Mechanism of shear band formation in Ko-consolidated clayey soil--experimental and theoretical approaches by naked hollow-cylindrical soil specimen--

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The purpose of this research is to give theoretical and experimental bases to capture the failure mechanism of the ground material. The development of localized deformation and its prominence may cause the instability of foundation ground and lead to its failure. Such localized deformation is commonly observed during large deformation of soils, for instance, slip lines observed in the laboratory, the sliding failure of embankment foundation and the fault caused by the orogenic movement. The simulation of shear bands formation may lead to clarify the occurrence mechanism of their phenomena and also make it possible to explain the soil behaviors consistently from the beginning of deformation up to the limit failure state.In this research, the theoretical basis of bifurcation problem is summarized and classified in regard to the formation of shear band. In particular, the mathematical conditions of the formation of shear band under axisymmetric condition discussed relating to the non-coax … More iality of the elasto-plastic constitutive model for Ko-consolidated clay specimen proposed by Sekiguchi and Ohta (1977). As to experimental study, a new shear test equipment is designed and developed to observe the development of shear band with increase of shear strain in the axisymmetric soil specimen. The distinctive features of it are : 1) able to carry out Ko-consolidation, 2) able to measure Ko-value, 3) able to observe the development of shear bands (slip lines), because a rubber membrane is not used (naked specimen like the unconfined compression test specimen), 4)able to estimate parameters in terms of effective stresses, because the pore water pressure can be measured using measurement system of negative pressure with the ceramic disk.It was found in this research that the apparent strain-softening stress strain relation in axisymmetric soil specimen is not an essential phenomenum of material but the consequence of inhomogeneous distribution of stress and strain in the specimen as a boundary-value problem. Less