The Development of Consitutive Equation under General Stress Condition for Sands Anisotropic Deformation-Failure Behaviors due to Initial Structure and Stress History

总结两年来的研究成果如下：1.建立了砂土三维变形破坏本构模型。该模型称为多向滑动模型。(A)该模型的基本概念是，砂土等颗粒材料本质上是离散的，在所有位置和方向上都有无数潜在的滑动面，其变形特性受每个滑动面上的滑动机制所支配。(B)每个滑动面上考虑了三种变形机制：压缩变形、剪切变形和剪胀变形。(C)模型参数的取值可以根据常规三轴试验中观察到的变形行为来确定。该模型适用于各种应力条件，并通过观测到的变形破坏行为进行了验证。(A)该模型适用于包括应力轴旋转在内的一般应力条件，并能考虑围压和超固结的影响。(B)该模型可以模拟砂土变形破坏行为的固有各向异性和诱发各向异性：前者是由砂粒形成的各向异性初始结构引起的，后者是由剪应力历史引起的。将该模型引入到边值问题的有限元方法中。将该计算方法应用于浅基础承载力问题，结果表明：(1)该模型能较好地预测初始各向异性结构地基的荷载-位移特性和变形特性.(2)由于模型考虑了围压对砂土单元抗剪强度的影响，计算方法较好地预测了地基宽度对承载力的尺度效应.

The results of the research during two years are sunmmarized as follows :1. The constitutive model for three-dimensional deformation-failure behaviors of sands was developed. The model is named 'Multi-Directional Slinding Model'.(a) The basic soncept of the model is that granular materials such as sands are essentially descrete and have innumerable potential sliding planes in all locations and in all directions, and its deformation characteristics are governed by the slidin13EA\ : g mechanisma on each sliding plane.(b) Theree types of deformation mechanisms are considered on each sliding plane : compression, shear deformation and dilatancy.(c) The values of model parameters can be determined from the deformation behabiors observed in conventional triaxial tests.2. The model was applied to various stress conditions, and was verified by the observed deformation-failure behaviors.(a) The model is applicable to the general stress conditions including the rotation of stress axs, and can take the effects of confining pressure and overconsolidation into account.(b) The model can siulate the inherent and induced anisotropies in sands deformation-failure behaviors : the former is due to the anisotropic initial structures formed by sand grains and the latter is due to the shear stress history.3. The model was incorporated to the finite element method for boundary value problem. The calculation method is applied to the bearing capacity probles of shallow footing.(a) It was found that the model can predict the load-displacement behaviors and deformation properties of graound with initial anisotropic structures.(b) The scale effect of footing width on bearing capacity was predicted propwerly by the calculation method, becouse the effect of confining pressure on shear strength of sand element is taken into account by the model.