Elasto-Viscoplastic constitutive model for natural clay and its application

为了合理地分析天然粘土堆积体的变形，建立天然粘土的本构模型是非常重要的。为此，我们首先对天然粘土进行了几种试验，如各向异性固结试验、利用三轴仪进行的不排水压缩和拉伸试验以及不排水条件下的扭转空心筒试验。根据这些结果，我们找到了超固结边界面(初始屈服面)，并考察了本构模型中粘塑性参数的变化。此外，还阐明了剪切特性的速率敏感性和软化特性。通过对预压试件的三轴试验结果，观察了扰动对其力学行为的影响；从主应力面与水平层面倾角不同的试件的三轴试验结果中发现，结构各向异性对变形行为的影响比超固结东大阪粘土的b值更为显著。在此基础上，建立了描述超固结区天然粘土循环特性和各向异性特征的粘弹塑性模型。并讨论了该模型在实际边值问题中的应用问题。

In order to rationally analyze the deformation of natural clay deposits, it is very important to construct constitutive model for natural clay. For this purpose, firstly we have carried out several tests for natural clay, e. g. anisotropic consolidation test, undrained compression and extension tests by use of triaxial apparatus and torsional hollow cylinder tests under undrained condition. From these results, we have found the overconsolidation boundary surface (initial yield surface) and examined the variation of viscoplastic parameters in the constitutive model. Also, rate sensitivity and softening characteristics of sheer behavior have been clarified. By the triaxial tests results for the presheared sample, the effect of disturbance for the mechanical behavior was observed.From the triaxial test results on the samples with different inclination angle between the major principle stress plane and the horizontal bedding plane, it was found that the effect of structural anisotropy on deformation behavior is more marked than the b value in the overconsolidated Eastern Osaka clay.Considering the above mentioned experimental results, we have developed an elasto-viscoplastic model for clay which can describe the cyclic behavior and anisotropic characteristics of natural clay in the overconsolidated region. And we have discussed the problem of application of the proposed model to the real boundary value problem.