【作者】 张坤勇；

【导师】 殷宗泽；

【作者基本信息】 河海大学 ， 岩土工程， 2004， 博士

【摘要】 应力诱导各向异性是土体的重要特性，也是土体材料不同于金属材料的一个典型特性，并且在很多土体工程中都普遍存在这种因为应力状态改变而导致土体各向异性的现象。如何正确的在土体本构关系的研究中模拟、反映这种应力各向异性的影响，尝试突破现有传统理论中各向同性假设所带来的实践和理论上的限制，建立能够反映这种特性的土体本构模型，对于土体本构关系的研究具有重要的理论意义，同时对于解决工程实际问题提供新的思路和解决途径，对岩土工程实践有相当的实际意义。 本文首先在河海大学ZSY-1真三轴试验仪上进行了主要针对砂土的系列不等向固结后单向加载试验。通过对装样方法的试验验证，表明振捣湿法装样可以有效消除制样所引起初始各向异性的影响；在前人试验的基础上，进一步验证和揭示了土体在复杂应力状态下的各向异性应力变形规律；为建立各向异性模型提供了试验依据。通过对真三轴试验和相关资料试验结果分析比较，表明在三向应力状态下，土体这种非连续介质散粒体材料具有典型的应力各向异性； 在复杂应力状态下土体真三轴试验揭示的出土体各向异性基本规律基础上，从柔度矩阵的角度分析各向异性的影响，总结了复杂应力状态下柔度矩阵应该具有的特征，同时对现有模型的局限性进行深入分析；提出应力各向异性是土体这种散粒体非连续介质材料区别于一般典型弹性连续介质材料的根本特性之一 考虑各向异性特点，从实用角度出发，对既有常用的土体非线性弹性本构模型的深入分析；在常用经典非线性弹性模型—邓肯E-v非线性弹性土体本构模型基础上，结合真三轴试验结果所揭示的复杂应力条件下土体应力各向异性特性，建立一种近似的实用各向异性非线性弹性模型，从而从一定程度上反映土体应力各向异性的影响 结合坐标转换方法，通过适当假设，给出各向异性模型在一般应力空间的应力应变关系转换矩阵，推导了平面问题的各向异性有限元格式；在河海大学BCF固结有限元程序的基础上，通过添加各向异性模型的相应程序段，编制了各向异性固结有限元计算程序，对一简单算例进行了数值计算分析，并和邓肯E-v模型计算结果进行比较，结果初步验证了各向异性模型和程序的可靠性。 依据本文各向异性模型和平面固结有限元程序，对某面板堆石坝进行平面应力变形分析，并和常规邓肯模型计算结果及现有实测资料比较，分析了各向异性对于面板堆石坝应力变形的影响；通过分析蓄水期间面板堆石坝的加荷特征，说明在此阶段在坝体内由于应力各向异性的影响，坝体材料的应力应变规律和常规模型有所不同，并将对坝体应力变形特征，尤其是面板上的变形和应力分布规律产生显著影响。现有模型因为不能合理考虑这种应力各向异性的影响，采用了较大的泊松比和较小的弹性模量，计算出的面板拉应力分布区域和数值大小和现有的实测资料比较，都普遍偏大。本文提出的各向异性非线性弹性模型能从一定程度上考虑这样各向异性的影响，计算的面板应力变形规律更符合实际规律； 用各向异性模型对某土质心墙坝进行应力变形有限元计算，并和常规邓肯模型结果比较，分析说明各向异性对于高土质心墙坝水力劈裂评估效果存在影响；复杂加荷条件下，如土石坝蓄水阶段，由于土体加荷方式和常规三轴试验中的轴向加荷方式不同，水荷载是从小主应力作用方向施加，土体中存在应力诱导各向异性;各向同性模型不能考虑这种影响，导致对心墙水力劈裂进行评估结果可能偏危险;各向异性模型结果较邓肯E-v模型有所改善。 鉴于土体本质上的弹塑性特性，以及弹塑性模型在土体本构理论研究中的重要地位，本文在前人研究的基础上，以剑桥模型为基础，借鉴关口太田模型的建模思想，通过在修正剑桥模型中引入新的应力比参数，初步尝试建立各向异性弹塑性模型。将关口太田模型的弹头形屈服轨迹修正成为椭圆形屈服轨迹以适应等向固结应力路径;通过调整弹性区的范围，改善关口太田模型过大的计算变形。用修正后的各向异性弹塑性模型对一简单算例作有限元计算，结果比较说明修正后模型的计算变形有所改善。关键词:土体本构关系应力各向异性真三轴试验柔度矩阵有限元更多还原

【Abstract】 Stress-induced anisotropy is one of very important characters of soil and also key difference from metal material, which exist in many geotechnical projects. It is very important to stimulate and reflect the anisotropy in the process of study on soil’s constitutive relationship. To establish a reasonable anisotropic constitutive model will supply some new methods to solve some practical problem. Study on the stress-induced anisotropy is very important in terms of theoretical analysis and practical engineering.Based on series true-triaxial tests under complex stress state, basic anisotropic deformation mechanism and mechanical characteristics of soil is discovered, which will supply enough data for the establishment of anisotropy constitutive model. Based on the test results, the main character of the strain-stress matrix of soil under complex stress state is summarized. It is summarized that the shape and form of the strain stress matrix of soil elements under complex stress state, which may be used to verify and check the correct and rationality of soil’s constitutive model.By considering the stress-induced anisotropy under complex stress state, based on the usual-used Duncan-Chang model, a new anisotropic model is developed, which can describe the stress-induced anisotropy and is convenient by applying the same parameter as Duncan-Chang model.To apply the new model in the FEM, the coordinate transformation method is discussed. The anisotropic finite element format of planar is derived. By making some necessary changes to the BCF FEM codes, an anisotropic 2D FEM program is given, which apply the new anisotropic model. A simple example is analyzed and it is shown that the anisotropic model is superior to conventional non-linear elastic model on aspect of reflecting the anisotropy and the program is reliable.Compared with conventional Duncan-Chang E-v and E-B model, the anisotropic model was applied to perform the 2D Fern analyses on the practical rockfill dam. The results showed that conventional model couldn’t stimulate the stress-induced anisotropy produced during the process of reservoir impoundment, which will bring major error of stress and displacement calculation in the concrete faceplate and also will influence the hydro fracture in the earth core rockfill dam. Anisotropy model can stimulate this character to some extent. A new elastic-plastic model is also presented based on the Cam-clay model with the consideration of initially stress anisotropy. This model was developed by modifying the Sekiguchi-Ohta model using a new stress parameter and adjusting the yield locus and hardening axis in the p-q plane, which will improve the calculated results. A simpleexample is analyzed by FEM with the new model. The result is compared with that got from Cam-clay model and Sekiguchi-Ohta model; it is shown that new anisotropic model is superior to original model.更多还原