Study on the Strain localization behavior of water-saturated clay and the method of prediction

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It has been observed that geomaterials such as sand and clay deformshomogeneously in the early stage of loading and then the shear band occurs as a result of strain localization before failure. These phenomena have been well-known as the occurrence of slip surface and land slides. In order to describe and predict the failure phenomena of ground, it is quite necessary to clarify the mechanism of strain localization. In the present study, was studied a water saturated clay that is a difficult material to study because of the existance of pore water. Based on the experimental observations of shear bands during the undrained plane strain tests performed by multi-axial testing machine, the width and the direction of shear bands were discussed.Then, numerical simulations were carried out using the local and non-local viscoplastic constitutive model with strain softening. In the numerical analysis, the transport of pore water was included using the updated Lgrangian method and Biot'stheory of two phase materials. The following main conclusions were obtained :(1) Strain localization phenomena were numerically simulated by use of Adachi and Oka's viscoplastic constitutive model with strain softening.(2) The significant increase of the pore water pressure was observed along the shear bands. This trend is consistent with the experimentally observed results.(3) The shear bands develops significantly in the clay with small permeability.(4) The width of shear bands can be controlled by the second gradient of viscoplastic volumetric strain. The introduction of second gradient of viscoplastic strain make the material system more conservative.