【作者】 何青峰；

【导师】 赵法锁； 肖平新；

【作者基本信息】 长安大学 ， 地质工程， 2008， 博士

【摘要】 黄土是一种具有地域性分布的特殊土体,其物理力学性质随地域不同而具有显著的差异。本文以延安Q₂黄土为研究背景,以黄土的结构性和流变特性为研究的核心内容,通过对不同含水量延安Q₂黄土进行常规物理特征试验、单轴无侧限压缩试验、常规三轴压缩试验、单轴蠕变试验、扫描电子显微镜观测以及三轴蠕变试验研究,运用力学分析和数值分析等方法对延安Q₂黄土的力学参数及结构损伤特征随含水量的变化规律、剪切变形破坏特征、蠕变变形破坏特征以及本构模型等进行了系统的研究,本研究工作对黄土高原地区的各类岩土工程设计有着重要的理论和实践意义。本文的主要成果有:（1）通过常规物理性质试验研究了延安Q₂黄土的颗粒组成、矿物成分等;通过单轴无侧限压缩试验和常规三轴压缩试验研究了黄土的结构强度、粘聚力c以及摩擦系数tanφ等力学参量随含水量的变化规律。（2）CU剪切试验表明,Q₂黄土的应力应变关系呈强软化型至较强软化型,该本构关系可用刘祖典教授（1996）提出的强软化型本构模型来描述。依据试验结果深入研究了模型参数随含水量和围压的变化规律,讨论了应变速率对黄土应力应变曲线的影响情况;总结了黄土剪切破坏的整体变形方式、破坏类型和变形破坏力学模式。（3）单轴压缩试验中,延安Q₂黄土的应力损伤门槛值随含水量的增加呈指数函数减小,而黄土的应变损伤门槛值与含水量的关系不大,初始弹性模量随含水量的增加呈幂函数降低。采用刚度损伤和强度损伤假设及统计损伤方法,求取了宏观参量和微观结构变化的黄土损伤变量表达式,分别建立了黄土刚度损伤、强度损伤和统计损伤本构模型,并比较了各模型的特点。（4）大量蠕变试验结果表明,延安Q₂黄土单轴蠕变破坏应力随含水量的增加呈指数函数减小,相同含水量条件下蠕变破坏应力与结构强度的比值约为0.8;三轴蠕变试验中含水量和围压对黄土蠕变破坏应力有着很大的影响,依据试验结果研究了黄土蠕变破坏应力随含水量和围压的变化规律;总结了三轴蠕变黄土的整体变形及破坏特征。（5）通过对延安原状Q₂黄土和单轴蠕变破坏黄土进行扫描电子显微镜观测发现,蠕变前原状黄土的结构以支架大孔隙胶结结构和镶嵌微孔隙胶结结构为主,蠕变后则转为以镶嵌微孔隙胶结结构和凝块状胶结结构为主,黄土蠕变过程的实质就是随着外荷载的增加土体颗粒结构连接由结构硬化逐步转变为结构软化的过程。（6）依据蠕变试验结果,运用Riemann-Liouville型分数阶微积分算子理论探索性地建立了黄土软体流变本构模型,并对模型参数变化规律进行了研究;运用模型理论建立了黄土的粘弹塑性流变模型,在此基础上引入统计损伤理论建立了考虑瞬时损伤的黄土统计损伤流变本构模型和能反映黄土加速蠕变阶段的蠕变损伤流变本构模型。（7）采用ANSYS进行前处理,用APDL语言提取计算所需的相关信息,用MATLAB6.5编制了Q₂黄土粘弹塑性损伤流变模型的平面应变有限元计算程序。利用编制的有限元程序,对延安Q₂黄土蠕变试验进行了有限元分析,结果表明该模型可以较好的反映黄土的流变特性。更多还原

【Abstract】 The loess is a special kind of regionally distributed soil whose physical mechanics nature varies significantly in different regions. Taking the Q₂ loess of Yan’an as the researching material while focusing on the structural and the rheological properties of the loess, this paper has carried on a series of research tests and experiments, namely, the conventional physical feature test of the Yan’an Q₂ loess with different water content, the conventional unaxial compression test, the conventional triaxial compression test, the unaxial creep experiment, the observation through scanning electronic microscope as well as the triaxial creep experiment. A systematic research has also been conducted on Q₂ loess, through mechanics analysis and numerical analysis, to discover the mechanics parameters and the law of the characteristic change of the structural damage due to the change in the water content, and the destruction characteristics of detrusion and total creep, the constitutional model, and so on, which has an important theoretical and practical significance on the designing of ground projects of all kinds on the Loess Highlands area.The main achievements of this paper include:（1） Researching into the basic physical target characteristics of the granular compositions and the mineral components by way of the conventional physical feature test, researching into the law of change of mechanics parameters （mainly include structure strength of the loess, the cohesive force, the friction coefficient） owing to the change in water content.（2） It is indicated from the CU shear test that stress-strain relations of the Q₂ loess assume the strong conditioning to the stronger conditioning. This construction relation can be described by the strong conditioning model proposed by Professor Liu Zudian （1996）. Discussions have also been conducted about the law of the change of those model parameters with the change in the water content and confining pressures, and about the influences of the strain speed on the stress-strain curve based on the results of the test. Summaries have been reached on the whole distortion way due to the loess shearing destruction, the type of destruction and the mechanics pattern of the distortion destruction.（3） The unaxial compression test indicated that stress damage threshold value of Yan’an Q₂ loess decreases exponentially with the increase in water content, while, the damage strain threshold value of the loess has little relation with the water content, and the initial elasticity module decreases by power function with the increase in the water content. By means of the assumption of the rigidity damage and the intensity damage and statistical method of measuring the damages, this research paper seeks for the expressions of the macroscopic parameters and the microscopic structure change for the loess damage, and establishes models of rigidity damage, intensity damage and statistical damage of the loess, and compares the features between these models.（4） It is indicated from the result of a massive amount of creep tests that the unaxial failure stress of the Yan’an Q₂ loess decreases exponentially with the increase in the water content, the ratio of the creep failure stress to structural intensity under the same water content is approximately 0.8; while in triaxial creep test, the water content and confining pressure have tremendous influence on the creep failure stress of the loess. Based on the testing result, it is also discussed the law of the change in the creep failure stress of the loess with the changes in water content and confining pressure. The whole distortion characteristics and shape of the triaxial creep leoss have been summarized as well.（5） It is indicated through the observational analysis by scanning electronic microscope into the Yan’an original Q₂ loess and the unaxial creep damaged loess that the structure of the original loess is featured primarily, before the creeping, by supportive megapore cemented structure and mosaic micropore cemented structure, while after the creeping it transfers to the micropore cemented structure and congeal cemented structure primarily. The essence of the loess creep process is that the soil granular structure connection is changing, with the increasing in the outside load, from structure hardening to structure conditioning.（6） Based on the result of the creep test, the soft rheological constitutional model is established exploratorily through the Riemann-Liouville score step calculus operator theory, and the changing law of the model parameters has been explored as well. The visco-elasticity-plasticity rheological model of the loess is established by the modeling theory; with this basis , two kinds of rheological constitutional models are established, one considers loess statistical damage caused by instant damages by introducing statistical damage theory, and the other considers creep damages while the loess accelerating creep process can be well reflected.（7） This paper carries out the preprocess using ANSYS, gets related information needed in computing by the APDL language, and compiles the plane strain finite element computational program with MATLAB6.5 language. By using the established finite element program, finite element analysis is carried out on the creep test of the Yan’an Q₂ loess whose result shows that this model can well reflect the rheological characteristics.更多还原