黏性土的微观孔隙结构试验研究

发布时间：2018-04-19 02:28

本文选题：核磁共振 + 横向弛豫时间　；参考：《湖北工业大学》2013年硕士论文

【摘要】：土是一种物理性质非常复杂，而又与工程密不可分的地质材料。众所周知，土的物理力学性质是通过其微观结构起作用，因此展开对土微观结构的研究，岩土力学行为便可以从本质上得到解释。但是，鉴于土种类的繁杂多样化，其物理性质也各不相同，所需研究的物理参数也极其复杂，并且目前的测定技术有限，结果往往不可靠，以至于至今对土的研究还没有达到工程实用的要求；其次，由于软黏土上述的各种复杂情况，使得研究者们在对土体微观孔隙结构的定量分析研究，揭示软黏土的微观孔隙分布及其变化规律等，非常困难。由于这些实际困难，在以往的研究中，研究者们大多从宏观角度去研究土体的工程物理力学性质，从表象上去解释土的工程现象，但是这样不能揭示出引起这种工程现象的内在本质机理。武汉地区地基土质常常有着含水率高，压缩性大，孔隙率高等特点。本文所研究土为武汉市汉街地区一建筑工地基底软黏土，主要是由孔隙水，孔隙中气体，黏土颗粒等物质组成。本文通过大量的试验，定量化分析其孔隙孔径分布特征，以及在干密度变化的过程中，孔径分布的变化规律，为确定工程土体干密度对孔隙率、渗透性等的影响提供依据。本文所进行的主要研究工作以及获得的结论如下：（1）介绍了对土体结构性以及其微观世界的研究现状，指出以往所用试验方法所带来的一些不准确性，在本文中采用了更为先进，试验结果更为可靠的研究方法——核磁共振，并将其与常规研究方法压汞试验结果进行对比。（2）对所取试样土进行风干重塑，制成七种不同干密度试样，分别为：1.3g/cm3到1.705g/cm3之间，，并将试样抽真空饱和。（3）由核磁共振试验及CPMG反演软件得出各试样的核磁共振横向弛豫时间的分布曲线图，通过分析知横向弛豫时间与孔径成正比关系，换言之，该曲线图就反映着试样土的微观孔隙分布，发现T2在1.5~1.7ms时，孔隙分布最多。（4）由常规压汞试验法测出其孔径分布，得出干密度越大，试样的主要孔隙分布区域孔径越小，并由两种试验进行对比发现，干密度主要影响的是大孔隙的含量，对小孔隙含量改变不大；试验结果还表明该试样土的孔隙主要是大孔隙，均占到80%以上。
[Abstract]:Soil is a kind of geological material which has very complex physical properties and is closely related to engineering.It is well known that the physical and mechanical properties of soil play an important role through its microstructure. Therefore, the mechanical behavior of rock and soil can be explained in essence by studying the microstructure of soil.However, in view of the diverse variety of soil types, their different physical properties, the extremely complex physical parameters to be studied, and the limited existing techniques for determination, the results are often unreliable,So far, the research on soil has not reached the practical requirements of engineering. Secondly, due to the various complex situations mentioned above, researchers are making quantitative analysis of the micro-pore structure of soil.It is very difficult to reveal the micro-pore distribution and its variation law of soft clay.As a result of these practical difficulties, in previous studies, researchers have mostly studied the engineering physical and mechanical properties of soil from a macro perspective, and interpreted the engineering phenomena of soil from a superficial perspective.But this does not reveal the intrinsic mechanism that causes this kind of engineering phenomenon.The foundation soil in Wuhan area is often characterized by high moisture content, high compressibility and high porosity.The soil studied in this paper is a soft clay on the basement of a construction site in Hanjie area of Wuhan City, which is mainly composed of pore water, gas in pores, clay particles and so on.Through a large number of experiments, the characteristics of pore pore size distribution and the variation law of pore size distribution in the course of dry density change are analyzed quantitatively, which provides the basis for determining the influence of dry density on porosity and permeability of engineering soil.The main research work and conclusions obtained in this paper are as follows:1) this paper introduces the present research situation of soil structure and its microcosm, and points out some inaccuracies brought about by the test methods used in the past. In this paper, a more advanced and more reliable research method, nuclear magnetic resonance (NMR), is adopted.The results of mercury injection test were compared with those of conventional research methods.2) the sample soil was remolded by air drying, and seven kinds of samples with different dry densities were made, which ranged from: 1.3 g / cm ~ 3 to 1.705g/cm3, and the samples were saturated by vacuum.(3) the distribution curves of transverse relaxation time of nuclear magnetic resonance (NMR) were obtained from NMR test and CPMG inversion software. The relationship between transverse relaxation time and pore size was found to be in direct proportion by analysis, in other words,The curve reflects the micropore distribution of the sample soil, and it is found that when T2 is in 1.5~1.7ms, the pore distribution is the most.(4) the pore size distribution of the sample is measured by conventional mercury injection test. The larger the dry density is, the smaller the pore size is in the main pore distribution area of the sample. By comparing the two tests, it is found that the dry density mainly affects the content of macropores.The test results also show that the porosity of the soil is mainly macroporous, accounting for more than 80%.
【学位授予单位】：湖北工业大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TU41

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