基于常规试验的非饱和黄土强度参数的研究及应用

发布时间：2019-02-23 10:53

【摘要】：黄土是一种典型的非饱和土，我国黄土面积分布广泛，尤其是在西北部地区。在黄土地区地质灾害的发生多数情况下都与水的作用有关。因此非饱和黄土的强度参数测试与选取对评价黄土边坡的稳定性，防灾减灾具有重要的意义。本文以Bishop、Fredlund及Lu Ning的非饱和强度理论为依据，陕西省延安市延炼滑坡非饱和黄土为研究对象，采用不同含水率的常规试验——直剪试验与三轴试验，，测定了有效稳态强度参数，又用张力计测定了同一试样的水土特征曲线。再根据延炼滑坡恢复边坡，进行水分入渗数值模拟，及应力与稳定性分析，取得了以下成果： （1）取延炼滑坡Q2与Q1层黄土，配制不同的含水率作为原状土样，进行了固结慢剪试验和三轴CU试验，得到了不同含水率下黄土的强度参数粘聚力c和内摩擦角φ，分析发现含水率对黄土的抗剪强度有影响，而且对粘聚力的影响较大，对内摩擦角的影响不大。有效稳态粘聚力随含水率增大而降低，当含水率低于塑限时，有效稳态粘聚力随含水率增加显著降低。当含水率大于塑限时，有效稳态粘聚力趋于一稳定值，不再减小。有效稳态摩擦角与含水率没有明显的相关性，基本上是一个稳定的值，不随含水率的变化而变化。 （2）根据基质吸力试验得到黄土的土—水特征曲线，可以看出含水率与基质吸力的关系。基质吸力与含水率呈指数关系，随着含水率的增大，基质吸力逐渐降低。 （3）结合非饱和黄土强度参数与土水特征曲线，可以计算出非饱和土强度理论中Bishop的单变量理论强度参数χ和Fredlund的双变量理论φb。又根据Lu Ning提出的吸应力概念，得出了吸应力和体积含水率的关系曲线，即吸应力特征函数。并对这三种非饱和强度理论进行对比分析。Lu Ning的非饱和强度直接用吸应力函数表达，该强度公式回避了测定基质吸力的问题，便于在工程实际中推广。 （4）针对延炼滑坡滑动前地形，通过Geo-studio软件建立数值模型，模拟水分入渗时边坡土体内水位线及孔隙水压力随时间的变化。再利用非饱和土抗剪强度公式，并结合本文试验得出的非饱和黄土公式强度参数，计算蒸气冷凝入渗时边坡滑面上抗剪强度，以及边坡的稳定性。
[Abstract]:Loess is a typical unsaturated soil. Loess is widely distributed in China, especially in northwest China. The occurrence of geological disasters in loess area is mostly related to the action of water. Therefore, the test and selection of the strength parameters of unsaturated loess is of great significance to evaluate the stability of loess slope and to prevent and reduce the disaster. Based on the unsaturated strength theory of Bishop,Fredlund and Lu Ning, the unsaturated loess of Yanlian landslide in Yanan City, Shaanxi Province is taken as the research object. The conventional tests of different moisture content, direct shear test and triaxial test, are adopted in this paper. The effective steady-state strength parameters were measured, and the soil and water characteristic curves of the same sample were measured by the tensometer. According to the slope restoration of Yanlian landslide, the numerical simulation of water infiltration and the analysis of stress and stability are carried out. The following results are obtained: (1) taking the loess of Q2 and Q1 layers of Yan-Lian landslide, different moisture content is prepared as undisturbed soil sample. The consolidation slow shear test and triaxial CU test were carried out, and the cohesive force c and internal friction angle 蠁 of loess strength parameters under different moisture content were obtained. It was found that moisture content had an effect on the shear strength of loess, and had a great effect on cohesion. It has little effect on the angle of internal friction. The effective steady-state cohesion decreases with the increase of moisture content. When the moisture content is lower than the plastic limit, the effective steady-state cohesion decreases significantly with the increase of moisture content. When the moisture content is larger than the plastic limit, the effective steady-state cohesive force tends to a stable value and no longer decreases. There is no obvious correlation between the effective steady state friction angle and the moisture content, which is basically a stable value and does not change with the change of the moisture content. (2) the soil-water characteristic curve of loess is obtained by the matrix suction test, and the relation between the moisture content and the matrix suction can be seen. The matrix suction was exponentially related to the moisture content, and the matrix suction decreased gradually with the increase of the moisture content. (3) combining the strength parameters of unsaturated loess with soil-water characteristic curves, the univariate theoretical strength parameter 蠂 of Bishop and the bivariate theory of 蠁 b of Fredlund can be calculated in unsaturated soil strength theory. According to the concept of absorptive stress put forward by Lu Ning, the curve of relation between suction stress and volume moisture content is obtained, that is, the characteristic function of absorptive stress. The three theories of unsaturated strength are compared and analyzed. The unsaturated strength of. Lu Ning is expressed directly by the absorptive stress function. The strength formula avoids the problem of measuring the suction of matrix and is easy to be popularized in engineering practice. (4) according to the topography of Yanlian landslide before sliding, a numerical model was established by Geo-studio software to simulate the variation of soil water level and pore water pressure with time during the infiltration of water. Then the shear strength formula of unsaturated soil and the strength parameters of unsaturated loess formula obtained in this paper are used to calculate the shear strength on the slip surface of the slope and the stability of the slope.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU444

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