研究者詳細 - 中井　健太郎

論文 - 中井　健太郎

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軟弱地盤上に設置した仮設構造物の地震時安定性評価と転倒防止対策の一検討査読有り

中井健太郎，野田利弘

地盤工学ジャーナル 5 巻 ( 3 ) 頁： 499-510 2010年9月

担当区分：筆頭著者記述言語：日本語掲載種別：研究論文（学術雑誌）

比較的簡単に設置・撤去ができる仮設構造物は，設置期間が短いものの，杭の設置や地盤改良など特段の対策が施されないため，施工・設置中に地震が発生した場合，転倒による人身被害等が懸念される。本論文では，2種類の軟弱地盤（砂質地盤および粘性土地盤）上に建設された仮設構造物の地震時安定性を数値解析的に検討した。その結果，仮設構造物転倒の主たる原因は，単に加速度の増幅（最大加速度）ではなく，①仮設構造物の固有振動数と地盤の卓越振動数の一致に伴う揺れの増幅と，②表層地盤の液状化による支持力低下とそれに伴う構造物の不同沈下にあることがわかった。転倒防止対策としては，仮設構造物の幅と高さを変えることによって，構造物の固有振動数と地盤の卓越周波数を一致させないことも重要であるが，仮設構造物直下に敷設板を用いて構造物と地盤との設置面積を大きくすることが，簡単で効果的な対策となることがわかった.

Seismic response analysis of a coastal artificial reclaimed ground containing a soft layer 査読有り

Noda, T., Nakai, K. and Asaoka, A.

IOP Conference Series: Materials Science and Engineering 10 巻頁： CD, No.012107. 2010年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

The seismic resistance of a coastal artificial ground situated within the Port of Nagoya against the Tokai-Tonankai-Nankai triple-segment earthquake was assessed. The analysis was carried out using the elasto-plastic constitutive equation for soils (SYS-Cam clay model) mounted on the soil-water coupled finite element deformation analysis program The model focuses attention on the action of the soil skeleton structure, and the analysis allows description of the mechanical behavior of a wide range of soils without distinguishing between static and dynamic behavior. When considering earthquake damage, attention usually tends to focus only on the phenomenon of liquefaction in sandy grounds. In this paper, finite element analysis was employed to simulate the phenomenon of liquefaction of soft sand and, in addition, to show that because of disturbance of the soil during the earthquake, there is a danger of large settlement occurring over a long period after the earthquake in the soft clay layer directly beneath the area that is under the action of vertical loads.

部分的に固化改良したゆるい砂地盤の地震時／地震後応答解析査読有り

竹内秀克, 中井健太郎, 野田利弘

応用力学論文集 13 巻 2010年6月

Different failure modes of a clay foundation-embankment system corresponding to different incident seismic waves 査読有り

Nakai, K., Noda, T. and Asaoka, A.

ASCE Geotechnical Special Publication No.201, Soil Dynamics and Earthquake Engineering 頁： 125-130 2010年6月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

In recent years, damage to embankments from earthquakes has been frequently reported. In this paper, the deformation and failure behavior of an embankment constructed on a weak clay foundation during and after an earthquake is investigated using numerical analysis, GEOASIA, assuming a 40 g centrifugal field. The main conclusions obtained were as follows. 1) Although the embankment remained stable without large deformation during the earthquake, a slip plane subsequently penetrated through the embankment, resulting in delayed failure (circular arc slip). 2) The deformation behavior (failure mode) of the foundation and embankment varies greatly depending on the characteristics of the incident seismic motions.

Modeling and seismic response analysis of a reclaimed artificial ground 査読有り

Noda, T., Asaoka, A. and Nakai, K.

ASCE Geotechnical Special Publication No.201, Soil Dynamics and Earthquake Engineering 頁： 294-299 2010年6月

記述言語：英語掲載種別：研究論文（学術雑誌）

Compared with natural grounds formed by sedimentation over many years, reclaimed artificial grounds are often weak. In this work, modeling of a reclaimed offshore artificial ground and its seismic response analysis were carried out, and the vulnerability of the weak reclaimed layers to seismic activity is pointed out. This study was carried out using a soil-water coupled finite deformation analysis program GEOASIA incorporating an elasto-plastic constitutive model (the SYS Cam-clay model). This model is capable of describing, within a single framework, the behaviors of sands, clays, and intermediate soils consisting of sand/clay mixtures through their soil skeleton structures (structure, overconsolidation, anisotropy) and its works. In reclaimed sand, lateral flow and upward lifting of lightweight underground structures occur because of liquefaction during an earthquake. In reclaimed clay, long-term settlement, which continues for several years after the earthquake, occurs.

Seismic stability assessment of a lightweight structure on sandy/clayey foundations 査読有り

Nakai, K. and Noda, T.

Proceedings of the Fourth Japan-China Geotechnical Symposium 頁： 564-571 2010年4月

担当区分：筆頭著者記述言語：英語

For a temporary structure, which is comparatively easy to placement and withdrawal, special countermeasures such as pile penetration or ground improvement are not taken into considerations. As a consequence, when an earthquake occurs during the placement/construction, personal injury might be caused by overturning of the temporary structure. In this paper, co- and post-seismic responses of interactive systems consisting of a temporary structure - alternately layered sandy/clayey foundations were numerically investigated by using a soil-water coupled elasto-plastic finite deformation analysis. The findings are mainly as follows. 1) An unstable structure such as temporary structure become at high risk of overturning by means of liquefaction of sand layer. 2) Although it is possible to consider countermeasure against overturning by widen the breadth and lower the height of the temporary structure, it turned out that installation of a construction board is very effective.

*Structure upgradation concept applied to cyclic mobility of sand and high ductility of natural clay 査読有り

Nakai, K., Noda, T., Nakano, M. Asaoka, A. and Kawai, T.

Proceedings of 17th International Conference on Soil Mechanics and Geotechnical Engineering 頁： 175-178 2009年10月

担当区分：筆頭著者記述言語：英語

Naturally deposited sands/clays are mostly found in structured states. In addition, these are usually in overconsolidated states. Furthermore, they exhibit more or less a condition of anisotropy. In order to describe the mechanical behavior of these natural soils, the authors proposed an elasto-plastic constitutive model, namely Super/subloading yield surface Cam-clay model (E.g. Asaoka et al., 2002), in which three mechanical concepts and their evolution rules were introduced into the Cam-clay model; the first one describes `degradation of soil structure' due to ongoing plastic deformation, the second, `loss of overconsolidation', and the third, `development/loss of anisotropy'. It can be emphasized in the model that, for sand, the degradation of structure proceeds more rapidly than the loss of overconsolidation, while for clay, the loss of overconsolidation proceeds more rapidly than the degradation of soil structure. Thus, the model can describe sand and clay consistently within the same theoretical framework.
For evolution rule of soil structure, most simple one is to consider only the degradation process. But through the exhaustive observation of repeated undrained shear behavior of sand, especially pre and post cyclic mobility behavior, upgradation process of the soil structure can be truly found. So, in the present paper, the process of re-upgradeation for the soil structure due to the plastic volume expansion, i.e. the (positive) dilation, is newly introduced to the model, dividing the contribution of plastic deformation to the change of soil structure into the volumetric and deviatoric part as a sophisticated evolution rule for the soil skeleton structure. And, the importance of upgradation concept of soil skeleton structure can be showned in shear behavior of both sand and clay demonstrating their model responses
1) Sand: Cyclic mobility behavior can be described. Fig.1 shows the calculated result of repeated undrained shear behavior of medium dens

*Co-seismic and post-seismic behavior of an alternately layered sand-clay ground and embankment system accompanied by soil disturbance 査読有り

Noda, T., Takeuchi, H., Nakai, K. and Asaoka, A.

Soils and Foundations 49 巻 ( 5 ) 頁： 739-756 2009年10月

*Numerical simulation of a delayed circular slip failure after the occurrence of the earthquake 査読有り

Nakai, K., Noda, T. and Asaoka, A.

Proceedings of 4th International Workshop on New Frontiers in Computational Geomechanics 頁： 29-32 2008年10月

担当区分：筆頭著者記述言語：英語

By using a soil-water coupled finite element method, deformation/failure behavior during and after the occurrence of an earthquake in a clay foundation-embankment system was numerically examined. The elasto-plastic constitutive model for the soil skeleton is the Super/subloading Yield Surface Cam-clay model. The embankment was calculated as a saturated soil. The results showed that the embankment maintained stability without any significant large deformation during the earthquake, while slip failure penetrating to the crest was suddenly generated a few hours after the earthquake.

Postseismic consolidation settlement of clayey soil due to the coseismic disturbance 査読有り

Noda, T., Takeuchi, H., Nakai, K., Nakano, M. and Asaoka, A.

Proceedings of 4th International Workshop on New Frontiers in Computational Geomechanics 頁： 57-60 2008年10月

*Delayed failure of a clay foundation-embankment system after the occurrence of an earthquake 査読有り

(6) Noda, T., Nakai, K. and Asaoka, A.

Theoretical and applied mechanics JAPAN 57 巻頁： 41-47 2008年

Liquefaction-induced consolidation of embankment soil after earthquake 査読有り

Asaoka, A., Sawada, Y., Noda, T. and Nakai, K.

Proceedings of 13th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering (13th ARC) 頁： 602-605 2007年12月

Effects of embankment rigidity on behavior of naturally deposited soils during/after earthquakes 査読有り

Noda, T., Asaoka, A, Nakano, M. Nakai, K. and Takeuchi, H.

Proc. of International Workshop on Earthquake Hazards and Mitigations 頁： 23-26 2007年12月

Structural re-upgradation in clay and sand accompanying plastic swelling 査読有り

Noda, T., Asaoka, A. Nakai, K. and Tashiro, M

Proceedings of 13th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering(13th ARC) 頁： 23-26 2007年12月

Explanation of cyclic mobility of soils: approach by stress-induced anisotropy 査読有り

Zhang, F., Ye, B., Noda, T., Nakano, M. and Nakai, K.

Soils and Foundations 47 巻 ( 4 ) 頁： 635-648 2007年8月

High ductility of structured clay and cyclic mobility of sand 査読有り

Nakai, K., Noda, T., Nakano, M., Tashiro, M. and Asaoka, A

Proc. of 3rd International Workshop on New Frontiers in Computational Geomechanics (IWS-Xian2006) 頁： 183-186 2006年

High ductility of structured clay and cyclic mobility of sand 査読有り

Nakai, K., Noda, T., Nakano, M., Tashiro, M. and Asaoka, A.

Proceedings of 3rd International Workshop on New Frontiers in Computational Geomechanics (IWS-XIAN 2006) 頁： 183-186 2006年

Large compression of soil due to decay of structure during drained repeated shearing 査読有り

Masaki NakanoAkira AsaokaKentaro NakaiMutsumi Tashiro

The 16th International Conference on Soil Mechanics and Geotechnical Engineering,Osaka, Japan. 頁： 929-932 2005年9月

記述言語：英語

Huge volume compression of loose sand can be easily observed not under monotonic loading but under repeated shear stress application with small amplitudes, which is called compaction of sand. Although it takes long time the similar phenomenon is commonly observed even in highly structured natural clay, which has been called, for long years, secondary consolidation/delayed compression of natural clay. This study describes that these large-scaled volume compression observed both in clay and sand is due to the decay/collapse of soil skeleton structure that occurs with on going plastic shear deformation. Distinguishing the mechanical difference between sand and clay, the super/subloading elasto-plastic constitutive model still explains the mechanism of the volume compression of soils consistently.

Densification/compression by compaction of a granular geomaterial changed by crushing dewatered sludge with air 査読有り

Kentaro NakaiMasaki NakanoKazuhiro Kaneda

The 16th International Conference on Soil Mechanics and Geotechnical Engineering,Osaka, Japan. 頁： 2307-2310 2005年9月

担当区分：筆頭著者記述言語：英語

To improve the construction surplus soil and to use the soil as a geomaterial, a densification technology of soil with high water con-tent such as dewatered sludge is studied. The densification is brought by the change from the `consolidation material' like clay to the `compactable material' like sand. The soil is crushed with air to an assembly of clay pebbles, the water content of which is ease to de-crease, and therefore the assembly can be compacted to high density without long consolidation time. The soil became low com-pressible and had high shear resistance, which can be describe by Super/subloading Yield Surface model.

高位構造を有する自然堆積粘土が示す塑性圧縮を伴う軟化挙動査読有り

中井健太郎中野正樹

応用力学論文集 8 巻頁： 451-460 2005年8月

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