【作者】 马伯宁；

【导师】 谢新宇；

【作者基本信息】 浙江大学 ， 岩土工程， 2013， 博士

【摘要】 土体力学行为的研究通常有宏观尺度和微观尺度两条并行的研究主线。土体在宏观尺度上表现的力学行为归根结底是由其微观尺度的颗粒与结构的特性决定的。因此,宏观尺度与微观尺度相结合的研究,将微观的物理试验与力学分析用于解释土的宏观力学特性具有很强的理论价值与实际意义。现有的软粘土流变固结研究中较少涉及软土微观特性和形态对软土流变固结与变形的影响,然而软土的矿物组成和微观结构的性质对其流变固结有重要的影响。另外,当前关于流变固结过程中考虑土体自身应力历史的研究并不多见,理论分析中应当考虑流变固结过程中土压缩性与渗透性参数非线性变化的性质。本文正是遵循这一思路,针对软粘土的流变固结问题,分别在微观与宏观尺度上开展了试验与理论的研究,尝试为这一经典的土力学问题提出一些新的观点和思路。文中主要的工作如下：(1)对宁波滨海粘土开展GDS先进固结仪试验,分析研究该类型粘土的非线性压缩特性和再压缩特性,对常用的几种非线性压缩模型进行拟合分析,为非线性流变固结理论研究提供依据。对杭州粘土开展微观尺度试验,包括：①应用X射线能谱分析测定粘土的元素组成；②采用X射线衍射分析方法对粘土材料进行物相分析；③利用扫描电镜与压汞试验观测不同压力等级下经固结和流变后粘土的微观形貌特征,测定其孔隙分布规律及其变化,为微结构力学模型的建立提供依据。(2)在粘土微观形态和结构研究的基础上,提出能描述荷载作用下土体微观结构变形特性的物理模型。对模型进行力学分析,推导得到宏观力学参量与微观参数之间的关系,应用非线性突变理论建立软土的微结构力学模型和本构关系。模型中涉及土的孔隙分布、微结构变形特性、粘弹性应力应变关系等,并采用室内土工试验来验证其理论的正确性。(3)建立考虑软土应力历史的线性与非线性流变固结宏观唯象模型,在此基础上得到相应的流变固结控制方程,采用半解析方法对其进行求解。综合考量地基土体的应力历史、外部荷载、土的压缩性、流变性、渗透性、双层地基土体相对厚度等因素,对考虑应力历史条件下的单层和双层地基(带软弱下卧层)一维线性与非线性流变固结性状进行分析和研究。(4)基于Leonards和Bjerrum的研究,分析了土体的老化现象及其发生的机理。针对准先期固结应力和“消失”的先期固结应力两种典型的老化土体的力学现象,开展了对应的非线性流变固结问题理论研究工作。在四元件流变模型和实验数据拟合得到的参数模型的基础上给出了控制方程,利用半解析方法对其求解后分析土体老化对固结性状的影响。更多还原

【Abstract】 Research on macro scale and micro scale are two main streams of the studies on soil mechanics. It is known that soil behavior on macro scale ultimately depend on the characteristics of the soil particle and micro structure. Therefore, micro scale tests and analysis have scientific merit in terms of a fundamental assessment of its mechanism and associated parameters as well as practical implications in terms of explaining soil behavior. Present researches merely involve micro scale testing and analyzing in studies of rheological consolidation, but the mineral composition and micro structure have significant influence on consolidation behavior. Furthermore, rheological consolidation theory which takes soil stress history into account can be seldom found in literature. Bearing all these in mind, the author carried out theoretical and experimental research both on micro and macro scale on rheological consolidation of the soft soils, in order to advance the state-of-the-art with respect to our understanding of the mechanisms and significance of such a classic topic in soil mechanics. Main works are as below:(1) GDS one dimensional advanced consolidation testing system is used in soil laboratory tests to study the non-linearity in compression and recompression of Ningbo clay. Curve fit of the test data provides soil parameters of the non-linear compression models, which laid foundation for the non-linear rheological consolidation theory. Micro scale tests include X-ray EDS, XRD, SEM and MIP tests. X-ray EDS unveils the basic elements and their content in Hangzhou clay, XRD test demonstrates the main minerals in soil, SEM and MIP tests show micro morphological characteristics and pore size distributions of clayey soils after which are consolidated under different stresses.(2) A micro structural catastrophic model for soft soils is presented adopting phenomenological methods, which can describe the rheological consolidation behavior of soft clays. The model is verified by a series of rheological consolidation experiments with different loading rates. Creep deformation, which is loading rate dependent, can be clearly observed in these tests. Model parameters are gained by curve fit from test data. With only two free parameters, good fits of the data are achieved. The characteristics of the parameter demonstrate the feature of the micro-mechanical behavior of the clay.(3) The Gibson-Lo rheological model is used to simulate the coupled processes of drainage and creep of soft soils that takes stress history into account. A hybrid combination of analytical and numerical methods is adopted to solve the governing equations of consolidation with the nonlinear rheological model. The methodology is applied to a saturated soft soil subjected to surface loading. The soil profile is separated into normally consolidated and overconsolidated layers by a boundary that is allowed to move. Comparisons of the model predictions and its simulations are used to evaluate the effects of stress history, model parameters, and loading pattern on consolidation behavior. In non-linear analysis, variations in compressibility and permeability are captured using bi-linear e-logp and e-logkv models with the break in behavior controlled by the yield stress. The relative magnitude of the applied stress to the yield stress of clays is found to influence the rate of consolidation as well as the ultimate settlement. In addition, the ratios of the model parameters Cc/Ck, Ce/Cc and Cke/Ck are shown to have different effects on the consolidation behavior of clays.(4) The final section is on the increased yield stress of clays due to time effects termed the quasi-preconsolidation pressure. A nonlinear rheological model for clays incorporated into the governing equation is used to numerically simulate the consolidation process of clay in laboratory tests to identify the basic mechanical parameters that contribute to the development of the quasi-preconsolidation phenomenon. A change in modulus in the recompression region due to ageing is shown to be the dominant cause of the development of the quasi-pc phenomenon. While the soil modulus variation controls the EOP curve of clays, observed time effects such as the "vanishing pc" phenomenon are controlled primarily by changes in soil viscosity. This has no bearing on the development of the quasi-pc phenomenon.更多还原