不同应力路径下的合肥膨胀土非饱和特性研究

发布时间：2018-07-03 04:00

本文选题：非饱和土 + 膨胀土　；参考：《合肥工业大学》2015年硕士论文

【摘要】：膨胀土广泛分布于合肥地区,具有水分敏感性和吸水膨胀失水收缩的特性,其非饱和特性在不同应力路径下表现不同,故研究不同应力路径下的非饱和膨胀土力学性质具有重要的意义和工程价值。论文基于合肥原状膨胀土试样,首先基于XRD、能谱仪实验(EDS)和基本力学实验分析了实验用土的成分和物理力学特性；应用GDS三轴实验仪器研究了剪切速率、吸力、于湿循环等因素对非饱和强度和变形的影响,以及不同应力路径下非饱和特性,采用扫面电镜(SEM)实验分析了剪切前、后的膨胀土体的微观结构,进而应用数字图像处理技术进行定量表征,并探讨了微观结构的变化与宏观力学性能之间的关系,得出以下的主要结论：(1)实验用土的液塑限、最优含水量分别为45%、27.1%和14.78%；XRD实验表明实验用土粘土矿物以蒙脱石和伊利石为主；EDS分析膨胀土中的矿物元素主要是氧、硅、铝、铁四种元素。(2)无侧限抗压强度峰值约为610kPa,并随含水量的增加而减小,峰值强度对应的轴向应变则随含水量的增大而增大,对应的轴向应变多在3%以下。(3)三轴非饱和强度实验表明,实验用土的非饱和抗剪切强度随着吸力和剪切速率的增大而增大,但随干湿循环次数的增加而降低。(4)加轴压应力路径可以改善膨胀土体的抗剪切性质,加轴压应力路径的抗剪切强度峰值与无路径的情况下基本相同,但峰值强度对应的轴向应变则比无路径的情况下减少50%以上：减围压应力路径下非饱和膨胀土体的抗剪切强度峰值比无路径的情况下降低20%～50%左右,且在剪切过程中很快的达到峰值强度；不同路径下膨胀土体剪切破坏后残余强度和峰值强度相差不大,且残余强度随着轴向变形的增加不发生明显的降低；不同路径下膨胀土体剪切过程中体积变化很小,变化率在2%的范围内,不发生剪胀现象。(5)SEM试验发现合肥地区原状膨胀土样以层状结构和紊流结构为主,干湿循环会破坏土体的微观结构。微孔隙面积大多分布在5-20umn2附近,周长多分布在10-20umn附近。剪切后土体的孔隙被明显的压密,微孔隙的周长、面积和直径的平均值变化不大。剪切后微孔隙面积在5um2附近的微孔隙几乎全部被压密消失。
[Abstract]:Expansive soil is widely distributed in Hefei, which has the characteristics of water sensitivity and water absorption, expansion and loss of water, and its unsaturated characteristics are different under different stress paths. Therefore, it is of great significance and engineering value to study the mechanical properties of unsaturated expansive soils under different stress paths. Based on the sample of undisturbed expansive soil in Hefei, the composition and physical and mechanical properties of the soil were analyzed by XRD, EDS and basic mechanical experiments, and the shear rate and suction were studied by GDS triaxial test instrument. Under the influence of wet cycle and other factors on unsaturated strength and deformation, as well as the unsaturated characteristics under different stress paths, the microstructure of expansive soil before and after shearing was analyzed by scanning electron microscopy (SEM). Then the quantitative characterization was carried out by using digital image processing technology, and the relationship between the change of microstructure and the macroscopic mechanical properties was discussed. The main conclusions were as follows: (1) the liquid plastic limit of the experimental soil, the optimum water content was 450.71% and 14.78%, respectively; XRD results show that the clay minerals used in the experiment are mainly montmorillonite and Illite to analyze the mineral elements of expansive soil mainly oxygen, silicon, aluminum and iron. (2) the peak value of unconfined compressive strength is about 610kPaand decreases with the increase of water content. The axial strain corresponding to the peak strength increases with the increase of water content, and the corresponding axial strain is below 3%. (3) the experimental results show that the unsaturated shear strength of the soils increases with the increase of suction and shear rate. However, with the increase of dry and wet cycles, the shear resistance of expansive soil can be improved by adding axial compression stress path, and the peak value of shear strength of axial compression stress path is basically the same as that without path. However, the axial strain corresponding to peak strength is reduced by more than 50% compared with that without path, and the peak shear strength of unsaturated expansive soil under reduced confining stress path is about 20% lower than that without path. The residual strength and peak strength of expansive soil after shear failure have little difference under different paths, and the residual strength does not decrease obviously with the increase of axial deformation. The volume change of expansive soil in different paths is very small, and the change rate is within 2%. (5) SEM test shows that the undisturbed expansive soil samples in Hefei area are mainly stratified and turbulent. Dry and wet circulation will destroy the microstructure of soil. The micropore area is mostly distributed near 5-20umn2, and the circumference is mostly near 10-20umn. After shear, the pores of soil are obviously compacted, and the average values of perimeter, area and diameter of micropores are not changed much. After shearing, almost all the micropores near 5um2 are disappeared by compaction.
【学位授予单位】：合肥工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU433

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