Cyclic and anisotropic elasto-viscoplastic behavior of clay and constitutive model

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Natural soft clay was sampled at both Osaka and Akita by use of modified large diameter Laval sampler in which the angle of cutting edge was improved. Triaxial tests, torsional tests were performed under the undrained conditions, in addition, multiaxial tests were carried out under undrained plane strain conditions after isotropic consolidation. In the plane strain tests, it is observed that the stress path is quite different from the results for remolded clay samples. Immediate principle stress greatly varies during the deformation. In an early part of straining, b value changes in small amount and reaches about 0.5 at large strain. As for the cyclic elasto-viscoplastic constitutive model, the proposed model based on the non-linear hardening rule was discussed for the results of cyclic isotropic consolidation test. We have found that the proposed model is applicable to both cyclic shearing and cyclic isotropic compression. In the modeling, both linear and non-linear hardening are considered in order to prevent an over-ratcheting effect. In addition, an isotropic hardening rule are used with kinematical hardening rule to describe a deterioration of shear modulus.