Study of shear bands and prediction of compaction and failure in the strain localization behavior of geomaterials

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ABSTRACT: Strain localization problems such as shear bands and slip surfaces are very important because those are precursor of failure. Hence many researchers have been studying for the last 30 years. On the other hand, compaction bands have been studied in recent years for the analysis of large settlement of off shore structures. In fact, experimental work on porous geomaterials has been done from 90s. A series of triaxial compression tests under the drained conditions was performed on diatomaceous porous rocks. A rectangular-shaped prismatic specimen was used to easily measure the strain distributions on the specimen surface. The distributions of local strain, i.e., shear strain, axial strain, and volumetric strain, were measured on the surface of the specimen by using an image analysis technique newly developed for this experiment. After the shear testing, the changes in density of the specimen were measured by an X-ray CT scanner. Some high density regions were found to correspond to the compaction bands observed in the image analysis in the cases of relatively high confining pressure levels. Then, we have carried out a numerical simulation of sensitive clay using an elasto-viscoplastic model with structural degradation based on the finite deformation theory, and we have found the compressive strain localization during the consolidation process. In addition, using the same model, numerical simulations of consolidation of soft clay and drained triaxial tests of diatomaceous mud stone have been carried out to study the compressive localization, namely, compaction bands and strain localization of geomaterials was discussed.