Observation of bifurcation of geomaterial in 3-D conditions through triaxial test using rectangular specimens

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Clarification and predictions of strain localization of geomaterials are indispensable research topics to improve an accuracy of computation of the geotechnical engineering problems. Most of past numerical studies concerning the strain localization have been done under the plane strain conditions and most of experimental researches are done by the triaxial tests using cylindrical specimen or by the plane strain tests. With respect to the strain localization in the ground, large difference between two- and three-dimensional analyses exists. It is necessary to analyze ground under three-dimensional condition to consider the shear band formation. In the present study, in order to grasp the deformation and failure behaviors of geomaterials as true three-dimensional phenomena, the triaxial compression test using the rectangular clay specimen was conducted. The distribution of shear strain observed in side of specimen can be obtained by the image analysis of digital photographs.The results obtained are as follows.In the range of low strain level, the stain rate dependency behavior was observed as same as the conventional triaxial test of clay even though the rectangular specimen was used. The strain rate affected deformation pattern of specimens ; lower strain rate tests had more significant strain localization on the surface of specimens, in particular the normally consolidated clay specimens. However, overconsolidated clay specimen had wider area which strain localization was observed. The final deformation patterns were closely related to the shape and scale of specimens rather than the consolidation conditions.In the stress - strain relations, the strain softening were more clearly observed in the specimens, which deformed like buckling column. On the contrary. the significant strain softening were hardly occurred on stress - strain relations in the case of the specimen, which several shear bands existed and crossed each other.