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

采用改进的大直径拉瓦尔取样器对大阪和秋田的天然软土进行了取样，该取样器改进了切削刃的角度。在不排水条件下进行了三轴试验、扭转试验，并在各向同性固结后的不排水平面应变条件下进行了多轴试验。在平面应变试验中，观察到应力路径与重塑粘土样品的结果有很大不同。变形过程中直接主应力变化很大。在应变初期，b值变化不大，大应变时达到0.5左右。对于循环弹粘塑性本构模型，针对循环各向同性固结试验结果，讨论了基于非线性硬化规律的循环弹粘塑性本构模型。结果表明，该模型既适用于循环剪切，也适用于循环各向同性压缩。在建模中，为了防止过度棘轮效应，考虑了线性和非线性硬化。此外，采用各向同性硬化规则和运动硬化规则来描述剪切模量的劣化。

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.