論文 - 京川 裕之
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黄鉄鉱を含む泥岩の酸化手法に関する基礎的検討 査読あり
財満 陽己，京川裕之，籾山航輝
第36回中部地盤工学シンポジウム 2024年08月
記述言語：日本語 掲載種別：研究論文（研究会，シンポジウム資料等）
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Liquefaction behaviour of aluminium and plastic rod assemblies using bi-axial apparatus with application of image analysis 査読あり 国際共著
Rawiwan Sukhumkitcharoen, Junichi Koseki, Hiroyuki Kyokawa, Masahide Otsubo
E3S Web of Conferences 544 10002 - 10002 2024年07月
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：EDP Sciences
It has recently been shown that the overall deformation characteristics of granular materials during liquefaction seems to be governed by local void ratio characteristics. The aim of this study is to investigate the relationship between mechanical properties and local void ratio changes during liquefaction in two materials of different weights (aluminium-type and plastic-type rod assemblies). A series of constant-volume cyclic bi-axial loading tests was conducted together with the image analysis obtaining local void behaviour. The experimental results demonstrate that the first liquefaction resistance of the plastic sample is higher than the aluminium one, corresponding to its smaller initial void ratio and less contractive behaviour observed in the early stage of drained monotonic compression. However, after experiencing the first liquefaction and subsequent re-consolidation histories, a liquefiable assembly of aluminium and plastic rods both became either denser (densification) or more homogenous (homogenization) in terms of local void ratio, suggesting an increase in liquefaction resistance in the next liquefaction stage. This work also includes a preliminary analogous study using a semi-3D discrete element method (DEM) with one single layer of spherical particles to simulate the similar liquefaction behaviour observed in the laboratory tests.
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地山の堆積構造に着目したトンネルの時間遅れ変状メカニズムに関する検討 査読あり 国際共著
劉長建，崔瑛，京川裕之，菊本統，池田慧生
岩盤力学に関するシンポジウム講演集 50 ( 1 ) 2024年01月
記述言語：日本語 掲載種別：研究論文（研究会，シンポジウム資料等）
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Water and soil particle movement in unsaturated bentonite with constrained and free swelling boundaries 査読あり
Hailong Wang, Yuka Yamamoto, Hiroyuki Kyokawa, Daichi Ito, Hideo Komine
Soils and Foundations 63 ( 4 ) 101350 - 101350 2023年08月
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Experimental investigation of local chemo-mechanical behaviour and temporal development of osmotic consolidation in expansive clay 査読あり
Misa Hiraga, Hiroyuki Kyokawa, Junichi Koseki
Canadian Geotechnical Journal 2023年05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：CANADIAN SCIENCE PUBLISHING
A series of one-dimensional cation infiltration tests under different drainage/infiltration conditions, infiltration times, ion concentrations (Na+), and vertical stresses were performed to comprehensively understand the osmotic consolidation of bentonite. The local behaviour of the specimen was captured on a digital camera through a transparent acrylic oedometer ring by tracking the movements of the marker sands on the side of the specimen. The Na+ concentration of the pore fluid throughout the specimen was measured after the test to investigate the spatiotemporal relationships between consolidation behaviour and cation infiltration. In the initial period of infiltration, the pore water pressure measured at the undrained bottom increased. A local swelling behaviour inside the specimen was observed during osmotic consolidation. The low permeability of expansive soils obstructs osmotically induced water drainage from the interlayer space of the expansive clay mineral, especially in regions far from the drainage boundary. This transition of pore water pressure affects the local mechanical behaviour; the dissipation of pore water pressure is followed by settlement. Therefore, the process of osmotic consolidation is totally longer than that of pure mechanical consolidation.
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Liquefaction characteristics in triaxial tests under various gravity environments – DEM analyses 査読あり
Masahide Otsubo, Sanjei Chitravel, Reiko Kuwano, Hiroyuki Kyokawa, Junichi Koseki
Computers and Geotechnics 156 105245 - 105245 2023年04月
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A new index for the strength analysis and prediction of cement-mixed soils 査読あり
Tuan A. Pham, Hiroyuki Kyokawa, Junichi Koseki, Daniel Dias
EUROPEAN JOURNAL OF ENVIRONMENTAL AND CIVIL ENGINEERING 27 ( 4 ) 1512 - 1534 2023年03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：TAYLOR & FRANCIS LTD
In geotechnical projects involving soft soils, cement-mixed soils are an excellent way to improve the mechanical behaviour and engineering performance of soils. The water-to-cement ratio, cement content, and porosity are the most critical parameters impacting the strength of cement-mixed soils, but their effects are less well understood. The proportional influence of cement amount, porosity, and moisture content on cement-mixed soil strength is investigated in this research. The results showed that as the water-to-cement ratio increases, the influence of cementation and porosity on unconfined compressive strength decreases. The blended volume ratio is proposed as a new and adequate index for evaluating cement-mixed soil strength based on the experimental results. The blended volume ratio is the product of the void/cement volume ratio and the water/cement volume ratio. While the current index has not fully addressed the important effects of the water-to-cement ratio and porosity, the blended volume ratio allows describing the concurrent influences of porosity, cement amount, and water amount on the strength development. The experimental results showed that the cement-mixed soil strength is a function of the blended volume ratio. An empirical equation based on the blended volume ratio was then proposed for predicting the strength of cement-mixed soils. The validation of the proposed equation is verified by strength analysis for several different test data sets. A good agreement between measured and predicted results indicated that the proposed model is applicable to predict well the strength of cement-mixed soils.
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背面にEPS盛土を有する橋台の動的遠心模型実験 に対する検証解析 査読あり
西剛整，鳥居剛，窪田達郎，京川裕之，古関潤一，小浪岳治
ジオシンセティックス論文集 37 2022年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
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Experimental investigation of local chemo-mechanical behaviour and temporal development of osmotic consolidation in expansive clay 査読あり
Misa Hiraga, Hiroyuki Kyokawa and Junichi Koseki
Canadian Geotechnical Journal 2022年11月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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背面にEPS盛土を有する橋台の動的遠心模型実験に対する検証解析
西 剛整, 鳥居 剛, 窪田 達郎, 京川 裕之, 古関 潤一, 小浪 岳治
ジオシンセティックス論文集 37 77 - 84 2022年10月
記述言語：日本語 出版者・発行元：国際ジオシンセティックス学会 日本支部
橋台背面にEPS盛土を用いた動的遠心模型実験の結果から，地震時にEPS盛土に用いるRCの中間床版と橋台の衝突によると考えられる大きな作用力が生じることが報告されている．本報は，この現象の確認と床版からの作用力による橋台への影響を評価するために実施した検証解析の結果を示したものである．解析はFEMにより，実験と同一スケールの三次元モデルを用いた動的解析とした．解析の結果，中間床版による橋台への作用力が発生するが，その発生時刻は橋台の背面側に慣性力が生じる時であることなど実験と同様の挙動が確認できた．また，橋台への作用の影響は土圧よりも慣性力によるものが大きいことや，中間床版からの作用力に対して床版の一部をEPS材に置換える対策の効果を確認した．
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Linking inherent anisotropy with liquefaction phenomena of granular materials by means of DEM analysis 査読あり
Masahide Otsubo, Sanjei Chitravel, Reiko Kuwano, Kevin J. Hanley, Hiroyuki Kyokawa, Junichi Koseki
Soils and Foundations 62 ( 5 ) 101202 - 101202 2022年10月
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Mechanical Behaviour and Stress-Strain Recovery Characteristics of Expanded Polypropylene 査読あり
Z. Maqsood, J. Koseki, H. Kyokawa
Geosynthetics International 2022年09月
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A new index for the strength analysis and prediction of cement-mixed soils 査読あり
Pham, A. T., Kyokawa, H., Koseki, J. and Dias, D.
European Journal of Environmental and Civil Engineering 2022年06月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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Evaluation of residual strength characteristics of reconstituted volcanic soil at Atsuma town, Hokkaido with stacked-ring shear tests 査読あり
Kenji Watanabe, Hiroyuki Kyokawa, Tomoya Onodera, Junichi Koseki and Yudai Aoyagi
Proceedings of the 20th International Conference on Soil Mechanics and Geotechnical Engineering 267 2022年05月
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）
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Shaking table tests on bridge abutments reinforced by EPS and geogrid 査読あり
H. Kyokawa, Y. Yamazaki, J. Koseki, T. Konami, T. Nishi, T. Kubota
GEOSYNTHETICS INTERNATIONAL 29 ( 2 ) 163 - 173 2022年04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：ICE PUBLISHING
This study is aimed at improving the seismic stability of bridge abutments. To study the effects of the combined use of a block of expanded polystyrene (EPS) and geogrid, a series of 1 g shaking table tests were conducted on a reduced-scale model of a cantilever-type bridge abutment and its backfill soil. The experiment results indicated that the base sliding and tilting of the wall can be further reduced by partly replacing the backfill soil with blocks of EPS, in combination with the use of the middle-height geogrid. Moreover, the relative settlement of the backfill soil at the interface with the wall could be reduced by the combined use of EPS and geogrid. Furthermore, the resultant normal force and rotational moment acting on the wall from the backfill soil during excitation also became small for the reinforced wall with both EPS and geogrid.
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Mechanism of wetting–induced deformation and failure of unsaturated soils 査読あり
Veerayut Komolvilas, Mamoru Kikumoto, Hiroyuki Kyokawa
International Journal for Numerical and Analytical Methods in Geomechanics 46 ( 6 ) 1064 - 1092 2022年02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：Wiley
The mechanisms of hydraulic collapse (wetting-induced deformation) are studied through a series of simulations using a model for unsaturated soils. The model is a critical state soil model extended for unsaturated soils using Bishop's effective stress tensor, the state boundary surface (SBS) moving with the change in the degree of saturation, and a rational soil-water characteristic curve that takes account of density and hydraulic hysteresis. Comparisons with published experimental data validate the proposed model. The simulation results show that the model adequately captures the hydraulic collapse behavior under both isotropic and anisotropic stress conditions. The effects of density, mean net stress, and deviatoric stress on the hydraulic collapse behavior are further investigated through a parametric calculation, and the mechanics of the wetting-induced instability are discussed. The effects of suction history, namely repeated wetting and drying cycles, on the deformation and failure, are also presented. The proposed model provides a validated method for modeling hydromechanical collapse in unsaturated soil and provides a better understanding of the mechanisms involved.
DOI： 10.1002/nag.3336
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A double structure model for hydro-mechano-chemical behavior of expansive soils based on the surface phenomena of mineral crystals 査読あり
Hiroyuki Kyokawa
Engineering Geology 294 106366 - 106366 2021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：Elsevier BV
It is well known that the typical swelling behavior of expansive soils is mainly caused by the nanoscale electrochemical phenomena on the surface of their main constituent mineral (i.e., smectite). In this study, the hydromechano-chemical (HMC) model for unsaturated expansive soils, which combines the macroscale soil skeleton behavior and the nanoscale interlaminar behavior of mineral crystals based on the surface phenomena is proposed within a double structure framework. The soil skeleton behavior is modeled using the Cam clay type model based on Bishop's effective stress, which considers the degree of saturation-induced hardening. Thus, it is capable of describing hydraulic collapse. Furthermore, the interlaminar behavior is demonstrated through the interlaminar force equilibrium of clay mineral crystals. To describe the swelling process during wetting, namely the crystalline and osmotic swellings, the hydration and osmotic forces acting on the mineral crystals are related to the degree of saturation. Through simulations of a series of the suction-controlled oedometer tests and the swelling pressure tests with various solutions for FEBEX bentonite, it is indicated that the proposed model demonstrates that it can comprehensively describe the typical HMC behavior of expansive soils.
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Mechanical behaviour and loading rate dependency of gypsum-mixed fine-grained soils
Masum Shaikh, Hiroyuki Kyokawa, Zain Maqsood, Md. Kamrul Ahsan, Junichi Koseki
PROCEEDINGS OF THE INSTITUTION OF CIVIL ENGINEERS-GEOTECHNICAL ENGINEERING 176 ( 2 ) 166 - 177 2021年08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：ICE PUBLISHING
Gypsum is regarded as an environmentally friendly binding material and is widely used to enhance the engineering properties of soft fine-grained soils. However, the time-dependent strength and deformation characteristics of fine-grained soils stabilised with gypsum have not yet been thoroughly investigated and rational evaluation of these characteristics will assist in the formulation of cost-effective and reliable design approaches. In this study, the time-dependent mechanical behaviours of gypsum-mixed fine-grained soil (GMFS) specimens were investigated under unconfined monotonic loading conditions, considering ageing periods of 3-90 days and five different loading rates (LR = 0.0005-1.0%/min). The results revealed that the unconfined compressive strength and stiffness of the GMFS specimens initially decreased with ageing and finally became stable after 14 days and 28 days of ageing for water/gypsum ratios of 1.30 and 1.60, respectively. Furthermore, the strength and stiffness of the GMFS specimens increased with an increase in LR.
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Experimental study on hardening characteristics and loading rate dependent mechanical behaviour of gypsum mixed sand 査読あり
Zain Maqsood, Junichi Koseki, Md Kamrul Ahsan, Masum Shaikh, Hiroyuki Kyokawa
Construction and Building Materials 262 2020年11月
掲載種別：研究論文（学術雑誌）
© 2020 Elsevier Ltd Gypsum is among the widely used construction materials, and is nowadays been considered for a variety of applications including soil stabilization, foundation works, grouting and brick manufacturing etc. Considering this prevalent utilization of gypsum in construction industry, a comprehensive study was conducted to examine the time-dependent strength and deformation characteristics of Gypsum Mixed Sand (GMS) by examining the hardening characteristics (up to nine months) and loading rate (up to five folds); under unconfined monotonic loading conditions. Effects of different factors including gypsum content, hemihydrate batches and interaction between ageing and loading rate were considered to rationally comprehend the time-dependent mechanical behaviour of GMS. The results revealed an obvious reduction in the peak strength of GMS during the initial month of ageing, and no further effects of ageing were witnessed afterwards. Moreover, a unique and significant dependency of strength and deformation on the loading rate was observed for GMS, and this behaviour was categorized into three different zones of loading rates.
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Constitutive model describing the hydro-mechanical behaviors of compacted bentonite clay based on the crystal phenomena 査読あり
Kyokawa, H.
E3S Web Conf., 2nd International Conference on Energy Geotechnics (ICEGT 2020) 205 2020年11月
担当区分：筆頭著者 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）
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Constitutive model describing the hydro-mechanical behaviors of compacted bentonite clay based on the crystal surface phenomena 査読あり
Hiroyuki Kyokawa
E3S Web Conf. (2nd International Conference on Energy Geotechnics (ICEGT 2020)) ( 205 ) 2020年11月
担当区分：筆頭著者 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）
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Experimental study on the mechanical behaviour of bounded geomaterials under creep and cyclic loading considering effects of instantaneous strain rates 査読あり
Zain Maqsood, Junichi Koseki, Yukika Miyashita, Jiren Xie, Hiroyuki Kyokawa
Engineering Geology 276 2020年10月
掲載種別：研究論文（学術雑誌）
© 2020 Elsevier B.V. Rational evaluation of the long-term performance of large-scale foundations, tunnels and natural slopes located in seismically active areas necessitates accurate assessment of the strength and deformation characteristics of bounded geomaterials, such as natural rocks and cemented soils, under creep and cyclic loading conditions. In the present study, a unique approach for examining the induced instantaneous loading/strain rates during unconfined creep and cyclic loading was adopted to unveil the effects of creep and cyclic loading on the mechanical behaviour of laboratory-produced bounded geomaterial, namely Gypsum Mixed Sand (GMS). At first, a series of unconfined monotonic tests at six different strain rates ranging from 5.3E+0 to 2.1E-5%/min were conducted on GMS. Subsequently, the mechanical behaviour of the GMS was examined under unconfined creep/sustained loading at four different stress levels. Further, these results were compared with a number of unconfined cyclic loading tests performed at different stress amplitudes. Identical patterns of the variations of axial strain accumulation and instantaneous strain rates were observed during the creep and cyclic loading. Based on the relationships between the failure stress/strain and the corresponding instantaneous strain rate, the mechanical behaviour of the GMS specimens subjected to creep and cyclic loading was found to be similar to each other, and was distinctively different than those under monotonic loading condition.
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A method for extending a general constitutive model to consider the electro‐chemo‐mechanical phenomena of mineral crystals in expansive soils 査読あり
Hiroyuki Kyokawa, Shintaro Ohno, Ichizou Kobayashi
International Journal for Numerical and Analytical Methods in Geomechanics 44 ( 6 ) 749 - 771 2020年04月
担当区分：筆頭著者 掲載種別：研究論文（学術雑誌） 出版者・発行元：Wiley
© 2020 John Wiley & Sons, Ltd. The mechanical behavior of expansive soils varies according to the chemical composition of the pore fluid. It is well known that electrochemical phenomena on the surface of clay mineral crystals considerably affect their macrostructural behavior. In particular, a change in the pore fluid composition causes osmotic consolidation or swelling. In this study, a model is constructed to describe the characteristic behavior of expansive soils by coupling the interlaminar behavior of clay mineral crystals and the soil skeleton behavior. The interlaminar behavior is derived from the electro-chemo-mechanical coupling equilibrium of mineral crystals, and the soil skeleton behavior is given by a general elastoplastic constitutive model for soils. This modeling approach extends a general model to consider the electro-chemo-mechanical phenomena of mineral crystals. Oedometer tests with the replacement of the cell fluid and the swelling pressure and deformation tests on expansive clays are simulated with the proposed model. The simulation results indicate that the proposed method can reasonably represent the typical behavior of expansive soils.
DOI： 10.1002/nag.3026
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発泡ポリプロピレンブロックの強度・変形特性に及ぼすひずみ履歴とその後のクリープ期間の影響
京川 裕之, 古関 潤一
ジオシンセティックス論文集 35 103 - 108 2020年
記述言語：日本語 出版者・発行元：国際ジオシンセティックス学会 日本支部
地震などの過去に受けた荷重履歴によってEPS盛土が潜在的なダメージを受けても，そのまま供用継続できたり，あるいは少なくとも本復旧までの期間は暫定供用できることが望ましい．そのため，EPS等軽量化材料の荷重・変状履歴に対する復元性能を把握することは重要である．本研究では，緩衝特性および復元特性に優れているとされる発泡ポリプロピレン（EPP）ブロックについて，載荷ひずみ速度，ひずみ履歴，除荷後のクリープ期間を変えた一軸圧縮試験によりその強度・変形特性の検証を行った．実験結果より，EPPブロックの応力ひずみ関係は弾粘塑性挙動を示し，除荷後の残留ひずみは時間とともに減少，つまりクリープ膨張し，同時に再載荷剛性も増加することが確認された．
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Effects of loading rate on strength and deformation characteristics of gypsum mixed sand 査読あり
Zain Maqsood, Junichi Koseki, Hiroyuki Kyokawa
E3S Web of Conferences 92 2019年06月
掲載種別：研究論文（国際会議プロシーディングス）
© The Authors, published by EDP Sciences. It has been unanimously acknowledged that the strength and deformation characteristics of bounded geomaterials, viz. cemented soils and natural rocks, are predominantly governed by the rate of loading/deformation. Rational evaluation of these time-dependent characteristics due to viscosity and ageing are vital for the reliable constitutive modelling. In order to study the effects of ageing and loading/strain rate (viscosity) on the behaviour of bounded geomaterials, a number of unconfined monotonic loading tests were performed on Gypsum Mixed Sand (GMS) specimens at a wide range of axial strain rates; ranging from 1.9E-05 to 5.3E+00 %/min (27,000 folds), and at different curing periods. The results indicate shifts in the viscous behaviour of GMS at critical strain rates of 2.0E-03 and 5.0E-01 %/min. In the light of this finding, the results are categorized into three discrete zones of strain rates, and the behaviour of GMS in each of these zones is discussed. A significant dependency of peak strength and stress-strain responses on strain rate was witnessed for specimens subjected to strain rates lesser than 2.0E-03 %/min, and the effects of viscosity/strain rate was found to be insignificant at strain rate higher than 5.0E-01%/min.
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Experimental and analytical investigations of volume change behaviour of saturated expansive soils in oedometer test 査読あり
Misa Hiraga, Hiroyuki Kyokawa, Junichi Koseki
E3S Web of Conferences 92 2019年06月
掲載種別：研究論文（国際会議プロシーディングス）
© The Authors, published by EDP Sciences. The chemical and mechanical behaviours of saturated bentonite were experimentally and analytically investigated. A series of oedometer tests on saturated bentonite was conducted. By replacing the cell fluid during the oedometer test, one-dimensional osmotic consolidation and swelling behaviour were observed. The experimental results were simulated numerically using a constitutive model by considering the influence of electrochemical phenomena of clay mineral crystals on the macrostructural behaviour. It was concluded that the typical mechanical swellability of water-saturated bentonite in oedometer test is affected by a positive dilatancy behaviour due to the lower shear strength. After the osmotic consolidation test, a lateral contraction of the specimen in the oedometer was observed; this affected the compressibility during the subsequent mechanical consolidation. It was also concluded that the concentration of Na+ in the pore fluid affects the specific mechanical properties of bentonite.
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A system to measure permeability of unsaturated soils using local pin-type sensors in triaxial apparatus 査読あり
Jaylord U.Tan Tian, Junichi Koseki, Hailong Wang, Hiroyuki Kyokawa, Takeshi Sato
7th Asia-Pacific Conference on Unsaturated Soils, AP-UNSAT 2019 7 ( 2 ) 305 - 309 2019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：The Japanese Geotechnical Society
© 2019 7th Asia-Pacific Conference on Unsaturated Soils, AP-UNSAT 2019. All rights reserved. This paper describes development of a triaxial permeameter apparatus for measuring coefficient of permeability of unsaturated soils by directly measuring the head difference between two points in a specimen using local pin-type sensors. The local pin-type sensors are made of stainless steel wrapped with membrane filter to measure suction. The apparatus includes the measurement of inflow rate by Mariotte's bottle and a weighing scale, while outflow rate is measured by burettes and a differential pressure transducer (DPT). Typical results show that the steady state flow condition can be achieved by using membrane filters to allow passage of water but prevent flow of free air. At steady state flow condition and reasonably stable measured head by the local pin-type sensors, permeability values were obtained by simple average.
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EPS盛土の実大振動台実験による新型緊結金具の効果とロッキング対策の評価 査読あり
西 剛整, 谷 美宏, 林 夏希, 窪田 達郎, 京川 裕之, 古関 潤一, 小浪 岳治
ジオシンセティックス論文集 34 ( 0 ) 153 - 160 2019年
記述言語：日本語 出版者・発行元：国際ジオシンセティックス学会 日本支部
本論文は，発泡スチロールを用いた土木工法（EDO-EPS工法）について，2011年東北地方太平洋沖地震のような継続時間の長い地震動や，2016年熊本地震に見られた震度7クラスの地震動が連続するような地震を想定して，耐震性能を強化した新型緊結金具の効果確認のための実大振動台実験を行った結果を示したものである．また，同時にトップヘビーな構造体であるEPS盛土のロッキングの影響を考慮し，これによる変状を軽減するための対策工の検討を行っている．実験の結果，従来用いられている緊結金具に比較して新型金具は変状を抑制できることが確認された．また，緊結金具の配置条件に対する工夫と，変状が生じやすい床版部において滑動を抑止するずれ止め鋼板を設けることで，ロッキングによる変状は軽減できることがわかった．
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EPSブロックとジオグリッドを併用した橋台の耐震対策に関する振動台実験 査読あり
京川 裕之, 川崎 広樹, 古関 潤一, 小浪 岳治, 西 剛整, 窪田 達郎
ジオシンセティックス論文集 34 ( 0 ) 161 - 168 2019年
記述言語：日本語 出版者・発行元：国際ジオシンセティックス学会 日本支部
本研究では，既往研究で効果が確認されているジオグリッド補強土とEPSブロックの併用に加え，ネイリングを考慮した補強土工法による橋台および背面地盤の耐震対策を模型振動台実験で検証した．実験では，ジオグリッド，EPSブロック，ネイリングを様々に組み合わせた計６ケースの橋台背面補強土に対して，正弦波を段階的に与えた．実験結果から，ジオグリッド補強土とEPSブロックを併用した場合，裏込め地盤の上段にジオグリッド，中段にEPSブロックをそれぞれ配置することで，地震時における擁壁の変位・傾斜ならびに背面地盤の沈下を抑制できることが示された．また，これらジオグリッド補強土とEPSブロックに加えて，ネイリングを設置することでその耐震性が向上することを確認した．
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Reconnaissance of the 2017 Puebla, Mexico earthquake 査読あり
Yolanda Alberto, Masahide Otsubo, Hiroyuki Kyokawa, Takashi Kiyota, Ikuo Towhata
Soils and Foundations 58 ( 5 ) 1073 - 1092 2018年10月
掲載種別：研究論文（学術雑誌）
© 2018 A normal-fault earthquake (Mw = 7.1) occurred in the state limit of Puebla and Morelos on September 19, 2017, exactly 32 years after the 1985 Michoacan Earthquake. A total of 5765 buildings suffered damage in Mexico City and about 300 in Puebla City. The authors carried out a reconnaissance of Mexico City, and some locations in the states of Puebla and Morelos, to identify the affected areas and the extent of damage. This report is a summary of the damage characteristics observed during the survey for both structural and geotechnical aspects. A series of microtremor measurements were taken to understand the ground motion characteristics in three key areas of the Mexico City Basin. The results are presented and compared to the data gathered from the accelerograph network available in Mexico, and the damage characteristics are discussed. Whenever relevant, the conditions before the earthquake are compared with the damage encountered by the inclusion of photographs. In order to understand the extent of the damage incurred by the 2017 earthquake, an overview is provided of the geological and geotechnical conditions of Mexico City, which is renowned for its soft soils and problems associated with those soils. Given that the 1985 Michoacan Earthquake established the standards for seismic design in Mexico City, this report provides background on the effects of the 1985 earthquake and comparisons are made with the Puebla earthquake.
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緊結金具を用いたEPS構造体の地震時挙動 査読あり
西 剛整, 塚本 英樹, 谷 美宏, 林 夏希, 小浪 岳治, 林 豪人, 古関 潤一, 京川 裕之, 安原 一哉, 窪田 達郎
ジオシンセティックス論文集 33 ( 0 ) 191 - 196 2018年
記述言語：日本語 出版者・発行元：国際ジオシンセティックス学会 日本支部
EDO-EPS盛土は所定の緊結金具を所要数用いることにより大規模地震においても耐震性能が確保できることが実大規模の耐震実験で確認されている．一方で近年，2011年東北地方太平洋沖地震のような継続時間の長い地震動や，2016年熊本地震のように震度7クラスの地震動が連続するなど，これまで想定されていない地震の発生が続いている．このような中で，EPS盛土の耐震性をさらに向上させ，複数回の大規模地震に対してもより高い健全性を確保することが期待されている．本論文では新しい緊結金具の現場での作業性，静的なせん断抵抗を検証した結果を示し，従来の緊結金具より効果が高いこと報告する．また緊結金具を用いたEPS盛土の小型振動台実験の結果，所定数の緊結金具を用いて，中間床版上のロッキング対策を施すことで耐震性が高まることを明らかにする．
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EPSブロックとジオグリッドを併用した擁壁の耐震対策に関する振動台実験 査読あり
京川 裕之, 山崎 佑太朗, 古関 潤一, 小浪 岳治, 西 剛整, 窪田 達郎
ジオシンセティックス論文集 33 ( 0 ) 197 - 204 2018年
記述言語：日本語 出版者・発行元：国際ジオシンセティックス学会 日本支部
本研究では，ジオグリッド補強土擁壁の高い耐震性に加えて，擁壁躯体とその裏込め土の境界部にEPSブロ ックを配することで,擁壁と背面地盤一体の耐震性を高める工法の効果を1g場での模型振動実験により検証した．実験では，無補強の片持ち梁式擁壁，条件が異なるジオグリッド補強土擁壁とEPSブロック・ジオグリッ ド併用補強擁壁をぞれぞれ2ケースに対して，正弦波を段階的に与えた．実験結果から，ジオグリッド補強士 と唾Sブロックを併用した場合，裏込め土のより上層にEPSブロックを配置することで,擁壁の変位・傾斜お よび背面地盤の沈下麓が大きく抑制された．そして， これらの補強効果は，上方にEPSブロックがあることで 擁壁に作用する地震時土圧およびモーメントが低減されたためであることが示された．
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Isogeometric analysis of THM coupled processes in ground freezing 査読あり
Yared W. Bekele, Hiroyuki Kyokawa, Arne M. Kvarving, Trond Kvamsdal, Steinar Nordal
Computers and Geotechnics 88 129 - 145 2017年08月
掲載種別：研究論文（学術雑誌）
© 2017 Elsevier Ltd An isogeometric analysis (IGA) based numerical model is presented for simulation of thermo-hydro-mechanically (THM) coupled processes in ground freezing. The momentum, mass and energy conservation equations are derived based on porous media theory. The governing equations are supplemented by a saturation curve, a hydraulic conductivity model and constitutive equations. Variational and Galerkin formulation results in a highly nonlinear system of equations, which are solved using Newton-Raphson iteration. Numerical examples on isothermal consolidation in plane strain, one-dimensional freezing and heave due to a chilled pipeline are presented. Reasonably good agreements were observed between the IGA based heave simulations and experimental results.
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Effect of slaking on direct shear behaviour of crushed mudstones 査読あり
Keshab Sharma, Takashi Kiyota, Hiroyuki Kyokawa
Soils and Foundations 57 ( 2 ) 288 - 300 2017年04月
掲載種別：研究論文（学術雑誌）
© 2017 This study investigates the effects of wetting and drying cycles, known as slaking, on the strength-displacement characteristics of crushed mudstone. A series of direct shear tests was conducted by simulating cyclic wetting and drying under different stress conditions using a modified direct shear apparatus. The effects of the stress ratio, the density of specimen, the initial water content before wetting, the slaking index, and the number of wetting and drying cycles on the test results was investigated. Experiments were also performed on less-slakable materials, including crushed sand stone, silica sand and glass beads, to compare the results with the crushed mudstone. Considerable creep displacement on the crushed mudstones was observed during both drying and wetting phases under the constant shear stress conditions. The creep displacement during the drying was more significant than during the wetting phase. The creep displacement accumulated with progressive wetting and drying cycles. The drying-induced displacement was observed when the water content became smaller than the amount of water absorption of the mudstone specimens. Correspondingly, a gradual decrease of the peak stress ratio was observed with the number of wetting and drying cycles. In contrast to the mudstones, the influence of cyclic wetting and drying on the crushed sand stone, silica sand and glass beads is almost negligible. A higher slaking index, a lower water content before wetting, and lower initial density accelerate the slaking of mudstones.
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ＴＲＵ廃棄物地層処分施設の化学的変遷を考慮した長期力学挙動解析コードの開発 査読あり
三原 守弘, 平野 史生, 高山 裕介, 京川 裕之, 大野 進太郎
原子力バックエンド研究 24 ( 1 ) 15 - 26 2017年
記述言語：日本語 出版者・発行元：一般社団法人 日本原子力学会 バックエンド部会
<p> TRU廃棄物地層処分施設の長期力学挙動を評価するための解析コードMACBECEを開発した．解析コードには，セメント系材料からのカルシウムの溶出やベントナイト系材料のカルシウム型化およびスメクタイトの溶解などの化学的変遷に伴う力学特性変化および処分施設と周辺岩盤との力学的な相互作用を考慮した．開発した解析コードを用いてクリープ変形が生じやすいと考えられる軟岩サイトを想定し，TRU廃棄物地層処分施設の建設段階から，処分施設閉鎖後10万年までの力学挙動解析を行った．緩衝材の力学挙動モデルとして，ECモデルを用いることで応力が降伏曲面の特異点付近に陥ることを解消し，数値解析上，安定な解を得ることができた．さらに，周辺岩盤と処分施設の力学的相互作用を同時に解析することにより，周辺岩盤と処分施設の力学挙動を別々に解析した第2次TRUレポートの結果と比較して処分坑道の内径変位量が半分程度となることが示された．</p>
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Ultimate Lateral Resistance of Piles in Soils Based on Active Pile Length 査読あり
Mary Roxanne Aglipay, Kazuo Konagai, Takashi Kiyota, Hiroyuki Kyokawa
Geotechnical Hazards from Large Earthquakes and Heavy Rainfalls 525 2016年09月
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Effect of in-situ sample quality on undrained cyclic strength and liquefaction assessment 査読あり
T. Kiyota, T. Ikeda, Y. Yokoyama, H. Kyokawa
Soils and Foundations 56 ( 4 ) 691 - 703 2016年08月
掲載種別：研究論文（学術雑誌）
© 2016 Japanese Geotechnical Society This study investigates the effects of quality of in-situ sandy samples, which were taken by a conventional tube sampling (TS) method, on liquefaction assessment. The sandy samples were retrieved from a loose fill layer and medium-dense Holocene deposit in young reclaimed land in Urayasu City where significant liquefaction occurred during the 2011 off the Pacific Coast of Tohoku Earthquake. First, a series of small strain measurements and undrained cyclic triaxial tests was conducted on the TS and reconstituted samples. Second, in order to investigate an applicability of the tested samples for the liquefaction assessment, an effective stress analysis was performed by use of soil parameters obtained from the examined samples. Input earthquake motions of the analysis are the 2011 off the Pacific Coast of Tohoku Earthquake and the 1987 Chiba Toho-oki Earthquake, the first and the second largest earthquakes the investigation site has experienced. The result of a sample quality assessment with the small strain shear moduli indicates that the TS sample retrieved from the Holocene deposit remains of high quality. In addition, for the reconstituted sample of the fill layer, since the small strain shear moduli of the sample are found to be nearly equal to those obtained at the field, it can be considered that the in-situ soil structure condition is reproduced in the reconstituted sample. According to an official report, the liquefaction resistance of the TS sample of the loose fill layer is RL20=0.38, which is much larger than that of medium-dense Holocene deposit (RL20=0.29) measured in this study. This is because the fill layer is so loose that the TS sample could have been strengthened due to disturbance during the sampling. On the other hand, the test result for the reconstituted sample of fill layer shows an appropriate level of liquefaction resistance (RL20=0.14). The results of the effective stress analysis using the soil parameters obtained from the TS sample of Holocene deposit and the reconstituted sample of fill layer show the most probable behaviors of the ground at the investigation site for both the 2011 off the Pacific Coast of Tohoku Earthquake and the 1987 Chiba Toho-oki Earthquake, which are consistent with the evidence reported after the earthquakes. The results indicate that the sample quality assessment by using a small strain shear moduli is applicable for the rational liquefaction assessment, and it would be possible to employ the reconstituted sample, which the small strain shear moduli are the same with the in-situ value, in substitution for a high quality sample.
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破砕泥岩のスレーキング現象と変形挙動 査読あり
菊本 統, 福田 拓海, 京川 裕之
土木学会論文集C（地圏工学） 72 ( 2 ) 126 - 135 2016年
記述言語：日本語 出版者・発行元：公益社団法人 土木学会
乾湿繰り返しに伴う風化現象であるスレーキングを，従来型の促進スレーキング試験と一次元圧縮条件下で湿乾履歴を与える圧縮スレーキング試験により検討した．促進スレーキング試験では，試料によるスレーキング特性の違いや，細粒化に伴う土の力学特性の不可逆な変化について考察した．圧縮スレーキング試験では，圧縮過程での粒子破砕が圧縮性の増加に寄与すること，拘束応力下のスレーキングは土の大圧縮を引き起こすことを示した．最後に，湿乾履歴を考慮した粒度指標<i>I<sub>G</sub></i>の発展則により記述し，粒度指標<i>I<sub>G</sub></i>と最大・最小間隙比や限界間隙比を関係付けることでスレーキング現象を構成則の範疇で考慮できるとの考えを示した．
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航空レーザ測量に基づく浦安市の液状化による道路沈下分析 査読あり
須山 翔太, 清田 隆, 小長井 一男, 京川 裕之, 上村 健太, 濱中 亮
土木学会論文集C（地圏工学） 72 ( 1 ) 38 - 47 2016年
記述言語：日本語 出版者・発行元：公益社団法人 土木学会
2011年東北地方太平洋沖地震により，関東地方では東京湾沿岸部に代表される若年埋立地盤を中心に顕著な液状化が発生し，それに伴う構造物の様々な被害が発生した．本稿では，特に甚大な液状化被害が生じた千葉県浦安市を対象に，著者らが整備した液状化地盤沈下マップを用いて，液状化に起因する道路等の沈下量を抽出した．これらのデータ分析により，道路の舗装・路盤層厚が厚いほど液状化による沈下量は小さくなる傾向が確認された．また，液状化の程度を示すPL値と道路沈下量の関係においても上記の影響が認められ，液状化による地盤沈下予測やPL値に基づくハザードマップの高度化に資する結果を得た．更に，液状化対策として地盤改良が施されていた地区を対象とした沈下分析も行い，液状化後の沈下量に及ぼす地盤改良工法の効果を定量的に示した．
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TRU廃棄物処分システムの性能評価の観点からの人工バリアの透水性に対するセメント系材料のひび割れの影響に関する検討 査読あり
平野 史生, 大谷 芳輝, 京川 裕之, 三原 守弘, 清水 浩之, 本田 明
日本原子力学会和文論文誌 15 ( 2 ) 97 - 114 2016年
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：一般社団法人 日本原子力学会
The mechanical analysis code MACBECE2014 has been developed at the Japan Atomic Energy Agency (JAEA) to make realistic simulations of the physical integrity of the near field for performance assessment of the geological disposal of TRU waste in Japan. The MACBECE2014 code can be used to evaluate long-term changes in the mechanical behavior of the near field and any subsequent changes in the permeability of engineering barrier components, including crack formation in cementitious materials caused by expansion due to metal corrosion. Cracks in cementitious materials are likely to channel the flow of groundwater and so the represent preferred flow paths of any released radionuclides. Mechanical analysis was conducted using the MACBECE2014 code to investigate the concept of the TRU waste disposal system described in JAEA's Second Progress TRU Report. Simulated results of a disposal system with a bentonite buffer demonstrated that the low permeability of the engineering barrier system could be maintained for long time periods because the physical integrity of the bentonite buffer remained intact even if cracks in the cementitious components had formed locally. Simulated results of the disposal system with a concrete backfill instead of a bentonite buffer showed that crack formation leads to a significant increase in the permeability of the engineering barrier system.
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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.
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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.
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