【作者】 颜斌；

【导师】 倪万魁；

【作者基本信息】 长安大学 ， 岩土工程， 2010， 博士

【摘要】 本文以前人对洛川黄土剖面土层的研究资料为基础,从宏、细、微观研究方法入手,通过土工常规实验、高压固结试验、三轴剪切试验、激光粒度分析、电镜扫描和CT扫描试验,对洛川剖面黄土的粒度组成、物理性质指标、微结构类型、结构性参数、压缩(湿陷)性、结构强度和抗剪强度进行了系统研究。从沉积环境和应力历史定性分析了黄土物理性质和微结构的关系及其在剖面上的差异性,以结构性参数和结构强度定量研究为基础,重点分析了结构性参数与黄土压缩性(湿陷性)以及结构强度与抗剪强度的相互关系,并基于土的微结构模型和广义有效应力原理,揭示了黄土结构压缩破坏和剪切破坏的力学机理,为结构性黄土压缩沉降变形的计算和抗剪强度参数的选取及稳定性分析提供了新的研究思路,对解决黄土工程问题具有重要的理论和实际意义,也促进了土结构性理论的发展和应用。取得的主要研究成果如下：(1)对洛川剖面黄土的粒度组成、孔隙特征、微结构和主要物理指标的试验研究表明,各层黄土的粒度组成以粗粉粒为主(含量大于50%),整体剖面上粒度比较均匀,不存在明显的粒度分异现象,而黄土微结构在剖面上的差异性主要受沉降环境和应力历史的影响。Q4、Q3新黄土以支架大孔微胶结和支架大孔半胶结为主的结构特征反映了干冷的气候环境和低应力下较短的沉积历史的共同作用；Q2老黄土以镶嵌微孔微胶结和镶嵌微孔半胶结为主的结构特征反映了高应力下的较长沉积历史是其主要影响因素,而干冷气候环境影响较小；Q2古土壤以絮凝状胶结和凝块状胶结为主的结构特征反映了湿热的气候环境和高应力下的较长沉积历史的共同作用。黄土物理性质指标和微结构类型在剖面上的变化具有很好的对应性,反映出黄土的结构对其工程性质具有控制作用。(2)通过高压固结试验,定量分析了各层黄土的应变综合结构势参数与含水量的关系,表明洛川剖面黄土从上到下(从新到老)其水敏性逐渐减弱。提出了基于应力的结构可稳性系数、结构可变性系数和应力综合结构势的定义和求取方法,重新定义了超固结比概念,并运用这些新概念、新方法对洛川剖面黄土的结构稳定性和固结状态进行了定量评价,结果表明Q4、Q3新黄土的结构稳定性差,处于欠压密状态,而Q2老黄土的结构稳定性相对较好,处于正常固结或轻超固结状态。上述研究结果与黄土的微结构特征和工程实际是一致的。(3)基于应变综合结构势的概念,推导出结构性参数与湿陷系数、水敏性系数与压缩系数的关系式,并定量分析了洛川剖面黄土的结构性参数与水敏性参数的变化规律。根据黄土三相物质的相互作用原理,提出了黄土微结构的概念模型,建立了非饱和黄土的广义有效应力模型,基于这些模型解释了黄土欠压密性和结构压缩破坏的力学机理,并探讨了结构性黄土固结沉降变形的计算方法。(4)运用土的抗剪强度理论,推导出结构强度的计算公式,建立了结构强度与抗剪强度的关系式,并通过原状黄土与重塑黄土的三轴剪切试验,定量分析了黄土结构强度和抗剪强度在剖面上的变化规律及其与含水量的关系,建立了原状黄土和重塑黄土的抗剪强度参数(粘聚力、内摩擦角)与含水量的拟合关系,探讨了以重塑土抗剪强度参数近似求取原状黄土强度参数的方法,为解决原状黄土三轴试验数据离散、强度参数变异性较大的问题提供了新的途径。同时基于三轴剪切的p-q应力路径,分析了黄土结构剪切破坏的力学机理。(5)通过黄土三轴剪切CT扫描试验,对初始、固结以及剪切过程中的CT数、损伤变量以及黄土细观结构损伤演化进行了全过程分析,运用损伤力学原理,建立了具有尺度效应的黄土结构损伤变量演化方程,并基于CT图像处理对三轴剪切过程中黄土细观结构损伤和硬化屈服的物理机制进行了量化分析。更多还原

【Abstract】 Based on the previous academic research of Luochuan loess profile, this paper is considered from macroscopic, mesoscopic and microscopic ways,and systematically studied grain-size composition, physical property index, type of microstructure, structural parameter, compressive (collapsible) property, structural strength and shear strength of loess profile in Luochuan by means of routine soil test, high pressure consolidation test, triaxial shear test, laser particle size analysis technology, electron microscopic scanning and CT scanning tests. First, we qualitatively analyze the relationships between loess physical properties and microstructure under different sedimentary environment and stress history, and the differences on loess profiles. Following, on the basis of structural parameter and structural strength quantitative study, this paper focuses on the correlation between loess structural parameter and compressive (collapsible) property, and between structural strength and shear strength. The last but not the least, applying the model of soil microstructure and the principle of general effective stress, we reveal the mechanical mechanism of loess structural compressive failure and shear failure, which provides a method for profound study on the calculation of loess structural compression deformation, chosen of shear strength parameter and analysis of stability. So there is important academic significance and application value on solving loess project problem, and much contribution to the research and application of soil structure theory. The main contributions are as follows:(1) We take tests about grain-size composition, pore structural characteristics, microstructure and major physical property index. Result shows that the grain size of each layer is mainly coarse silt (content more than 50%), scattering in a fairly equal manner and showing no evident of grain size distribution. However, the differences of loess microstructure on the profile contribute to the sedimentary environment and stress history.The structure of Q4, Q3 neo-loess presents the bracketed-macropore weak-cemented structure and half-cemented structure characteristics, which reflects the result of interaction of dry and cold climate and short sedimentary history with low stress.The structure of Q2 old loess presents the inlaid-micropore weak-cemented structure and half-cemented structure characteristics, which reflects the material effect by long sedimentary history with high stress, while the tiny effect by dry and cold climate.The structure of Q2 paleosol presents the flocculated-cemented structure and clotted cemented structure characteristics, which reflects the result of interaction of wet and hot climate and long sedimentary history with high stress.There is a perfect correspondence between loess physical property index and microstructure along with the change on the profile, illustrating that loess’structure controls its engineering properties.(2) From high pressure consolidation test, we quantitatively analyze the relationship between the parameter of strain comprehensive structure potential (strain-CSP) and content of water for each loess layer. It finds that the deeper the loess profiles, the weaker the water sensitivity of Luochuan loess. This paper introduces the definitions and calculation methods of structural stability coefficient, structural variability coefficient and stress comprehensive structure potential (stress-CSP) based on stress, and redefines the concept of over-consolidation ratio. We quantitatively evaluate the structural stability and consolidated state of Luochuan loess profile using these new concepts and methods.The results indicate that structural stability of Q4, Q3 new-loess is poor and at under-consolidated state. Correspondingly, structural stability of Q2 old loess is relatively good and at normal consolidated or slightly over-consolidated state. the research results above comply with loess microstructural properties and engineering practice.(3) With the concept of strain-CSP, we deduce the equations between structural parameter and collapsible coefficient, between water sensitivity and compression coefficient, and quantitatively analyze the variation rules of between structural parameter and water sensitivity parameter on Luochuan loess profile.According to the interaction theory of loess three-phase material, we put forward loess microstructure concept model, and establish general effective stress model of unsaturated soil. Under these models, we explain the mechanical mechanism of loess under-consolidated property and structural compression failure, and conclude the calculation method of structural loess consolidation settlement.(4) We deduce the calculation formula of structural strength and the relation between structural strength and shear strength by the means of the theory of shear strength. Through the triaxial shear test of original loess and remolded loess, we quantitatively analyze the variation rules of loess structural strength and shear strength when profile changes, and the relationships with the content of water.Following, we fit the relationship between the shear strength parameters (i.e. cohesion, internal friction angle) of original loess and remolded loess and the content of water, and discuss the approximate method to estimate original loess strength parameters by remolded loess shear strength parameters, which provide new way to solve the problems that there is great data dispersion and strength parameters variability in original loess triaxial shear test. Meanwhile, we analyze the mechanical mechanism of loess structural compressive failure, according to the p-q stress paths of triaxial shear test.(5) With the help of loess CT-triaxial shear test, we analyze the CT values, damage variable and the whole damage evolution of loess mesostructure during the initial process, consolidation and shear process, and eventually establish evolution equations of loess structural damage variable with scale effect on the basis of principle of damage mechanics. Also, we make a quantitative analysis on the mechanism of loess mesostructural damage and harden yield during the triaxial shear process, based on the CT images processing.更多还原