管涌发展与悬挂式防渗墙作用机制研究

发布时间：2018-07-10 15:44

本文选题：管涌 + 土体内部侵蚀　；参考：《清华大学》2015年博士论文

【摘要】：管涌是威胁土石坝与堤防安全的重要隐患。由于它的发生难以预测、过程无法观测,为科学认识其物理现象和机制造成了较大困难。早在上个世纪初,已不断有学者的试验模拟、理论研究,但由于对细观侵蚀机制的研究仍不深入,仍然缺乏模拟管涌侵蚀发展过程、评估工程防控措施效果的数学模型方法。本文基于无粘性土中管涌侵蚀的细观力学机制开展研究,取得了如下成果:建立了考虑颗粒侵蚀和管涌通道尖端破坏机制的管涌侵蚀发展数学模型。该模型基于渗流-管流耦合的流场求解方法,考虑渗流作用力、颗粒自重及摩阻力的共同作用,模化侵蚀发生的力学机制。结合土体自身性质如级配曲线,孔隙度及渗透系数,考虑渗流侵蚀过程中的土-水耦合效应,提出以最大侵蚀量方向为判断管涌通道发展方向的依据,并以土体临界孔隙度作为判别管涌通道尖端侵蚀破坏的条件,确定土体内部侵蚀的侵蚀量。以符合土体内部侵蚀的泥沙侵蚀规律,确定管涌通道侵蚀发展的速率。同时,模型考虑了土体各向异性特性的影响。因此,模型可定量表达管涌通道尖端土体颗粒脱离骨架、被水流携带输移的细观物理机制,并可反映土体在不同密实度情况下发生管涌贯穿破坏的差异。应用经过验证的管涌动态发展模型,研究悬挂式防渗墙作用机制。发现悬挂式防渗墙使管涌通道发展过程分为三个阶段,绕墙段的发展由于侵蚀方向的改变,颗粒临界起动条件增大,是悬挂式防渗墙发挥作用的关键;同时,悬挂式防渗墙改变其周围局部流场,降低了当地土颗粒侵蚀的渗流作用力。如果潜在管涌发生点不在防渗墙的影响范围内,则防渗墙对管涌发生条件的影响微弱。此外,悬挂式防渗墙墙深、墙的位置以及土体渗透系数各向异性程度,都影响悬挂式防渗墙的渗控效果。通过对我国典型堤防的案例分析,发现工程中现有悬挂式防渗墙墙深经验公式(墙深为1-1.5倍水头)存在一定的适用条件,仅在墙深大于8米的情况下适用。同时,土颗粒级配、悬挂式防渗墙位置及土体密实程度均会影响悬挂式防渗墙的作用效果。
[Abstract]:Piping is an important hidden danger to the safety of earth-rock dams and levees. Because its occurrence is difficult to predict and the process can not be observed, it is difficult to understand its physical phenomena and mechanism scientifically. As early as the beginning of last century, there have been a lot of scholars' experimental simulation and theoretical research, but because the research on the mechanism of mesoscopic erosion is still not thorough, there is still a lack of mathematical model method to simulate the development process of piping erosion and to evaluate the effect of engineering prevention and control measures. In this paper, the mesomechanical mechanism of piping erosion in cohesive soils is studied, and the following results are obtained: a mathematical model of pipeline erosion development considering particle erosion and pipeline tip failure mechanism is established. The model is based on the coupled flow field solution of seepage and pipe flow, considering the interaction of seepage force, particle weight and frictional resistance, and the mechanical mechanism of modeling erosion. Considering soil properties such as gradation curve, porosity and permeability coefficient, considering the soil-water coupling effect in seepage erosion process, this paper puts forward that the direction of maximum erosion amount is the basis for judging the development direction of pipeline. The critical porosity of soil is taken as the condition of judging the erosion failure of the tip of the pipeline, and the erosion amount of the soil is determined. In order to accord with the law of soil erosion, the rate of erosion development of pipeline is determined. At the same time, the influence of soil anisotropy is considered in the model. Therefore, the model can quantitatively express the meso-physical mechanism that the soil particles at the tip of the pipeline break away from the skeleton and be transported by the water flow, and can reflect the difference of the penetration failure of the soil mass under different compactness. The mechanism of suspension cutoff wall is studied by using the proven dynamic development model of piping. It is found that the development process of the suspended cutoff wall can be divided into three stages, and the critical starting condition of the particles increases due to the change of the direction of erosion, which is the key to play the role of the suspended cutoff wall, and at the same time, The suspended cutoff wall changes the local flow field and reduces the seepage force of local soil particle erosion. If the potential piping occurrence point is not within the scope of the influence of the cutoff wall, the influence of the cutoff wall on the occurrence condition of the pipe surge is weak. In addition, the depth of the wall, the location of the wall and the anisotropy of the soil permeability coefficient all affect the seepage control effect of the suspended impermeable wall. Based on the analysis of typical levees in China, it is found that there are some applicable conditions for the existing empirical formula of wall depth of suspended impervious wall (the depth of wall is 1-1.5 times of water head), which can only be applied if the depth of wall is more than 8 meters. At the same time, the gradation of soil particles, the location of suspended cutoff wall and the compactness of soil will all affect the effect of suspension cutoff wall.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TV223.4

【相似文献】