異方性は表現できる．本研究では，通常の応力の代わりに修正応力を用いるだけで，誘導異方性を一般性が保証され簡単な形で表せる等方硬化モデルで記述する新しい方法を提案する．
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Description of induced anisotropy of soils using isotropic hardening rule in modified stress space 査読あり
M. Kikumoto, H. Kyokawa, T. Nakai, F. Zhang, M. Hinokio
Proceedings of the 10th International Symposium on Numerical Models in Geomechanics NUMOG 10 - Numerical Models in Geomechanics NUMOG 10 85 - 91 2007年
掲載種別：研究論文（国際会議プロシーディングス）
A simple method for describing the stress-induced anisotropy of soils, which obey isotropic hardening rule in modified stress space, is proposed. The concept of the modified stress tij, by which the influence of the intermediate principal stress on the deformation and the strength of soils is properly considered, has been proposed before. In the present study, this concept is extended and a new stress measure t*ij is incorporated to be able to consider the fabric change of soils due to variation of stress histories, namely, induced anisotropy. The evolution rule of t*ij is provided referring to the existing experimental evidence. Then, the modified stress t*ij is applied to an isotropic hardening elastoplastic model named Subloading tij model as an example. The model is verified by experimental results in isotropic and anisotropic compression and shear tests with different stress histories under triaxial conditions. © 2007 Taylor & Francis Group.
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A simple modeling of structured soils 査読あり
T. Nakai, F. Zhang, H. Kyokawa, M. Kikumoto
NEW FRONTIERS IN CHINESE AND JAPANESE GEOTECHNIQUES 435 - 447 2007年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：CHINA COMMUNICATIONS PRESS
A simple method to describe stress-strain behavior of structured soils under normally and over consolidated states in general stress systems is presented. Based on an idea that structured soils can be made due to a kind of bonding effects between soil particles, a simple elastoplastic model is formulated by extending subloading t(ij) model (Nakai and Hinokio, 2004). Firstly, a new interpretation of subloading surface concept for describing the influence of density and/or confining pressure is shown. Secondly a method to take into consideration the effect of bonding on the soil behavior in constitutive modeling is developed. By introducing this method for considering bonding to the subloading t(ij) model, the stress-strain behavior of structured soils can be described. The validity of the proposed model is checked through numerical simulation of oedometer tests and undrained shear tests on structured clays. An interpretation for super/subloading surface concept to describe structured soil by Asaoka et al. (1998) is also given, and the similarities and differences between the present model and super/subloading surface model are also discussed in detail.
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Isotropic hardening model for soils considering stress-induced anisotropy 査読あり
M. Kikumoto, H. Kyokawa, T. Nakai, F. Zhang, M. Hinokio
NEW FRONTIERS IN CHINESE AND JAPANESE GEOTECHNIQUES 278 - 289 2007年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：CHINA COMMUNICATIONS PRESS
A simple method for describing stress-induced anisotropy of soils, which obeys isotropic hardening rule in modified stress space, is proposed. In present study, a modified stress t(ij), by which influence of intermediate principal stress on deformation and strength characteristics of soils is suitably taken into account, is extended to a new stress tensor t(ij)(*) to be able to consider inclusively the fabric change of soils due to the variation of the intermediate principal stress and the stress histories, namely, stress-induced anisotropy. The evolution rule of t(ij)(*) is provided referring to the past experimental and numerical evidences. In this paper, the modified stress t(ij)(*) is applied to an isotropic hardening elastoplastic model named subloading t(ij) model as an example. The proposed model is verified by results of true triaxial tests.
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Extension of subloading t<inf>ij</inf> model to structured soils 査読あり
M. Kikumoto, T. Nakai, F. Zhang, M. Hinokio, A. Yagyu, H. Kyokawa
Proceedings of the International Symposium on Geomechanics and Geotechnics of Particulate Media - Geomechanics and Geotechnics of Particulate Media 305 - 311 2006年
掲載種別：研究論文（国際会議プロシーディングス）
An elastoplastic constitutive model for clay and sand is proposed, which can describe not only the typical behaviors of normally and over consolidated soils under general stress conditions, but also the behaviors of structured soils that can be found in natural deposited ground. In order to describe the behaviors of structured soils, the superloading surface concept originally proposed by Asaoka et al. (1998) is introduced. In the present model, the structured state of soil is simply defined as the difference of void ratio between the structured and the completely remolded soil under the same stress conditions. The proposed model is verified by oedometer tests on manmade structured soils. Moreover, the characteristics of the proposed model are investigated theoretically for drained and undrained triaxial tests. © 2006 Taylor & Francis Group.
