基于双尺度的软土流变固结理论与试验研究

发布时间：2018-06-02 01:46

本文选题：软土 + 双尺度　；参考：《浙江大学》2013年博士论文

【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。
[Abstract]:The study of soil mechanical behavior usually has two parallel main lines: macro scale and micro scale. The mechanical behavior of soil on macroscopic scale is determined by the characteristics of particle and structure in microscopic scale. Therefore, it is of great theoretical value and practical significance to apply the microscopic physical test and mechanical analysis to explain the macroscopic mechanical properties of soil in the study of macro scale and micro scale. In the present study of rheological consolidation of soft clay, the influence of microcosmic characteristics and morphology of soft clay on rheological consolidation and deformation of soft clay is seldom discussed. However, the mineral composition and microstructure of soft clay have an important effect on rheological consolidation of soft clay. In addition, there are few researches on the stress history of soil in rheological consolidation process, and the nonlinear variation of soil compressibility and permeability parameters should be considered in theoretical analysis. In this paper, the rheological consolidation of soft clay has been studied on the micro scale and macroscopic scale, and some new ideas and ideas have been put forward for this classical soil mechanics problem. The main work in this paper is as follows: In this paper, the GDS advanced consolidation instrument test is carried out on Ningbo coastal clay. The nonlinear compression characteristics and recompression characteristics of this type of clay are analyzed, and several commonly used nonlinear compression models are fitted and analyzed. It provides a basis for the study of nonlinear rheological consolidation theory. The microscale tests were carried out on the clay in Hangzhou, including the determination of the element composition of the clay by X-ray energy spectrum analysis. The phase analysis of the clay material was carried out by means of X-ray diffraction analysis. (3) scanning electron microscopy (SEM) and mercury injection test were used to observe the microstructure of clay after consolidation and rheology under different pressure levels, and the pore distribution and its changes were measured, which provided the basis for the establishment of microstructural mechanics model. 2) based on the study of the microstructure and structure of clay, a physical model which can describe the deformation characteristics of soil microstructure under load is proposed. The relationship between macroscopic and microscopic parameters is derived by mechanical analysis of the model, and the microstructural mechanics model and constitutive relation of soft soil are established by using nonlinear catastrophe theory. The pore distribution of soil, deformation characteristics of microstructure, viscoelastic stress-strain relationship and so on are involved in the model. Laboratory geotechnical tests are used to verify the correctness of the theory. 3) the macroscopic phenomenological model of linear and nonlinear rheological consolidation considering the stress history of soft soil is established, and the corresponding rheological consolidation control equation is obtained, and the semi-analytical method is used to solve it. The factors such as stress history, external load, compressibility, rheology, permeability, relative thickness of soil on double-layer foundation are comprehensively considered. The one-dimensional linear and nonlinear rheological consolidation behavior of single-layer and double-layer subgrade (with weak underlying layer) under the condition of stress history is analyzed and studied. (4) based on the research of Leonards and Bjerrum, the aging phenomenon of soil and its occurrence mechanism are analyzed. Aiming at the mechanical phenomena of two typical aging soils, the quasi-pre-consolidation stress and the "vanishing" pre-consolidation stress, the corresponding theoretical research on the nonlinear rheological consolidation problem was carried out. On the basis of the four-element rheological model and the parameter model fitted from the experimental data, the governing equation is given. The effect of soil aging on the consolidation behavior is analyzed by semi-analytical method.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU447

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