【作者】 王梅；

【导师】 白晓红；

【作者基本信息】 太原理工大学 ， 岩土工程， 2010， 博士

【摘要】 从土的结构性出发进行土的工程性质的研究已成为土力学发展的新方向,而黄土由于其特殊的结构所具有的湿陷性为黄土地区的建设安全带来了巨大的隐患。湿陷性黄土在天然状态下可以保持较高的强度和较低的压缩性,但遇水浸湿后,结构迅速破坏,发生突然的下沉变形,强度也随之大幅下降,具有极大的危害性。本文依托国家自然科学基金项目“中国黄土的微观结构与湿陷性”(项目编号:50478096),通过选取我国不同黄土地区的典型湿陷性黄土土样,结合大量的室内土工试验,并借助扫描电子显微镜测试技术,对黄土的微结构图像进行了细致的定性分析以及定量评价,从黄土的结构特性出发,对黄土的湿陷机理及湿陷变形规律进行综合研究,提出了造成黄土湿陷的主要结构因素,总结了微结构特征与湿陷性之间的统计关系,为正确评价黄土的湿陷性并有效控制黄土的湿陷变形提供了理论依据,对我国黄土地区的工程建设事业的发展具有积极的意义。主要研究成果归纳如下:1)通过黄土的颗粒分析试验得出,黄土的颗粒组成以粗粉粒为主,也含有较多的黏粒。土体中黏粒含量的增多在一定程度上会降低黄土的湿陷性,但不能仅根据黏粒的含量来判断黄土的湿陷性。一些地区的土样黏粒含量在30%以上,仍具有较强烈的湿陷性。利用扫描电镜对该土体结构进行观察,发现其原因为黏粒只是存在于团粒的内部,而团粒表面起骨架胶结作用的黏粒很少,团粒之间呈松散排列,土体存在较大的湿陷性,黏粒的高含量对于黄土的湿陷性没有影响。所以考虑黏粒对黄土湿陷性的影响,除考虑其含量外,还要重点确定其在土体中的赋存状态。2)通过反复试验,成功研制出一套适合于湿陷性黄土微观结构分析的制样方法,并确定了适用于黄土浸泡的液体材料及配比,在不扰动土体结构的前提下,获得清晰的微观图像,为今后湿陷性黄土的结构研究奠定了基础。3)在前人对黄土结构总结的基础上,对黄土的结构进行了更合理的分类。将黄土的基本单元体形式归纳为颗粒状单元体、团粒状单元体;单元体间的连结方式划分为接触连结和胶结连结;根据单元体不同的排列方式而形成的孔隙分为单元体内孔隙、镶嵌孔隙、架空孔隙、大孔隙。4)根据孔径的大小将孔隙划分为大孔隙(>500μm)、中孔隙(500-50μm)、小孔隙(50-5μm)和微孔隙(<5μm),并将其与根据单元体的排列形式划分的孔隙类型相对应。单元体内孔隙基本属于微孔隙,镶嵌孔隙与小孔隙相对应,架空孔隙包括中孔隙和孔壁未加固的大孔隙。将各种结构的孔隙形式具体量化,便于今后对孔隙结构进行定量分析。5)通过对不同地区黄土微结构的分析总结,并与其湿陷性相对比,得出在黄土结构特征的三个基本要素中,以单元体间的排列方式最为重要。骨架单元体之间松散排列形成的架空孔隙是黄土产生湿陷的根本原因。6)根据土样的扫描电镜微观图像为二维图像的特点,确定将孔隙面积比作为微结构定量分析的主要测量参数。对于IPP图像处理软件得出的数据进行了全面的分析和研究,最终确定以放大倍数1000倍,以灰度分布曲线上后方峰值的左侧坡脚(峰值左侧)所对应的阈值,来统计土样的孔隙面积比。7)按照确定的放大倍数和阈值取值方法统计出各地土样的孔隙面积比,并与室内土工试验得出的孔隙率相对比进行验证,得出所确定的微结构分析方法合理,统计数据对于土体的微结构特征具有一定的代表性。8)根据土样的微结构图像定量分析结果,土样垂直面的结构规律性要好于水平面,垂直面的孔隙面积比随埋深的增加而减小,其变化呈线性关系;湿陷系数随孔隙面积比的增加而增大,孔隙面积比与湿陷系数之间呈对数曲线关系。总结得出了黄土孔隙面积比与埋深之间的线性回归方程式,以及孔隙面积比与湿陷系数间的对数回归方程式。9)通过黄土的各项物理性质与湿陷性的关系研究得出,随着含水量、重度、干重度、饱和度的增加,黄土的湿陷系数降低,湿陷性减弱;随着孔隙比、孔隙率的增加,黄土的湿陷系数提高,湿陷性增强。并分析总结了非湿陷性黄土和强湿陷性黄土所对应的各项物理性质指标,对工程实践中正确评价黄土湿陷性具有一定的指导意义。10)通过黄土的不同初始含水量固结试验得出,随着初始含水量以及初始饱和度的增加,土样的压缩变形增大,湿陷系数减小,黄土的湿陷性降低。更多还原

【Abstract】 The study on engineering properties of soil based on its structure has been a new direction in the development of soil mechanics. The collappsibility of loess caused by its special structure brings on the tremendous risks in the large number of constructions on the collapsible loess foundation. Collapsible loess in natural state has relatively high strength and low compressibility, but when it is soaked with the water, its structure will be damaged rapidly and collapsed suddenly, at the same time its strength losts a lot, so collapsibility has great harmfulness. Under the support of project“Microstructure and collapsibility of loess in China”funded by National Nature Science Foundation (Project No. 50478096), this study is conducted and completed. In this study, typical collapsible loess samples were taken from different loess regions in China. After a series of tests to determine their physical and mechanical properties, the samples were observed under the scanning electric microscope. The images of loess were analyzed from both qualitative and quantitative ways. Based on the structural properties, the collapse mechanism and the law of deformation were studied, the main structural factors causing loess collapse were suggested, and the relationship between collapsibility coefficients and microstructure properties of loess specimens were concluded. There is an important positive meaning to provide the theoretical basis for evaluating the loess collapsibility correctly and controlling the loess deformation effectively.The main achievements in this study are as follow:1) According to the grain size distribution tests, the content of coarse silt particle is the largest portion in loess specimens, and the content of clay particle is rather high in general. To a certain extent, the content of clay particle increasing can decrease the collapsibility of loess. But it is impossible to judge the collapsibilty based only on the content of clay particle. Though the contents of clay particle in some specimens are more than 30%, they still have strong collapsibility. Using scanning electron microscope to observe the structure of these specimens and found that the most of clay particles existed inside the aggregates, while little clay particle existed among the aggregates to cement them, the aggregates were in loose arrangement and the specimens had the high collapsibility. The high content of clay particle doesn’t make a difference on the collapsibility of loess. So to determine the effect of clay particle on the loess collapsibility must consider not only the content of clay particle, but also the clay particle exsiting state in the loess, later one maybe of more importance.2) A set of sampling method for collapsibility loess microstructure analysis, the materials for specimen impregnation and their ratio were determined after lots of repeated tests. By this method, large numbers of clear undisturbed microstructural images were obtained what provided the foundation of the loess structure research.3) A reasonable classification of loess structure was proposed based on the former research of loess. The basic unit element in loess microstructure composite can be summed up as granular unit and aggregated unit; the link between the basic unit elements can be classified as contact link and cement link; the arrangement of basic unit elements leading to various void in loess can be divided into 4 types, ie, void inside the unit, embedded void, open void and large void.4) The voids in loess can be divided into large void (>500μm), middle void (500-50μm), small void (50-5μm) and micro void (<5μm) at their size. This classification is associated with the void form divided by the arrangement of basic unit element. Most of voids inside the unit are mico voids; the embedded voids correspond to the small voids; the open voids include middle voids and large voids with loose void wall. It is possible to quantitatively analyze the void with different structure based on their specific size range.5) Contrasting the analysis result of loess structure in different regions to their collapsibility, the conclusion can be drawn that the arrangement of basic unit elements is the most important part in three structural characters. The open void formed by loose arrangement of basic unit elements is the primary cause of loess collapsibility.6) The void area ratio of specimen was decided to be the main measurement parameter in the structure quantitative analysis of loess on the basis of the SEM image’s feature of two-dimension. Based on the analysis of data got from IPP image processing software, the method of calculating the void area ratio was determined. The void area ratio of each specimen can be calculated by choosing the image with the magnification of 1000 and selecting the gray scale threshold as the value corresponding to the left foot of the rear peak on the gray distribution curve.7) The void aera ratio of specimens in different regions calculated by the method mentioned above was verified by contrasting with the porosity of specimens resulted from the soil tests in laboratory. It is certified that the method of calculating void area ratio is reasonable, and the statistical data has the great representation for the structure of loess.8) The quantitative analysis results of specimen image show that the regularity of vertical plane structure of specimen is better than horizontal plane. The void area ratio of vertical plane decreases with the sample depth increases, and increases with the collapsibility coefficient increases. The relationship equations are set up, such as the linear regression equation of void area ratio and depth, the logarithm regression equation of void ratio and collapsibility coefficient.9) By the study on the relationship between physical properties and collapsibility of loess, the conclusion can be drawn as follow: with the increasing of water content, unit weight, dry unit weight and saturation degree, the collapsibility coefficient of specimen reduces, the loess collapsibility declines; with the increasing of void ratio and porosity, the collapsibility coefficient of specimen increases, the loess collapsibility enhance. Besides, some physical property indexes are compared and discussed for non-collapsible loess and strong collapsible loess are concluded. The work is significant for evaluating the loess collapsible correctly.10) From the consolidation tests of loess with different initial water content, the conclusion can be drawn that with the initial water content and the initial saturation degree increase, the compression of specimen increases, while the collapsibility coefficient decreases, the collapsibility of loess decreases.更多还原