珠江三角洲软土显微结构与渗流固结机理研究

发布时间：2018-07-10 18:35

本文选题：珠江三角洲软土 + 渗流固结特性　；参考：《华南理工大学》2013年博士论文

【摘要】：珠江三角洲地区广泛分布着厚度几米至几十米的全新世海积形成的软土层，主要为淤泥、粉砂质淤泥和黏土，具有含水量高、孔隙比大、压缩性高、强度低、渗透性差、结构性和流变性显著等特点而导致地基沉陷和失稳等重大工程事故。为提高软土地基的工程质量，减少工程施工事故，需要深入研究软土的工程特性，提高软土地基的设计和施工水平。但长期以来，人们主要从宏观层次对软土的工程特性进行研究，难于抓住决定软土性质的本质因素从而对其工程特性作出深刻研究。因此，从土体的微观结构分析入手研究软土工程性质是一种“寻根溯源”的方法，可以从本质上深刻了解软土的工程特性。本文以珠江三角洲天然土(或重塑土)为研究对象，从统计学角度研究珠江三角洲软土区域特征及工程性质，并结合矿物成分试验、ESEM试验、压汞试验研究软土渗流固结过程中微观结构因素(如颗粒形状、分布、排列和连结方式、微颗粒聚合体的形态、孔隙数量、孔隙形态、尺度及分布、连通性及曲折性等)的变化特征与分形特征，将软土的微观参数与宏观工程性质结合，解释影响软土特性的微观机制。最后，提出了基于微观试验的修正固结模型，通过实测结果证实了模型的合理性和有效性。本文得到的主要研究成果和结论如下： (1)通过对珠江三角洲软土成因的地质与水文环境、矿物成分、颗粒特征、微观特征等区域特性分析，发现其特殊的宏观工程特性主要由微细观因素决定。利用“偏度、峰度检验法”研究了珠江三角洲软土物理力学指标的分布规律，为今后该地区开展软土工程提供借鉴。 (2)与全局阈值分割法相比，局部阈值分割法得到的孔隙比结果与实际更接近。将显微结构二值化定量分析的阀值选择与微孔隙特征测试、三相图计算相匹配的方法，解决目前微观试验结果定量分析中的过渡离散性和人为干扰问题，改善现有微观试验的可靠性和准确性。 (3)固结过程中，软土微结构类型逐步发生变化，由蜂窝结构(海绵结构)逐渐向骨架结构、紊流结构、密实结构转化，其连接方式由边-边，边-面连接向面-面连接转化，结构单元体面积明显增加，孔隙减小；重塑土颗粒由于缺乏结构性，揉合在一起，以聚合体为主，呈凝块状结构，相对密实，随着荷载的增加，颗粒单元体以面-面连接方式为主。 (4)结构单元体及孔隙的微观结构定量化参数在固结的不同阶段具有不同的规律。在固结前期，当有效应力较小时，由于淤泥土具有一定的结构强度，微观结构处于稳定调整阶段，孔隙数量较少，孔隙比较大，以大、中孔隙为主，结构单元体和孔隙的大小、形态和定向性等变化幅度均较小；当有效应力增至结构屈服应力时，结构逐渐破坏，团聚体破碎，微观结构处于再造剧烈调整阶段，结构单元体等效直径明显增大，，圆形度和平均形状系数显著减小，有变狭长趋势并在垂直于压力方向形成明显的定向排列。此时，孔隙数量明显增加，等效孔径不断变小，形态变得更为复杂，孔隙分布由中、小孔隙向小、微孔隙甚至超微孔隙发展，但定向性变化不明显；当有效应力继续增大时，新的微观结构作适当调整，结构单元体与孔隙的定量化参数变化多趋于平缓。 (5)珠江三角洲天然软土(或重塑土)的结构单元体和孔隙均具有明显的分形结构特征。综合反映孔隙大小、形态、分布、定向性四方面特征的孔隙结构影响因子与荷载之间具有良好的相关性。研究表明，软土的宏观工程性质与微观参数之间存在紧密联系，固结土的压缩性、渗透性均可由天然部分和固结变化部分构成。其中，天然部分与初始结构性特征(主要是孔隙特征)相关，一般同时与多个结构参数相关；而固结变化部分与固结引起的结构性特征(主要是孔隙特征)的变化相关，最终可表达为与固结压力的关系。 (6)建立基于微细观试验(经验公式)的修正固结模型，通过实测结果证实了模型的合理性和有效性。修正固结模型基于土体微细观结构特别是微细孔隙结构特征的物理机制，反映土体固结与荷载的非线性关系。
[Abstract]:The Pearl River Delta region is widely distributed in the soft soil layers formed by the Holocene sea of a few meters to dozens of meters, mainly silt, silt silt and clay, with high water content, large pore ratio, high compressibility, low strength, poor permeability, and significant structural and rheological properties, which lead to ground subsidence and instability. In order to improve the quality of the soft soil foundation and reduce the construction accidents, it is necessary to study the engineering characteristics of soft soil and improve the design and construction level of soft soil foundation. However, for a long time, people mainly study the engineering characteristics of soft soil from the macro level, so it is difficult to grasp the essential factors determining the soft soil properties so as to make the engineering characteristics of the soft soil. Therefore, it is a kind of "root search and traceability" method to study the engineering properties of soft soil from the analysis of soil microstructure, which can deeply understand the engineering characteristics of soft soil in essence.
In this paper, the natural soil (or remolded soil) in the Pearl River Delta is taken as the research object. The characteristics and engineering properties of the soft soil in the Pearl River Delta are studied from a statistical point of view. The microstructure factors (such as particle shape, distribution, arrangement and connection mode, micro particle polymerization) in the process of seepage consolidation in soft soil are studied with mineral composition test, ESEM test and mercury injection test. The change characteristics and fractal characteristics of body shape, pore number, pore shape, scale and distribution, connectedness and zigzag, combine the micro parameters of soft soil with the macroscopic engineering properties, and explain the micro mechanism affecting the soft soil properties. Finally, a modified consolidation model based on the microscopic test is proposed, which confirms the combination of the model through the measured results. Rationality and effectiveness.
The main findings and conclusions obtained in this paper are as follows:
(1) through the analysis of the geological and hydrological environment, mineral composition, particle characteristics and microscopic characteristics of the soft soil in the Pearl River Delta, it is found that the special macroscopic engineering characteristics are mainly determined by the microcosmic factors. The distribution of the physical and mechanical indexes of the soft soil in the Pearl River delta is studied by using the "skewness and kurtosis test". The soft soil engineering in this area can be used for reference.
(2) compared with the global threshold segmentation method, the porosity ratio obtained by the local threshold segmentation method is closer to the actual results. The method of matching the threshold selection of the two value quantitative analysis of the microscopic structure with the micropore gap characteristics and the three-phase diagram calculation can solve the problem of the transition dispersion and the human interference in the quantitative analysis of the present microscopic test results. The reliability and accuracy of the existing microtest.
(3) during the consolidation process, the type of the soft soil microstructure gradually changes, and the honeycomb structure (sponge structure) is gradually transformed into the skeleton structure, the turbulence structure and the dense structure, and the connection mode is transformed from side to side, side to surface connection to surface to surface, the area of the structure unit increases obviously and the pore decreases, and the remolded soil particles are knead due to lack of structure. Together, the polymer is mainly clot structure and relatively dense. With the increase of load, the particle element is mainly composed of surface to surface connection.
(4) the quantitative parameters of structural unit and pore microstructure have different regularities at different stages of consolidation. In the early consolidation period, when the effective stress is small, the microstructure is in the stable adjustment stage because the mud soil has a certain structural strength, the number of pores is less, the pore is larger, the main pore is the main pore, and the structure unit is the main body. When the effective stress increases to the structural yield stress, when the effective stress increases to the structural yield stress, the structure gradually destroys, the aggregate is broken, the microstructure is in the stage of drastic adjustment, the equivalent diameter of the structural unit increases obviously, the circle degree and the mean shape coefficient decrease significantly, and have a trend of changing and perpendicular to the vertical. In the direction of pressure, there is a clear directional arrangement in the direction of pressure. At this time, the number of pores increases obviously, the equivalent pore size becomes smaller and the shape becomes more complex. The pore distribution is from medium, small pore to small, micropore and even ultramicro pore, but the directional change is not obvious. When the effective stress continues to increase, the new microstructure is properly adjusted, structure single The variation of quantitative parameters of the element and pore tends to be gentle.
(5) the structural elements and pores of the natural soft soil (or remolded soil) in the Pearl River Delta have obvious fractal structure characteristics. The influence factors of pore structure, which reflect the four aspects of pore size, morphology, distribution and orientation, have good correlation with the load. The research shows that the macroscopic engineering properties of soft soil and the micro parameters are between the parameters. The compressibility of the consolidated soil, the compressibility of the consolidated soil, and the permeability can be made up of the natural and consolidation parts. The natural part is related to the initial structural characteristics (mainly pore characteristics), generally related to the structural parameters, and the structural characteristics (mainly pore characteristics) caused by the consolidation change part and the solid junction. Chemical correlation can eventually be expressed as the relationship between consolidation pressure.
(6) to establish a modified consolidation model based on the micro observation test (empirical formula), and verify the rationality and effectiveness of the model through the measured results. The modified consolidation model is based on the physical mechanism of the micropore structure, especially the characteristics of the micro pore structure, reflecting the nonlinear relationship between the consolidation and load of the soil.
【学位授予单位】：华南理工大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU447

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