宣城网纹红土结构性的微观定量研究

发布时间：2018-08-13 17:09

【摘要】：原状网纹红土同重塑网纹红土的宏观力学特性存在差异,而土体宏观力学特性由其微观结构决定。为从微观角度深入揭示原状和重塑网纹红土力学特性差异,本文基于室内击实试验和SEM-EDS试验及数字图像处理技术,以对他们的微结构进行定量对比分析,分析了不同放大倍数和不同阈值选取对有效阈值区间内三维孔隙率计算结果的影响,并探讨了平均接触面积率与宏观孔隙率之间的关系。通过研究得出如下主要结论:(1)基于重塑网纹红土SEM试验结果和数字图像处理技术,构建了以像素面积为底面、阈值范围为高度的有效阈值区间内三维孔隙率计算模型,并实际应用于不同试验条件下的SEM图像孔隙数量、面积及孔隙率演变分析,与平面孔隙率方法结果对比表明三维孔隙率计算结果更符合土体孔隙实际分布情况。(2)重塑网纹红土微观孔隙率定量结果表明,由SEM图像计算获得的三维孔隙率大都大于宏观孔隙率,2000倍下SEM计算结果更接近宏观孔隙率,同时发现阈值选取是定量分析的关键点,基于平均阈值获得的三维孔隙率结果偏差比选取最终阈值获得的结果要小得多。平均接触面积率分析表明,试样计算所得平均接触面积率大概在3%以下,并结合网纹红土粘土矿物结合水膜厚度300?特点,拟合得到平均接触面积率与宏观孔隙率之间的幂函数关系。(3)原状网纹红土微结构研究结果表明,红色基质中土颗粒排列紧密,孔隙率较小且孔隙之间的连通性较差,土颗粒表面比较粗糙;白色网纹中孔隙率大且孔隙数量多,颗粒多表现为光滑的片状结构,主要以面面接触为主。定量分析结果表明红色基质的计算三维孔隙率均值为0.371,白色网纹的计算三维孔隙率均值为0.450。(4)EDS试验分析结果表明红色基质和白色网纹中的主要化学元素为氧、硅、铝和碳,及少量的钾和镁。其中铁元素流失是造成白色网纹和红色基质色彩差别的主要原因,且铁元素有富集现象。碳元素为网纹红土中因有机酸形成酸性还原环境导致铁元素的迁移的观点提供了一定依据。
[Abstract]:The macroscopic mechanical properties of undisturbed reticulated red soil are different from those of remolded reticulated red soil, but the macroscopic mechanical properties of soil are determined by its microstructure. In order to reveal the difference of mechanical properties between the original and reconstructed reticulated red soil from the microscopic angle, this paper makes a quantitative comparative analysis of their microstructure based on the laboratory compaction test, SEM-EDS test and digital image processing technology. The influence of different magnification and different threshold on the calculation results of 3D porosity in the effective threshold range is analyzed, and the relationship between the average contact area rate and the macroscopic porosity is discussed. The main conclusions are as follows: (1) based on the SEM test results of remolded reticulated laterite and digital image processing technology, a three-dimensional porosity calculation model with pixel area as the bottom and threshold range as the height is constructed. And it is applied to analyze the evolution of porosity, area and porosity in SEM images under different experimental conditions. The comparison of the results with the plane porosity method shows that the three-dimensional porosity calculation results are more in line with the actual distribution of soil porosity. (2) the quantitative results of microscopic porosity of remolded reticulated red soil show that, The 3D porosity calculated by SEM image is mostly larger than that of macro porosity by 2000 times. The results of SEM calculation are closer to macroscopic porosity. At the same time, it is found that the selection of threshold is the key point of quantitative analysis. The deviation of 3D porosity based on the average threshold is much smaller than that obtained by selecting the final threshold. The analysis of average contact area ratio shows that the average contact area rate calculated by the sample is about 3%, and the thickness of water film is 300? The power function relationship between average contact area ratio and macroscopic porosity was obtained by fitting. (3) the results of microstructural study of undisturbed reticulated laterite show that the soil particles in red matrix are closely arranged, the porosity is small and the connectivity between pores is poor. The surface of soil particles is rough, the porosity of white mesh is large and the number of pores is large, and most of the particles are smooth flake structure, mainly surface contact. The results of quantitative analysis show that the calculated three-dimensional porosity of red matrix is 0.371, and that of white mesh is 0.450. (4) the results of EDS test show that the main chemical elements in red matrix and white mesh are oxygen, silicon, aluminum and carbon. And a small amount of potassium and magnesium. The loss of iron is the main reason for the color difference between white mesh and red matrix. The carbon element provides a certain basis for the viewpoint that the organic acid forms an acid reduction environment in the reticulated red soil, which leads to the migration of iron elements.
【学位授予单位】：合肥工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU446

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