地盤解析にみる分岐概念と非共軸性を考慮した構成方程式の工学的意義

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This paper describes bifurcation concept in geotechnical analysis and the technological significance of a non-coaxial constitutive equation of clay.
In unconfined compression tests, deformation of specimen is uniform in the early stage of loading. Deformation changes from uniform deformation to non-uniform deformation near maximum load. As that time localization of strain leads to failure of specimens through formation of shear bands. Therefore, signs of failure appear before destruction. Bifurcation analysis gives the bifurcation stress ratio, i.e., stress ratio at the onset of non-uniform deformation. Design and construction of civil engineering works using bifurcation stress ratio is safer than using stress ratio at failure.
By incorporating non-coaxiality into the clay model, Both current stresses and current stress rates influence plastic strain. Consequently, clays become easy to simple-shear. Bifurcation stress ratios became small when the clay model incorporating non-coaxiality was used for bifurcation analysis to model deformation of clay under plane strain undrained loading. Deformation analysis which models construction of earthfill on the soft ground using the clay model demonstrates clear transition from localized strain to fomation of shear bands.