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No.52 (2005/12) >

Title :接線・下負荷面モデルによる土の比例負荷および非比例負荷挙動中表現
Authors :瀬戸内, 秀規
Authors alternative :Setouchi, Hideki
Issue Date :1-Dec-2005
Abstract :本論文は,降伏面の内部の応力変化による塑性変形を表現し得る非古典弾塑性論としての下負荷面モデルに下負荷面の接線方向の応力速度成分つまり接線応力速度による非弾性ひずみ速度を考慮した接線・下負荷面モデルを比例負荷から繰返し非比例負荷に至る広範の負荷を受ける地盤材料の変形挙動の予測に適用し,実測値と比較することにより本モデルの妥当性を検証したものである.まず,砂における3軸試験装置で得られた排水および非排水条件の繰返し試験,真の3軸試験装置および中空捩り試験装置で得られた排水条件の繰返し等方圧縮,軸対称圧縮およびb-値一定の圧縮・伸張試験,および非比例負荷である真の3軸試験装置で得られた排水条件の平均主応力一定繰返し円形応力負荷試験のシミュレーションを行った.一連のシミュレーション結果から,本モデルが負荷条件によらず地盤材料の変形挙動を統一的に予測できることを実証した.また,円形応力負荷では,負荷過程における非弾性ひずみ速度の方向および大きさを明らかにすることにより,従来の弾塑性構成式は応力速度方向の剛性を非現実的に高く予測することを示し,接線・下負荷面モデルは接線応力速度による非弾性ひずみ速度により応力速度方向の剛性を適切に緩和でき変形挙動の予測精度を向上させることを実証した.さらに,土の異方性を表現する下負荷面の回転を考慮したモデルおよび接線応力速度によって誘導される接線ひずみ速度の方向が下負荷面の接線方向のみでなく下負荷面の外向き法線方向を有するとする拡張接線・下負荷面モデルを導入し,砂の応力プルーブおよび主応力軸回転試験に適用した.その結果,下負荷面の回転の効果を明らかにするとともに,接線応力速度による下負荷面の外向き法線方向の非弾性ひずみ速度の効果によりさらに高精度に非弾性ひずみ速度を予測できることを示し拡張接線・下負荷面モデルの妥当性を実証した.
The inelastic strain rate described in the traditional elastoplastic constitutive equation is independent of the magnitude and the direction of stress rate component tangential to the yield surface. Therefore, an unrealistically high stiffness modulus is predicted for nonproportional loading process significantly deviating from proportional loading. The tangential-subloading surface model can describe not only the plastic strain rate due to the stress rate component normal to the subloading surface but also the tangential strain rate due to the stress rate component tangential to the subloading surface. The major advantage of this model is that the model is not restricted to materials obeying isotropic hardening/softening law and also for materials having a simple isotropic shape of loading surface. Further the model is applicable to arbitrary loading conditions including cyclic loading, since the model is based on the subloading surface model and fulfills the mechanical requirements for cyclic plasticity. The validity of the tangential-subloading surface model for the prediction of soil deformation behavior is studied in this research. The model is based on the extended subloading surface model incorporating the evolution rule of the similarity-center of the normal-yield and the subloading surfaces with the rotational hardening and the isotropic and the deviatoric hardenings. The predictions is compared with the test data of sands subjected to various loadings ranging from proportional to cyclic nonproportional loading, while the unique sets of material parameters are used, and the calculations are performed from the unique initial states in spite of the variety of test types. Further, the concepttangential stress rate relaxationon the relaxation relevant to the deviatoric part of the component of stress rate tangential to the subloading surface is applied for the prediction of deformation behavior of soils subjected to stress probe and principal stress axes rotation. The validity of the concept is verified by comparing with the test data. Then, it is concluded that the tangential-subloading surface model can simulate reasonably well the arbitrary loading behavior including cyclic nonproportional loading and the concept of the tangential stress rate relaxation is of importance for describing more realistically nonproportional loading behavior.
Type Local :紀要論文
ISSN :0370-4246
Publisher :琉球大学農学部
URI :http://hdl.handle.net/20.500.12000/3334
Citation :琉球大学農学部学術報告 = The Science Bulletin of the Faculty of Agriculture. University of the Ryukyus no.52 p.49 -126
Appears in Collections:No.52 (2005/12)

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