天水非饱和原状黄土的变形强度及渗气特性研究

发布时间：2018-05-14 22:23

本文选题：非饱和黄土 + 三轴试验　；参考：《西安理工大学》2017年硕士论文

【摘要】：黄土是具有水敏性的特殊土,天然状态的黄土大多处于非饱和状态。在黄土地区的实际工程中,不同的开挖及回填方式会让土体经历不同的应力路径,进一步影响土体的变形强度及屈服特性。气体渗透系数是非饱和土固结分析的参数之一,气体渗透系数受干密度、含水率的影响。应力状态也对土体渗气特性产生影响。研究黄土在不同应力路径下变形、强度、屈服及渗气特性具有重要的理论及实际意义。论文首先对原状黄土进行了控制吸力的等向压缩、常规三轴压缩以及等应力比压缩试验。基于等向压缩试验,分析了变形及屈服特性,研究了吸力对变形特性指标的影响,弹性指数随吸力的变化基本不变,压缩指数随吸力的增大而增大;屈服应力随吸力的增大而增大。基于常规三轴压缩试验,分析了吸力对变形强度及屈服特性,应力应变关系呈硬化型,非饱和黄土强度符合Fredlund强度准则。基于等应力比压缩试验,分析了吸力、应力比对变形及屈服特性指标的影响,研究表明,同一吸力状态下,相同轴向变形时,偏应力随应力比的增大而增大,相同吸力时,弹性指数随应力比的变化基本不变,压缩指数随应力比的增大而增大。相同应力比时,弹性指数、压缩指数皆随吸力的增大而增大。基于三种应力路径下的试验结果,得到在q-p平面内的屈服线并非对称于p轴,而是对称于k0线,并提出屈服线的数学表达式。其次,进行了等向压缩及三轴压缩应力条件下的渗气试验。研究了含水率、饱和度、净平均应力、固结围压、剪应力水平以及应力产生的孔隙比等因素对渗气系数的影响,结果表明:相同含水率时,渗气系数随净平均应力与固结应力以及剪应力水平的增大而减小;相同净平均应力时,渗气系数随含水率与饱和度的增大而减小;相同含水率时,渗气系数随应力引起孔隙比的增大而减小;且同一含水率,不同固结围压、剪应力水平下的ka~e关系点分布在一带状区域内,可以归一。不同含水率、固结围压、剪应力水平下渗气系数与修正气体饱和度可以归一并建立起数学表达式。
[Abstract]:Loess is a special soil with water sensitivity, and the natural loess is mostly in unsaturated state. In the actual engineering of loess area, different excavation and backfill methods will make the soil go through different stress paths, which will further affect the deformation strength and yield characteristics of the soil. The gas permeability coefficient is one of the parameters in the consolidation analysis of unsaturated soil. The gas permeability coefficient is affected by dry density and moisture content. The stress state also affects the gas permeability of soil. It is of great theoretical and practical significance to study the deformation, strength, yield and gas permeability of loess under different stress paths. In this paper, the isotropic compression, conventional triaxial compression and iso-stress ratio compression tests of undisturbed loess are carried out. Based on the isotropic compression test, the deformation and yield characteristics are analyzed, and the influence of suction on the deformation characteristics is studied. The elastic index is basically unchanged with the suction, and the compression index increases with the increase of the suction. The yield stress increases with the increase of suction. Based on the conventional triaxial compression tests, the deformation strength and yield characteristics of suction are analyzed. The stress-strain relationship is of hardening type, and the strength of unsaturated loess conforms to the Fredlund strength criterion. Based on the compression test of equal stress ratio, the effects of suction, stress ratio on deformation and yield characteristics are analyzed. The results show that under the same suction state and the same axial deformation, the deflection stress increases with the increase of stress ratio, and with the same suction, the deflection stress increases with the increase of stress ratio. The elastic exponent is almost unchanged with the stress ratio, and the compression index increases with the increase of the stress ratio. At the same stress ratio, the elastic exponent and compression exponent increase with the increase of suction. Based on the experimental results under three stress paths, it is obtained that the yield line in the q-p plane is not symmetric to the p axis, but to the k _ 0 line, and the mathematical expression of the yield line is presented. Secondly, the gas permeation tests were carried out under isotropic compression and triaxial compression stress. The effects of water content, saturation, net mean stress, consolidation confining pressure, shear stress level and void ratio produced by stress on permeability coefficient are studied. The permeability coefficient decreases with the increase of net average stress, consolidation stress and shear stress level; at the same net average stress, the permeability coefficient decreases with the increase of water content and saturation; at the same water content, the permeability coefficient decreases with the increase of water content and saturation. The permeability coefficient decreases with the increase of void ratio caused by stress, and the ka~e relation points of the same water content, different consolidation confining pressure and shear stress level are distributed in a zonal region, which can be reunified. The mathematical expressions of permeability coefficient and modified gas saturation under different water content, consolidation confining pressure, shear stress level and modified gas saturation can be established.
【学位授予单位】：西安理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU444

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