非饱和黄土本构模型研究

发布时间：2018-03-22 09:18

本文选题：黄土　切入点：非饱和土　出处：《长安大学》2016年博士论文　论文类型：学位论文

【摘要】：黄土是典型的非饱和土,黄土的非饱和本构模型是黄土工程特性研究的一个重要方向。本文采取了陕西泾阳南塬L5黄土,开展了系统地试验研究。陕西泾阳南塬黄土地层剖面出露完整,剖面可见S0到L9全部地层,受农业灌溉影响,该黄土塬北缘滑坡发育,且属于典型黄土层内滑坡。此次试验所取L5试样(Q2)位于该处滑坡的主要剪切带,为典型的非饱和结构性黄土。本文通过试验取得了该黄土的物理力学参数,建立了能够反映黄土变形特性的非饱和本构模型,开展的主要工作如下:(1)将L5原状样和分层击实所得重塑样分别配制8%、11%、15%、20%和25%五个不同含水率,采用常规三轴仪在100 kPa、200 kPa、300 kPa、400 kPa和500 kPa五个不同围压下进行CD试验。试验结果表明有效稳态摩擦角与含水率无明显相关性,基本为一稳定值。含水率低于塑限时,有效稳态粘聚力随含水率增大而显著降低;当含水率高于塑限时,有效稳态粘聚力不再随含水率的增大而降低,趋于一稳定值。(2)利用三轴CD试验,结合Fredlund SWCC压力板仪测得的土水特征曲线,分析了Fredlund、Bishop和Lu Ning三种非饱和土强度表达式中的强度参数。其中Bishop和Fredlund强度公式中的参数χ和υb必须利用土水特征曲线确定;而Lu Ning强度公式中的吸应力与含水率的关系,可通过不同含水率常规三轴试验确定,这回避了基质吸力测定的不便,便于在工程实际中推广应用。(3)根据不同含水率不同围压原状和重塑土常规三轴CD试验所得变形和强度参数变化规律,得到不同含水率下L5原状和重塑试样的理想弹塑性模型,并对模型的适用性进行了验证,并结合对应含水率下原状及重塑土的K0固结试验结果,对Duncan-Chang非线性弹性模型中的μ的表达式进行修改,得到了原状及重塑黄土非饱和非线性弹性模型的表达式,并进行了验证。(4)通过对初始孔隙比相同的L5重塑和原状试样进行不同含水率的固结试验,发现在半对数坐标系下不同含水率试样的膨胀回弹线相互平行,固结压缩线的直线段也相互平行,压缩线的斜率λ较膨胀回弹线κ更陡;相同应力条件下,试样的初始含水率越高,孔隙比越小;相同应力条件下,原状土相对应重塑土而言能保持更大的孔隙比。(5)本文基于修正剑桥模型,通过半对数坐标下非饱和重塑样与饱和重塑样固结曲线的关系,引入非饱和状态变量ρss代表相同平均骨架应力下非饱和与饱和状态重塑样孔隙比的差值。并结合超固结状态变量ρe推导出了能够反映非饱和重塑黄土超固结特性的本构模型。(6)基于黄土非饱和重塑本构模型,引入结构性状态变量ρst代表固结试验半对数坐标系中相同平均骨架应力和饱和度下原状与重塑黄土孔隙比的差值,推导出了更够反映结构性的适用于原状黄土的非饱和本构模型。
[Abstract]:Loess is a typical unsaturated soil, and the unsaturated constitutive model of loess is an important direction in the study of loess engineering characteristics. A systematic experimental study has been carried out. The profile of the loess layer in the southern plateau of Jingyang, Shaanxi Province, is completely exposed, and all strata from S0 to L9 can be found in the section. The landslide in the northern margin of the loess plateau is developed under the influence of agricultural irrigation. The L5 sample Q2), which is located in the main shear zone of the landslide, is a typical unsaturated structural loess. The physical and mechanical parameters of the loess are obtained by experiments. An unsaturated constitutive model which can reflect the deformation characteristics of loess is established. The main work is as follows: (1) eight different moisture contents are prepared from L5 undisturbed sample and remolded sample from stratified compaction, respectively, of 8% and 25%, respectively. The CD test was carried out under five different confining pressures of 100kPa200kPa200kPa300kPa400 kPa and 500kPa300KPA by conventional triaxial apparatus. The experimental results show that there is no obvious correlation between the effective steady-state friction angle and the moisture content, which is basically a stable value, and when the moisture content is below the plastic limit, When the moisture content is higher than the plastic limit, the effective steady-state cohesion decreases no longer with the increase of moisture content, and tends to a stable value. Based on the soil-water characteristic curve measured by Fredlund SWCC pressure plate, the strength parameters of Fredlundbin Bishop and Lu Ning are analyzed. The parameters 蠂 and u b in Bishop and Fredlund strength formulas must be determined by soil-water characteristic curve. However, the relationship between absorption stress and moisture content in Lu Ning strength formula can be determined by conventional triaxial test of different moisture content, which avoids the inconvenience of matrix suction measurement. It is easy to be popularized and applied in engineering practice. According to the variation law of deformation and strength parameters obtained from conventional triaxial CD test of different moisture content and different confining pressure, the ideal elastic-plastic model of L5 undisturbed and remolded specimens under different moisture content is obtained. The applicability of the model is verified, and the expression of 渭 in the Duncan-Chang nonlinear elastic model is modified by combining the K0 consolidation test results of the undisturbed and remolded soils under the corresponding moisture content. The expressions of unsaturated nonlinear elastic model of undisturbed and remolded loess are obtained, and verified by the consolidation tests of L5 remolded and undisturbed specimens with the same initial void ratio. It is found that in the semi-logarithmic coordinate system, the expansion springback lines of samples with different moisture content are parallel to each other, and the straight lines of the consolidation and compression lines are parallel to each other, and the slope 位 of the compression lines is steeper than that of the swelling and springback lines, and under the same stress conditions, The higher the initial moisture content of the sample, the smaller the void ratio; under the same stress condition, the undisturbed soil can keep a larger void ratio for the remolded soil. According to the relationship between unsaturated remolded sample and saturated remolded sample consolidation curve in semi-logarithmic coordinate, The unsaturated state variable 蟻 ss is introduced to represent the difference between unsaturated and saturated remolded void ratio under the same mean skeleton stress. Combining with the overconsolidated state variable 蟻 e, the overconsolidation characteristics of unsaturated remolded loess are derived. Based on the unsaturated remolded constitutive model of loess, The structural state variable 蟻 st is introduced to represent the difference between original and remolded loess void ratio under the same mean skeleton stress and saturation in the semi-logarithmic coordinate system of consolidation test. An unsaturated constitutive model suitable for undisturbed loess is derived.
【学位授予单位】：长安大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P642.131

【相似文献】