软土孔隙结构特征与渗流特性试验研究

发布时间：2018-06-01 06:08

  本文选题：软土 + 渗流特性　； 参考：《华南理工大学》2014年博士论文

【摘要】：软土广泛分布于沿海、河流中下游及湖泊的三角洲地区,一般具有高含水量、大孔隙、低强度、高压缩性、低渗透性、结构性和流变性等特点,其工程力学性状复杂且工程性质差,软土的渗透固结特性是土工建设工程中不可回避的问题之一。土的力学性质从本质上来说是取决于其微结构,土的微孔隙特征是研究土体微结构的重要内容,土体孔隙的结构形态特征与土的渗透固结特性关系密不可分。本文基于试验从微观的角度研究了软土的孔隙结构特征及其与渗透固结特性的关系。本文研究的对象包括极细颗粒人工土和珠江三角洲地区的软土。采用的宏观试验方法有固结渗透试验、常水头渗透试验和变水头渗透试验,微观试验方法以压汞试验(MIP)为主、还包括扫描电镜试验(SEM)、X射线衍射(LD)、激光衍射法试验(XRD)、气体吸附法(BET)、乙二醇乙醚吸附法(EGME)等。本文开展的研究工作和取得的成果有如下几个方面:(1)研究了土体微观试验脱水过程中冷冻干燥法、烘干法和风干法对软土孔隙结构的影响,为微观试验分析奠定了基础。对于含水率大、高塑性的天然软土应使用冷冻干燥法干燥。(2)试验验证了用压汞试验获得软土比表面积的可行性与可靠性,因此可以在获得土体孔隙分布特征的同时获得土体的比表面积,简化了试验。(3)定量研究了软土固结渗透过程中孔隙分布结构的变化,发现在软土固结渗透过程中孔隙直径小于100nm的小孔隙含量与分布不变规律,渗透固结改变的主要是孔隙直径在100nm和10000nm之间的中孔隙含量和分布,并从微观孔隙的角度对这一现象进行了机理分析与探讨;(4)用压汞试验测试分析了大量不同成分、孔隙比、含水率、饱和度的人工软土以及珠江三角洲天然软土孔隙分布特征。压汞试验结果表明软土孔隙特征的多样性,因此工程中采用的表达土的孔隙含量的宏观参数孔隙比并不能完整描述软土的孔隙特征,需要引入其他微观参数对软土的孔隙特征进行描述。(5)统计分析了人工土和天然软土的孔隙结构特征参数和渗透系数的关系。根据试验结果和理论分析把土中孔隙分类为小孔隙(D≤100nm)、中孔隙(100nmD≤10000nm)和大孔隙(D10000nm)。统计分析表明,渗透系数与压汞孔隙比、中孔隙体积绝对含量没有相关性或弱相关,与小孔隙体积绝对含量呈现中等相关,与比表面积呈现中等相关或强相关,与平均孔径和大孔隙体积绝对含量强相关。(6)从微观孔隙结构的角度探讨了渗透固结的机理,提出小孔隙孔隙比、中孔隙孔隙比、大孔隙孔隙比和有效孔隙比概念与假设。基于K-C模型,根据有效孔隙比假设重新推导了考虑微观孔隙特征的修正的K-C模型。经过试验验证,相对于传统的K-C模型,修正的K-C模型更加适合珠江三角洲地区软土。
[Abstract]:Soft soil is widely distributed in coastal, middle and lower reaches of rivers and deltas of lakes. It is generally characterized by high water content, large porosity, low strength, high compressibility, low permeability, structural and rheological properties, etc. The engineering mechanical properties are complex and the engineering properties are poor. The permeability and consolidation of soft soil is one of the unavoidable problems in geotechnical engineering. The mechanical properties of soil are essentially determined by its microstructure. The characteristics of soil micropores are an important part of the study of soil microstructures. The structural and morphological characteristics of soil pores are closely related to the permeability and consolidation characteristics of soil. Based on the experiments, the pore structure characteristics of soft soil and its relationship with permeability and consolidation characteristics are studied from the microscopic point of view. The objects of study in this paper include very fine grained artificial soil and soft soil in the Pearl River Delta region. The macroscopical test methods are consolidation permeation test, constant head permeation test and variable head permeation test, and the microcosmic test methods are mercury injection test (MIP). It also includes scanning electron microscopy (SEM), X-ray diffraction (LDN), laser diffraction (XRDX), gas adsorption (et), ethylene glycol (EG) adsorption, and so on. The research work and the results obtained in this paper are as follows: 1) the effects of freeze-drying, drying and air-drying on the pore structure of soft soil are studied in the process of soil micro-test dehydration, which lays a foundation for micro-test analysis. For the natural soft soil with high moisture content and high plasticity, the freeze-drying method should be used to dry. 2) the feasibility and reliability of using mercury injection test to obtain the specific surface area of soft soil are verified. Therefore, the pore distribution characteristics of soil can be obtained, and the specific surface area of soil can be obtained, and the change of pore distribution structure during consolidation and permeation of soft soil can be quantitatively studied by simplified test. It is found that in the process of consolidation and permeability of soft soil, the pore content and distribution of the pore diameter is smaller than that of 100nm, and the change of pore diameter between 100nm and 10000nm is the main change of pore content and distribution. The mechanism of this phenomenon is analyzed and discussed from the point of view of micro-porosity. The pore distribution characteristics of a large number of artificial soft soil with different components, void ratio, water content, saturation and natural soft soil in the Pearl River Delta are analyzed by mercury injection test. The results of mercury injection test show that the diversity of pore characteristics of soft soil, so the macro parameter porosity ratio, which is used to express the pore content of soft soil, can not describe the pore characteristics of soft soil completely. The relationship between pore structure characteristic parameters and permeability coefficient of artificial soil and natural soft soil is analyzed statistically. According to the experimental results and theoretical analysis, the pores in the soil are classified as small porosity D 鈮，

本文编号：1963126