降雨入渗对黄土开挖边坡稳定性影响的研究

发布时间：2018-05-01 12:39

本文选题：黄土边坡 + 降雨入渗　；参考：《西北农林科技大学》2017年硕士论文

【摘要】：滑坡是我国主要的地质灾害之一。在黄土分布广泛的西北和华北地区,大量的建设工程在实施过程中会形成大量的黄土开挖边坡,如何避免滑坡的发生成了当前的重点和难点。近年来,持续的强降雨等恶劣的极端气象灾害频繁发生,进一步加大了滑坡发生的概率。本文以延安市治沟造地工程为例,通过野外调查、室内试验、边坡稳定数值模拟计算研究了开挖边坡的滑坡形成机理。工程区夏季持续的强降雨天气导致边坡在坡顶、平台、坡脚处汇集积水。针对这一现象,重点研究了持续强降雨引起的积水入渗对边坡稳定性的影响。通过在室内模拟土体垂直方向一维降雨积水入渗过程,观测分析了土体含水率的变化以及湿润锋运移的特征。通过室内剪切试验,研究了含水率变化对边坡土体抗剪强度的影响。根据降雨积水入渗试验得到的不同时刻土体饱和区分布情况,结合饱和区土体重度、粘聚力、内摩擦角的具体数值,采用FLAC3D岩土工程数值计算软件计算分析了持续降雨条件下边坡的安全稳定性以及潜在滑动面的变化情况。最后针对开挖边坡在自然状态下的稳定性,通过计算不同坡型与坡比下坡体的安全系数研究了边坡开挖方式的优化。本文得到的主要结论如下:(1)土体垂直方向一维积水入渗试验结果表明:在降雨积水入渗条件下,浅层土体中湿润锋运移速度较快,随着深度的增加湿润锋运移速度逐渐减缓;当湿润锋到达时,不同深度土体含水率均呈现先陡升再趋于平缓上升的变化;入渗持续一定时间后,某一深度土体的含水率基本保持不变,饱和度可达80%。(2)对比分析强度折减法的三种失稳判据可得:数值计算不收敛判据的求解过程高效,简便快捷;特征部位位移突变判据的求解过程繁琐,但该判据得到的安全系数精确度较高;塑性区贯通判据求解过程能直观反映剪切带发展过程,但该判据得到的安全系数精确度不高。三种判据各有优势,但结合三种判据共同进行安全系数的计算能全面掌握边坡稳定性。(3)降雨入渗使土体的抗剪强度显著降低,随着降雨历时的增加,边坡土体中的饱和区域增大,土体局部的剪切变形增大。局部发生的塑性变形逐步扩展到一定程度时,坡体会产生位移突变以及剪切应变增量突变进而形成贯通的剪切带,从而导致滑坡。因此,黄土边坡应设置排水措施,避免降雨入渗引发滑坡等自然灾害。(4)通过计算开挖边坡在自然状态时不同坡型与坡比下的安全系数,证实了在坡体中间增设平台能够提升边坡的安全系数,增大边坡的稳定性。在边坡顶点和坡脚位置固定的情况下,随着平台宽度的增加,边坡安全系数呈现先增大后减小的变化情况。因此建议工程实际中合理增设平台,控制平台宽度。
[Abstract]:Landslide is one of the main geological disasters in China. In the Northwest and North China, where loess is widely distributed, a large number of construction projects will form a large number of loess excavation slopes in the process of implementation. How to avoid the occurrence of landslides has become the focus and difficulty. In recent years, severe extreme weather disasters such as continuous heavy rainfall occur frequently, which further increases the probability of landslide occurrence. In this paper, the landslide formation mechanism of excavated slope is studied by field investigation, laboratory test and numerical simulation calculation of slope stability, taking Yanan City Zhigou Land Reclamation Project as an example. The continuous heavy rainfall in summer in the engineering area leads to the accumulation of water at the top, platform and foot of the slope. In view of this phenomenon, the influence of water infiltration caused by continuous heavy rainfall on slope stability is studied. By simulating the infiltration process of one-dimensional rainfall water in vertical direction, the variation of soil moisture content and the characteristics of wetting front migration were observed and analyzed. The influence of water content on the shear strength of slope soil was studied by indoor shear test. According to the distribution of saturated soil at different times, the specific values of soil mass, cohesive force and internal friction angle in saturated area are obtained by rainfall water infiltration test. The safety and stability of slope and the variation of potential sliding surface under the condition of continuous rainfall are calculated and analyzed by FLAC3D geotechnical engineering numerical calculation software. Finally, aiming at the stability of excavation slope under natural condition, the optimization of slope excavation mode is studied by calculating the safety factor of slope body with different slope types and slope ratio. The main conclusions of this paper are as follows: (1) the results of one-dimensional water infiltration test in vertical direction show that under the condition of rainfall water infiltration, the velocity of wetting front migration in shallow soil is faster, and the migration velocity of wetting front gradually slows down with the increase of depth; When the wetting front arrives, the moisture content of the soil at different depths is steeply rising and then tends to rise slowly, and the moisture content of the soil at a certain depth remains basically unchanged after the infiltration lasts for a certain time. Saturation can reach 80. 2) three kinds of instability criteria for comparing and analyzing strength reduction method can be obtained: the calculation process of numerical calculation non-convergence criterion is efficient, simple and fast, and the calculation process of displacement catastrophe criterion of characteristic position is complicated. However, the accuracy of safety factor obtained by this criterion is high, and the calculation process of plastic zone penetrating criterion can directly reflect the development process of shear band, but the accuracy of safety factor obtained by this criterion is not high. Each of the three criteria has its own advantages, but the calculation of the safety factor combined with the three criteria can fully grasp the slope stability. 3) rainfall infiltration can significantly reduce the shear strength of soil, and with the increase of rainfall duration, The local shear deformation of the slope increases with the increase of the saturated area. When the local plastic deformation gradually extends to a certain extent, the slope experience the displacement abrupt change and the shear strain increment abrupt change to form the through shear zone, thus causes the landslide. Therefore, drainage measures should be set up in loess slope to avoid natural disasters such as landslide caused by rainfall infiltration. It is proved that adding a platform in the middle of the slope can enhance the safety factor of the slope and increase the stability of the slope. When the position of the top and foot of the slope is fixed, the slope safety coefficient increases first and then decreases with the increase of the platform width. Therefore, it is suggested that the platform should be added reasonably and the width of the platform should be controlled.
【学位授予单位】：西北农林科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU43

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