10 巻 (2007) p. 281-292
Deformation behaviors of soil specimens, such as strain localization and formation of shear band with some geometric patterns, are very complex and quite diversified. Recently, experimental failure behaviors of soil deformation have been extensivelystudied with the aid of image processing techniques such as stereophotogrammetry. This research aims to capture these failure behaviors of soils from a viewpoint of diffuse bifurcation, which engenders non-homogeneous or localized deformation from a homogeneous state. FE-basednumerical bifurcation analysis and plane-strain biaxial experiments on sand by ALERT-Geomaterials are compared to provide a clear insight into the complex phenomena in soil deformation. Fully nonlinear finite deformation FE-analysis with Cam-clay or Drucker-Prager plasticity models formulated in the framework of the multiplicative finite strain theory is utilized to simulate the soil deformation. Analysis results reveal that such complex failure modes of soils are arguably caused by clustered bifurcation points and repeated occurrences of the diffuse mode bifurcations. Moreover, these analyses quantitatively well estimate the location of the bifurcation points and the degradation and oscillation of stress in the post-bifurcation regimes.