The yield surface of granular matarials determined by the fabric in three-dimensional stresses

1)由织物确定的颗粒材料的屈服面几乎所有颗粒材料的屈服面都是由实验结果从现象学上确定的。然而，在本研究中，颗粒材料的屈服面是在微观结构的基础上提出的，由颗粒间接触法向的分布来评价，在二维应力状态下表示为（siguma_y， siguma_x和tau_y）空间，在三维应力状态下表示为一般应力空间。该方法可以很容易地解释在主应力值不变的情况下，由于主应力轴的纯粹旋转而产生的屈服。2)颗粒材料弹塑性模型的生成通过比较扩展Mises准则和SMP准则在主应力空间中的形状，提出了转换应力张量的方法。siguma_i的pi平面上的SMP曲线为圆形，变换后的主应力空间中的SMP曲面为圆锥体。将转换后的应力张量siguma_<ij>应用于Cam-clay模型和Sekiguchi-Ohta模型，将临界状态理论与SMP准则相结合。修正后的模型与Cam-day模型和Sekiguchi-Ohta模型具有相同的土壤参数，能够预测粘土在一般应力条件下的排水和不排水行为。因此，可以用转换后的应力张量siguma_<ij>代替普通应力张量siguma_<ij>，将其他仅在三轴压缩条件下有效的土弹塑性模型推广到一般应力条件。此外，通过引入新的硬化参数H，将修正模型扩展为粘土和砂土的统一弹塑性模型，该模型可以描述具有初始应力诱导各向异性（包括初始各向同性）的土体的负剪胀特性和正剪胀特性。

1) The yield surface of granular materials determined by the fabricAlmost all yield surface of granular materials have been determined phenomenologically by the experimental results. In this study, however, the yield surface of granular materials is proposed on the basis of the microscopic fabric which is evaluated by the distribution of interparticle contact normal It is expressed in (siguma_y, siguma_x and tau_y) space in the case of two dimensional stress state and in general stress space in the case of three dimensional stress state. The proposed method can easily explain the yield due to the pure rotation of the principal stress axis with the values of the principal stresses unchanged.2) Generation of elastoplastic model for granular materialsA transformed stress tensor has been proposed by comparing the shapes of the Extended Mises criterion and the SMP criterion in principal stress space. The SMP curve in the pi-plane of siguma_i is a circle and the SMP surface in the transformed principal stress space is a cone. The transformed stress tensor siguma_<ij> is applied to the Cam-clay models and the Sekiguchi-Ohta model to combine the critical state theory with the SMP criterion. The revised models, with the same soil parameters as the Cam-day models and Sekiguchi-Ohta model, are capable of predicting the drained and undrained behavior of clay in general stress conditions. Therefore, it is possible to extend any other elastoplastic models for soils, whose validity has been verified only in triaxial compression condition, to the general stress conditions by using the transformed stress tensor siguma_<ij> instead of the ordinary stress tensor siguma_<ij>. Moreover, the revised model is extended to be a unified elastoplastic model for clay and sand by introducing a new hardening parameter H, which can describe the negative and positive dilatancy characteristics of soils with the initially stress-induced anisotropy including the initial isotropy.