Constitutive model for soil considering induced and inherent anisotropy

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Soil deposits have anisotropy in nature. However, most of elastoplastic constitutive models for soils do not take into anisotropy, because these are formulated on the basis of isotropic hardening theories. Investigating the anisotropic behavior of sand and clay, we formulated constitutive models for sand and clay in which soil anisotropy could be taken into account properly.Anisotropy of clay was investigated on the basis of undrained triaxial tests and direct shear tests on natural clay and one-dimensional consolidated clay. The observed anisotropic behavior was uniquely analyzed using a kinematic hardening model for clay in which stress induced anisotropy was taken into consideration. On the other hand, it was experimentally shown that anisotropy of deposited sand was different from that of clay, and the main cause of anisotropy was inherent anisotropy. An elastoplastic model for sand incorporating the fabric anisotropic tensor was able to describe well the anisotropic stress-strain relationship and strength in isotropic compression, triaxial compression and plane strain tests on deposited sand.