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

1)实验结果决定了颗粒材料的屈服面，几乎所有颗粒材料的屈服面都由实验结果唯象地确定。然而，在本研究中，颗粒材料的屈服面是基于颗粒间接触法线分布的微观组构提出的，它在二维应力状态下用(siguma_y，siguma_x和tau_y)空间表示，在三维应力状态下用一般应力空间表示。2)颗粒材料弹塑性模型的建立通过比较扩展米塞斯准则和SMP准则在主应力空间中的形状，提出了一种变换的应力张量。Siguma_i平面内的SMP曲线为圆，变换后的主应力空间中的SMP曲面为锥面。在CaM-Clay模型和Sekiguchi-Ohta模型中应用变换后的应力张量siguma&lt；ij&gt；将临界态理论与SMP准则相结合。修正后的模型具有与Cam-day模型和Sekiguchi-Ohta模型相同的土体参数，能够预测一般应力条件下粘土的排水和不排水特性。因此，只在三轴压缩条件下验证其有效性的任何其他土的弹塑性模型，都可以通过使用转换的应力张量siguma_&lt；ij&gt；而不是普通的应力张量siguma_&lt；ij&gt；来推广到一般应力条件。此外，通过引入一个新的硬化参数H，将修正后的模型扩展为粘土和砂土的统一弹塑性模型，该参数可以描述具有包括初始各向同性在内的初始应力各向异性的土体的正负剪胀特性。

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.