論文 - 京川 裕之
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Effect of lattice-frame reinforced geosynthetics on seismic stability improvement of embankment on loose sand deposit 査読あり
M. Okamoto, T. Obara, Y. Nakajima, T. Yoshida, Y. Kitamoto, H. Kyokawa, Y. Sawada, K. Fujisaki
15th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering, ARC 2015: New Innovations and Sustainability 2324 - 2329 2015年
掲載種別：研究論文（国際会議プロシーディングス）
The authors have developed a specific geosynthetic for reduction of differential settlement, composed of woven textile sheet and lattice frame of mortar injected fabric hoses, providing high bending rigidity. To examine the reinforcement effect of this geosynthetic system, called the lattice-frame reinforced (LFR) sheet, a series of dynamic centrifugal model tests and finite element analyses were carried out. The results showed that the LFR sheet was capable of reducing differential settlement due to seismic liquefaction and effective to reduce horizontal deformation of liquefiable layer as well as the case in which the improved zone was totally set under the embankment.
DOI： 10.3208/jgssp.IGS-28
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Why do constitutive models using (p and q) have problems? 査読あり
T. Nakai, H. M. Shahin, M. Hinokio, H. Kyokawa
Geomechanics from Micro to Macro - Proceedings of the TC105 ISSMGE International Symposium on Geomechanics from Micro to Macro, IS-Cambridge 2014 2 683 - 688 2015年
掲載種別：研究論文（国際会議プロシーディングス）
Most constitutive models have been formulated using the stress invariants (p and q) since the Cam clay model was developed. It is known that such models cannot describe uniquely the deformation and strength of soils under three different principal stresses. Then, the concept of tij has been proposed to describe uniquely the stress-strain behaviors in general three-dimensional (3D) stress conditions. In this paper, some inevitable problems of the ordinary models are firstly clarified. After then, the meaning of the tij concept and the method to apply tij concept to elastoplastic models are presented, since the details of the tij concept were described in the previous papers. This concept was found out from the idea that the frictional law essentially governs soil behavior. Using this concept, any kinds of one-dimensional models and/or three-dimensional models formulated by using (p and q) can be easily extended to general three-dimensional models. © 2015 Taylor & Francis Group.
DOI： 10.1201/b17395-122
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Simple modeling of time-dependent behavior for structured soils 査読あり
Teruo Nakai, Hossain Md Shahin, Hiroyuki Kyokawa
Springer Series in Geomechanics and Geoengineering none 331 - 337 2015年
掲載種別：研究論文（国際会議プロシーディングス）
© Springer International Publishing Switzerland 2015. A simple model to describe time-dependent behavior of various soils in 1D stress conditions is presented in this paper. The model is formulated not using the usual viscoplastic theories such as over-stress type and non-stationary flow surface type but utilizing the subloading surface concept by Hashiguchi (1980), and paying attention to the experimental results that the normally consolidation line (NCL) on the e-ln σ plane shift depending on the strain rate. The present model can describe various time-dependent behaviors not only of normally consolidated soil but also of over consolidated and naturally deposited soils in the same manner without violating the objectivities. The 1D model can easily be extended to the 3D using the tij concept (Nakai and Mihara 1984).
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Simple modeling of time-dependent behavior for normally consolidated soil and structured soils 査読あり
T. Nakai, H. M. Shahin, H. Kyokawa
49th US Rock Mechanics / Geomechanics Symposium 2015 2 878 - 885 2015年
掲載種別：研究論文（国際会議プロシーディングス）
Copyright 2015 ARMA, American Rock Mechanics Association. Simple models to describe time-dependent behavior of geomaterials in ID and 3D stress conditions are presented. After explaining previous viscoplastic models and the problems these models contain, a new time-dependent model is presented which is formulated not using usual viscoplastic theories but utilizing the subloading surface concept by Hashiguchi [1]. Based on experimental results, it has been shown that the normal consolidation line (NCL) and the critical state line (CSL) on the e - Inσ plane can shift vertically depending on the strain rate. The model can describe time-dependent behaviors of both normally consolidated unstructured as well as structured soils in the same manner. To describe the behavior of structured soil, a state variable, ρ, which represents the influence of density, and another state variable, ω, which represents the bonding effect, are introduced. After the formulation is explained in one-dimension to highlight the fundamental concepts of the model, it is extended to three-dimensions using the tij concept [2].
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Simple Expression of the Ultimate Lateral Resistance of Piles on Sand based on Active Pile Length 査読あり
AGLIPAY Mary Roxanne, KONAGAI Kazuo, KIYOTA Takashi, KYOKAWA Hiroyuki
土木学会論文集A1（構造・地震工学） 71 ( 4 ) I_329 - I_336 2015年
記述言語：日本語 出版者・発行元：公益社団法人 土木学会
Simulation of the in-situ behavior of pile foundation is necessary in the seismic design and assessment for target structural integrity and performance during earthquakes. Generally, the pile behavior is governed by its deformation. For commonly used flexible piles, this deformation is observed to be significantly greater near the ground surface and becomes negligible with increasing depth. This region of significant deformation is defined as the active pile length, <i>L<sub>a</sub></i>. To simply investigate the behavior response of pile embedded in a homogeneous sandy soil, a plane strain condition using the 2D finite element method in nonlinear analysis was done. The subloading <i>t<sub>ij</sub></i> model is used to model the elasto-plastic behavior of the soil and the pile is modeled as a 2D continuum-based beam element. Based on the rigorous solution, piles reach the ultimate state of its side soil under large lateral deformations. In this case, a soil wedge can be observed being pushed up along this active pile length. Therefore, a simplified method using the active pile length as a key parameter to describe the ultimate lateral resistance of piles embedded in sand is presented for more practical approach in the seismic design and assessment of piles.
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Numerical simulation of thermo-hydro-mechanically coupled processes during ground freezing and thawing 査読あり
H. Kyokawa, Y. W. Bekele
Computer Methods and Recent Advances in Geomechanics - Proceedings of the 14th Int. Conference of International Association for Computer Methods and Recent Advances in Geomechanics, IACMAG 2014 379 - 384 2015年
掲載種別：研究論文（国際会議プロシーディングス）
Fully coupled Thermo-Hydro-Mechanical (THM) processes in the freezing and thawing phenomena of ground are studied numerically. Theoretical formulations for modeling the THM process of frozen soil are presented in this study. Fully saturated frozen soil composed of soil, water and ice is modeled as a homogeneous three-phase mixture (theory of multiphase mixture) and the governing equations of frozen ground are accordingly derived by combining the individual governing equations constituting phases with consideration of interaction between phases, especially water and ice phases. Those governing equations are solved by the finite element method with simple supplementary equations representing mechanical/hydraulic/thermal characteristics of frozen soil. From a parametric study on freezing process of one-dimensional soil column test, it is shown that the freezing volume change is affected by the hydraulic condition since the freezing consolidation occurs due to the changing of water pressure and effective stress at unfrozen area. © 2015 Taylor & Francis Group, London.
DOI： 10.1201/b17435-63
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On thermo-hydro-mechanically (THM) coupled finite element modeling of ground freezing and thawing 査読あり
Y. W. Bekele, H. Kyokawa
Numerical Methods in Geotechnical Engineering - Proceedings of the 8th European Conference on Numerical Methods in Geotechnical Engineering, NUMGE 2014 2 959 - 964 2014年
掲載種別：研究論文（国際会議プロシーディングス）
Fully coupled thermo-hydro-mechanical (THM) processes in the freezing and thawing phenomena of ground are studied numerically. Theoretical and numerical formulations for modeling the THM process is proposed. Porous media theory is used for deriving the governing equations in the theoretical formulation. A saturated frozen soil is assumed and this three-phase porous medium is modeled as a homogeneous continuum. The main governing equations derived in the theoretical formulation are the linear momentum balance equation, the energy balance equation and the mass balance equation for the pores. Supplementary equations in the theoretical formulation include thermodynamic equilibrium for pore pressures, a soil-water characteristic curve for the degree of water saturation, Darcy's law for water flow and Fourier's law for thermal conduction. The finite element method is used for the spatial discretization of the governing partial differential equations and the finite difference method for temporal discretization. The matrix equations are derived to accomodate both linear and nonlinear material behaviors for the constitutive equations of the soil skeleton. © 2014 Taylor & Francis Group, London.
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Rational expression of time-dependent behavior from normally consolidated soil to naturally deposited soil 査読あり
T. Nakai, H. M. Shahin, H. Kyokawa
18th International Conference on Soil Mechanics and Geotechnical Engineering: Challenges and Innovations in Geotechnics, ICSMGE 2013 1 255 - 258 2013年
掲載種別：研究論文（国際会議プロシーディングス）
Fundamental concepts of the ordinary elasto-viscoplastic modelings, which are the non-statonary flow surface model and the over-stress type model, are explained in one-dimensional (1D) compression of normally consolidated soil for easy understading. Then, a new approach to describe various time-dependent behaviors of soils is presented extending the advanced elastoplasitic theory based on the subloading surface concept without employing usual elasto-viscoplastic theories. Throughout the simulations of various time-dependent behaviors of normally consolidated clay, the features of these three types of time-denpendent models are clarified. In addtoin, 1D anlyses using the proposed model are carried out not only for normally consolidated clay but also for over-consolidated clay and strauctured clay such as nuturally deposited clay. The analytical results simulate well the features of time-dependent behavior of various clays including the delayed settlement of sturctured clay.
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Significance of t<inf>ij</inf> concept in constitutive modeling of geomatrials 査読あり
T. Nakai, H. M. Shahin, M. Hinokio, H. Kyokawa
Computational Geomechanics, COMGEO III - Proceedings of the 3nd International Symposium on Computational Geomechanics 108 - 122 2013年
掲載種別：研究論文（国際会議プロシーディングス）
© 2013 Computational Geomechanics, COMGEO III - Proceedings of the 3nd International Symposium on Computational Geomechanics. All rights reserved. Simple and unified method to describe stress-strain behavior in general three-dimensional stress condition, which has been called the tij concept, was presented by Nakai & Mihara (1984). Since this concept is based on the idea that the frictional law essentially governs soil behavior, its meaning is very clear. Using this concept, any kind of one-dimensional model and/or three-dimensional model formulated by using (p and q) can be easily extended to general three-dimensional conditions. Method for formulating the constitutive model using the tij concept and the meaning of the tij operator are reviewed. The validity of this concept is also checked by simulation of various types of shear tests in general three-dimensional conditions.
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浦安市埋立地盤の液状化被害とSWS試験結果 査読あり
横山 悠, 京川 裕之, 近藤 康人, 清田 隆
生産研究 64 ( 6 ) 853 - 857 2012年
記述言語：日本語 出版者・発行元：東京大学生産技術研究所
東北地方太平洋沖地震によって臨海部の埋立地全域で液状化が発生した千葉県浦安市の中でも，周辺隣接地域と比べて被害が大きく，被害のコントラストが明瞭な地域があった．著者らは，このような地域において，地震発生直後から定期的にスウェーデン式サウンディング試験を行い，地盤強度の変化を計測してきた．貫入抵抗の変化より，液状化は埋立砂質土層を中心に発生しており，液状化後に著しく低下した貫入抵抗は１～２カ月後には回復しているものの，依然として低い値を示している．また本稿では，貫入抵抗および地盤特性から簡易液状化判定を行い，同地域の再液状化の可能性についても検討した．［本要旨はPDFには含まれない］
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東北地方太平洋沖地震による浦安市埋立地盤の液状化被害調査 査読あり
京川 裕之, 清田 隆, 近藤 康人, 小長井 一男
地盤工学ジャーナル 7 ( 1 ) 265 - 273 2012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
東北地方太平洋沖地震によって埋立地の大部分が液状化した千葉県浦安市において，著者らは地震発生直後から航空レーザ測量，粒度分析，SWS試験などを行い，液状化による地盤の変動を継続的にかつ定量的に把握してきた。これらの調査より，(1) 浦安市の埋立地では地盤沈下が広範囲に生じており，その沈下量の分布は家屋・ライフラインの被害と対応している。(2) 同時期の埋立地（未改良地区）で，被害程度が大きく異なる場所がある。(3) 広範囲に採取した噴砂の粒度およびSPT試料の粒度は，大量の噴砂と再液状化が確認されているニュージーランド・クライストチャーチのケースと非常に似通っている。(4) 液状化により地盤の貫入抵抗は大きく低下し，その後2ヶ月程度で強度は回復・安定するが依然として低い値を示している。本稿では以上の知見より，同地区の再液状化の可能性についても検討する。
DOI： 10.3208/jgs.7.265
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ROAD BRIDGES IN MINAMI-SANRIKU WASHED AWAY IN THE MARCH 11<sup>th</sup> 2011 GREAT EAST JAPAN EARTHQUAKE AND TSUNAMI 査読あり
AGLIPAY Mary Roxanne I., KONAGAI Kazuo, KYOKAWA Hiroyuki, KESHAB Sharma
土木学会論文集A1（構造・地震工学） 68 ( 4 ) I_1307 - I_1314 2012年
記述言語：英語 出版者・発行元：公益社団法人 土木学会
On March 11<sup>th</sup>, 2011, Minami-Sanriku, located in the northeastern coast of Japan was severely inundated by the tsunami that followed the Great East Japan Earthquake on March 11, 2011. Road bridges near the coastlines in this area have been extensively damaged with their decks being overturned or carried over long distances. An attempt was made to deduce as rational scenarios as possible before remaining debris was cleaned up. Though the reasons for the washout of bridges can be many and complex, it is to be noted that bridge decks have hollows for the optimum light-weight solution, which fact eventually allowed the bridge decks to be carried over remarkable distances. Poor connection details and cavities, hollows between deck beams, are considered to have facilitated overturning due to uplift forces.
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下負荷面の考え方を利用した土の時間効果特性の表現 査読あり
中井 照夫, シャヒン ホサイン, 菊本 統, 京川 裕之
理論応用力学講演会 講演論文集 61 ( 0 ) 108 - 108 2012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」
時間効果特性を考えない弾塑性モデルを簡便に時間効果特性考えたモデルに拡張する方法について解説する。時間効果特性を考えた多くの構成モデルは例えば正規圧密に限るとか過圧密に限るなど、対象とする地盤材料を限定してモデル化され、多くは、Over stress 理論か流動曲面理論を使って定式化がなされている。さらにはこれらのモデルは時間効果特性と考えない弾塑性モデルとは別物としている。また、モデルによっては実時間が変数として構成モデルの中に入るため、客観性がないことも指摘されている。 ここでは、当研究室で取り組んできた地盤材料の諸特性を簡単且つ精緻に表現するモデル化法の一つの応用として、１次元および３次元弾塑性モデルを既往の粘塑性論を使うことなく橋口による下負荷面の考え方を利用して時間効果特性を考慮できるモデルに拡張する。そして、そのパフォーマンスを正規圧密粘土、過圧密粘土、自然体積粘土の１次元および３次元挙動の解析を通して検証する。
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SURFACE RUPTURE OF THE NORMAL SEISMIC FAULTS AND SLOPE FAILURES APPEARED IN APRIL 11<sup>th</sup>, 2011 FUKUSHIMA-PREFECTURE HAMADOORI EARTHQUAKE 査読あり
KAZMI Zaheer Abbas, KONAGAI Kazuo, KYOKAWA Hiroyuki, TETIK Cigdem
土木学会論文集A1（構造・地震工学） 68 ( 4 ) I_1285 - I_1292 2012年
記述言語：英語 出版者・発行元：公益社団法人 土木学会
On April 11<sup>th</sup>, 2011, Iwaki region of Fukushima prefecture was jolted by Fukushima-Prefecture Hamadoori Earthquake. Surface ruptures were observed along causative Idosawa and Yunotake normal faults. In addition to numerous small slope failures, a coherent landslide and building structures of Tabito Junior High School, bisected by Idosawa Fault, were found along the causative faults. A precise digital elevation model of the coherent landslide was obtained through the ground and air-born LiDAR surveys. The measurements of perimeters of the gymnasium building and the swimming pool of Tabito Junior High School have shown that ground undergoes a slow and steady/continual deformation.
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A simple and unified one-dimensional model to describe various characteristics of soils 査読あり
Teruo Nakai, Hossain M.D. Shahin, Mamoru Kikumoto, Hiroyuki Kyokawa, Feng Zhang, Marcio M. Farias
Soils and Foundations 51 ( 6 ) 1129 - 1148 2011年12月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：The Japanese Geotechnical Society
A simple and unified constitutive model for soils, considering various effects such as the influences of density, bonding, time dependent behavior and others, is presented in this paper. The elastoplastic behavior of over consolidated non-structured soils under a one-dimensional stress condition is firstly presented by introducing a state variable that represents the influence of density (stage I). To describe the one-dimensional stress-strain behavior of structured soils, attention is focused on density and bonding as the main factors that affect the response of this type of soil, because it can be considered that soil a skeleton structure which is in a looser state than that of a normally consolidated soil is formed by bonding effects (stage II). Furthermore, a simple method is presented which allows for other soil characteristics to be considered, such as time and temperature dependency, and the effect of suction in unsaturated soils. Experimental observations show that the normally consolidated line (NCL) in the void ratio-stress relation (e.g., e-ln s curve) shifts depending on the change of strain rate, temperature, suction and others (stage III). The validation of the model at stages I and II is demonstrated by simulating one-dimensional consolidation tests for normally consolidated, over consolidated and natural clays. The applicability of the model at stage III is verified not only by the simulations of time-dependent behavior of clays in one-dimensional element tests but also by the soil-water coupled finite element analysis of oedometer tests as a boundary value problem. The extension from one-dimensional models to three-dimensional models is easily achieved by defining the yield function using stress invariants instead of one-dimensional stress 'σ' and by assuming an appropriate flow rule in stress space. The details of the modeling in general three-dimensional stress conditions will be described in another paper (Nakai et al., 2011).
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A simple and unified three-dimensional model to describe various characteristics of soils 査読あり
Teruo Nakai, Hossain M.D. Shahin, Mamoru Kikumoto, Hiroyuki Kyokawa, Feng Zhang, Marcio M. Farias
Soils and Foundations 51 ( 6 ) 1149 - 1168 2011年12月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：The Japanese Geotechnical Society
A simple and unified model to describe some features of soil behavior in one dimensional condition is presented in another related paper (Nakai et al., 2011). In the present paper, this one-dimensional model is extended to describe not only the soil features explained in the related paper three-dimensionally (3D), but also to explain other soil features found in multi-dimensional conditions, such as shear behavior considering the influence of intermediate principal stress on the deformation and strength of soils, and the positive and negative soil dilatancy. Firstly, the first step in extending any kind of one-dimensional model to a three-dimensional one is explained in detail: the significance of tij concept and its stress invariants (tN and tS) is explained and compared with the idea of ordinary stress invariants (p and q) used in the Cam clay model. Then, the advanced elastoplastic relations (stages I to III) in the one-dimensional condition presented in the related paper are re-formulated as three-dimensional models-e.g., a model for over consolidated soil, a model for structured soil and a model which considers time-dependent behavior. The three-dimensional models for over consolidated soil (stage I) and structured soil (stage II) are formulated so as to coincide with the subloading tij model developed by Nakai and Hinokio (2004) and by Nakai (2007), respectively. The validity of the models in stage I and stage II is checked by simulations of various shear tests for sands with different void ratios and for over consolidated and natural clays under drained and undrained conditions. The model in stage III is verified by simulations of shear tests with different strain rates, and by simulating creep tests and others, not only for normally consolidated clay but also for non-structured and structured over consolidated clays under drained and undrained conditions.
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土の温度依存特性を考慮した弾塑性構成モデル 査読あり
菊本 統, 京川 裕之, 中井 照夫, シャヒン ホサイン, 伴 旭将
理論応用力学講演会 講演論文集 60 ( 0 ) 41 - 41 2011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」
近年，放射性廃棄物処分や熱エネルギー貯蔵，海底地下資源の開発，高電圧ケーブル埋設など様々な目的で積極的に地盤利用および開発が行われている。これに関連してしばしば課題となるのは，温度変化の影響を考慮した地盤の変形と破壊の予測である。高温条件下あるいは温度変化を伴う環境下における地盤工学上の諸問題は応力ひずみ特性・熱伝導・間隙水の流れが相互に関連した力学現象であるため，熱－水－応力の連成を考慮した数値解析も幾つか試みられているが，計算に用いられている構成モデルが地盤材料の要素レベルでの温度依存特性を適切に考慮しているとはいい難い。本研究では，過去の実験事実をレビューしながら温度変化が飽和土の応力ひずみ特性に及ぼす影響について考察を行い，それに基づいて温度変化の影響を簡潔に考慮した飽和土の構成モデルを提案する。本稿では主に一次元モデルについて説明を行うが，降伏関数を拡張して関連流れ則を仮定するだけで多次元モデルにも容易に拡張できる。
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土の飽和・不飽和特性を考慮した弾塑性構成モデル 査読あり
京川 裕之, 菊本 統, 中井 照夫, 立松 和憲, 小池 真奈, 塚本 晃平
理論応用力学講演会 講演論文集 60 ( 0 ) 48 - 48 2011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」
実地盤のほとんどは間隙が水と空気によって満たされている不飽和状態にあり，その力学特性は粒子間に残存するメニスカス水による表面張力の影響を受ける。たとえば，表面張力の影響を受けて高い剛性を示す（緩い間隙を保持する）不飽和土が，一度浸水作用を受けると表面張力を失い大きな変形（コラプス）を生じることは広く知られている。このように不飽和土の力学特性は飽和土のそれとは大きく異なるが，自然乾燥，降雨浸潤などによって飽和から不飽和および乾燥状態が刻々と変化する土の力学特性は，内部水分量の変化に対して連続的かつ統一的（飽和土構成モデルの理論がそのまま適用可能）に扱われる必要がある。そこで本研究では，保水特性と密接に関係する飽和・不飽和土の力学挙動の統一的なモデル化に加えて，乾燥・湿潤履歴および密度の影響を考慮した地盤材料の保水特性をモデル化する。提案モデルは，本研究グループが行った不飽和カオリンクレーの圧縮・せん断試験，ならびに浸水試験の結果からその広範な適用性が示される。
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東日本大震災による宮城県内の宅地造成地被災事例 査読あり
清田 隆, 京川 裕之
生産研究 63 ( 6 ) 709 - 715 2011年
記述言語：日本語 出版者・発行元：東京大学生産技術研究所
2011年3月11日に発生した東北地方太平洋沖地震（Mw 9.0）による東日本大震災では，宅地造成地において地震動による地盤の変状が多数発生し，人命・家屋に損害を与えた．いずれの造成地でも谷埋め盛土が行われた箇所に被害が集中する傾向にあった．ここでは，比較的被害の大きかった宮城県内の造成地の被害事例を報告する．また，1978年宮城県沖地震後に施工された対策工の効果についても言及する．［本要旨はPDFには含まれない］
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A simple elasto-plastic model for unsaturated soils and interpretations of collapse and compaction behaviours 査読あり
M. Kikumoto, H. Kyokawa, T. Nakai, H. M. Shahin
Unsaturated Soils - Proceedings of the 5th International Conference on Unsaturated Soils 2 849 - 855 2011年
掲載種別：研究論文（国際会議プロシーディングス）
Stress-strain behaviour of unsaturated soils seems rather different from that of saturated ones. It should however be described properly because soil may lie under an unsaturated state in the actual field. In the present study, a model taking account of the necessary characteristics of unsaturated soils is proposed by extending an existing model for saturated ones based on the Bishop's effective stress. In the model, variation in the degree of saturation is estimated by a newly proposed model for water retention curve considering the effects of hydraulic hysteresis and density, and the increase in the degree of saturation is linked with downward movement of normally consolidation line in the mean effective stress vs. void ratio plane in order to describe the typical behaviours of unsaturated soils. In the present paper, mechanisms of consolidation, soaking and compaction behaviours of unsaturated soils are discussed through the simulations by the proposed model. © 2011 Taylor & Francis Group, London.
