重塑网纹红土非饱和直剪强度特性的微结构效应研究

发布时间：2018-05-06 00:08

本文选题：重塑网纹红土 + 直接剪切　；参考：《合肥工业大学》2017年硕士论文

【摘要】：网纹红土是宣城地区广泛分布的具有特殊结构的黏性土,以往针对网纹红土强度的研究主要为饱和强度,而针对重塑土非饱和强度和微结构的研究则相对较少。宣城网纹红土多处于非饱和状态,故开展非饱和网纹红土强度研究,对确保网纹红土场地工程建设安全具有重要意义。论文基于非饱和土直剪实验系统研究了基质吸力和净法向应力对非饱和重塑网纹红土的强度规律,并基于Fredlund和Bishop非饱和强度公式分析了相应非饱和强度参数变化规律,进而通过扫描电子显微镜(SEM)和能谱仪(EDS)分析了剪切破坏面上土体的微结构定量变化,以探究微结构特征与宏观强度和变形的联系。论文得到如下的主要结论:(1)重塑网纹红土非饱和试验结果表明,试样破坏形式可表现为脆性和塑性破坏,但脆性破坏一般出现在高基质吸力和低净法向应力的试验条件下,而塑性破坏的条件正好与之相反。(2)基于Fredlund强度公式的分析表明:重塑网纹红土在不同基质吸力条件下的黏聚力随着基质吸力的增大并非逐渐增大,且基质吸力对应的内摩擦角也不随着基质吸力的增大而增大;在基质吸力为100k Pa以下,黏聚力随着基质吸力的提高而逐渐增大,基质吸力对应的内摩擦角逐渐减小;而在基质吸力大于200k Pa以上,黏聚力和基质吸力对应的内摩擦角均随着基质吸力的提高而增大,净法向应力对应的内摩擦角却随着基质吸力的增大而逐渐增大。(3)基于Bishop强度公式的分析表明:有效应力参数并非一个[0,1]的数值,在当基质吸力大于等于200k Pa时,该参数基本不再随着净法向应力的变化而变化,总体上趋于一个与净法向应力有关的定值;当基质吸力小于200k Pa时,该参数的变化规律与净法向应力有关,在净法向应力为200k Pa、300k Pa的条件下随着净法向应力的增大而减小,当净法向应力变为100k Pa、410k Pa时随着净法向应力的增大而增大。(4)基于试验实测数据,应用Matlab分析了非饱和强度、基质吸力和净法向应力三者的关系,发现三者存在着曲面关系,与Fredlund公式表达的平面关系存在差别,该曲面体现了重塑网纹红土强度在净法向应力为100k Pa和200k Pa、基质吸力为100k Pa和200k Pa处出现明显变化,这一现象也同时表明了Fredlund公式对试验用土的强度适用性存在一定局限性。(5)SEM和EDS试验分析结果表明:重塑直剪试样剪切面上的孔隙主要以0.1~0.2μm2的孔隙为主,0.02~0.1μm2和大于等于0.2μm2的孔隙次之,此与原状土样的微孔隙特征存在较大区别,可能与试验土样经磨细过筛后的重塑处理有关;网纹红土主要有氧、铝、硅、铁以及少量的钾、镁和钙等化学元素。(6)微结构的定量研究发现,在基质吸力为200k Pa和350k Pa条件下试样剪切面上出现了凸起的山脊状微结构。经过对比分析,该微结构可能是出现摩擦划痕形态前形成的一种微结构形式,而且与净法向应力的大小无关。
[Abstract]:Reticulated red soil is a kind of clay with special structure widely distributed in Xuancheng area. In the past, the research on the strength of reticulated red soil was mainly saturation strength, but the research on unsaturated strength and microstructure of remolded soil was relatively less. Most of the reticulated red soil in Xuancheng is in unsaturated state, so it is of great significance to study the strength of the unsaturated reticulated laterite to ensure the safety of the site construction. Based on the direct shear experiment of unsaturated soil, the strength law of matrix suction and net normal stress on unsaturated remolded reticulated red soil is studied in this paper, and the variation law of unsaturated strength parameters is analyzed based on Fredlund and Bishop unsaturated strength formula. Then the quantitative changes of soil microstructure on the shear failure surface were analyzed by scanning electron microscopy (SEM) and energy spectrometer (EDS) in order to explore the relationship between microstructure characteristics and macroscopic strength and deformation. The main conclusions of the paper are as follows: (1) the unsaturated test results of remolded reticulated red soil show that the failure forms of the specimens may be brittle and plastic failure, but the brittle failure usually occurs under the conditions of high matrix suction and low net normal stress. On the other hand, the plastic failure condition is just the opposite. (2) the analysis based on Fredlund strength formula shows that the cohesion of remolded reticulated red soil does not increase with the increase of matrix suction under different matrix suction conditions. The internal friction angle of matrix suction does not increase with the increase of matrix suction, and the cohesion increases gradually with the increase of matrix suction, and the internal friction angle of matrix suction decreases gradually with the increase of matrix suction. However, when the matrix suction is larger than 200 KPA, the internal friction angle corresponding to the cohesion and the matrix suction increases with the increase of the matrix suction. The internal friction angle corresponding to the net normal stress increases gradually with the increase of the matrix suction. The analysis based on the Bishop strength formula shows that the effective stress parameter is not a value of [0 ~ 1], when the matrix suction is greater than 200 KPA, The parameter does not change with the change of net normal stress, and generally tends to a fixed value related to net normal stress, and when the matrix suction is less than 200 KPA, the variation of this parameter is related to net normal stress. Under the condition that the net normal stress is 300kPa, the net normal stress decreases with the increase of the net normal stress, and the net normal stress increases with the increase of the net normal stress when the net normal stress becomes 100kPa410kPa.) based on the experimental data, the unsaturated strength is analyzed by Matlab. The relationship between matrix suction and net normal stress shows that there is a curved surface relationship among them, and there is a difference between them and the plane relation expressed by Fredlund formula. The surface shows that the strength of remolded reticulated red soil varies obviously at the net normal stress of 100kPa and 200kPa, and the matrix suction of 100kPa and 200kPa. This phenomenon also indicates that the applicability of Fredlund formula to the strength of soil is limited. The results of SEM and EDS test show that the porosity in shear plane of remolded specimens is mainly 0. 1 0. 2 渭 m ~ 2 and 0. 1 渭 m ~ (2) or larger than that of 0. 1 0. 2 渭 m ~ (2). The porosity of 0.2 渭 m ~ 2 is the second, This is different from the micropore characteristics of the undisturbed soil, and may be related to the remolding of the test soil samples after grinding and sifting; the reticulated laterite is mainly aerobic, aluminum, silicon, iron and a small amount of potassium. A quantitative study of the microstructure of magnesium and calcium, and other chemical elements. It was found that the ridge structure appeared on the shear surface of the sample under the conditions of 200 KPA and 350 KPA matrix suction. The microstructures may be formed before the appearance of friction scratches and are independent of the size of the net normal stress.
【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】：TU442

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