堤基侵蚀型管涌的砂槽试验研究

Study on the Piping Erosion in Levee Foundation by Sand Box Model Test

堤基侵蚀型管涌是汛期堤防工程中常见的一种渗透变形现象,其发生完全位于堤基或坝体内部,通常不易被发现,难以及时采取相应措施予以控制。同时,随着侵蚀型管涌的发展,堤基进一步会产生不均匀沉降,最终威胁大坝的安全,因而其发展机理和破坏特性的研究一直是国内外研究的热点和难点。为探究堤基侵蚀型管涌的发生发展过程及破坏规律,通过引入多色填充砂示踪方法实现了对土样中填充细料颗粒运移的顺序和方向进行判别,从而更直观地揭示管涌发展过程。根据不同管涌土判别方法选取了3种间断级配的土样进行侵蚀型管涌双层堤基砂槽模型试验,并对现有管涌土判别方法的有效性进行了比较。同时,考虑变水头条件和土料级配两种因素对管涌侵蚀结果的影响,分析"扰动"作用与管涌发展的关系。通过研究表明:侵蚀型管涌破坏始于管涌口周围的细料流失,随着渗透侵蚀的发展,细料起动和流失位置均逐渐向上游发展;侵蚀过程中细料的流失具有明显的渐进性,而细料起动可以发生在侵蚀范围之外;外部因素或渗流稳定因素造成的"扰动"作用对侵蚀型管涌过程具有促进作用。

Embankment piping erosion is a common infiltration deformation in flood embankment projects.Its occurrence is completely inside the embankment or dam body.It is usually not easy to find and it is difficult to take timely measures to control it.At the same time,with the development of the eroded pipe,the embankment will further produce uneven settlement and finally threaten the safety of the dam.Therefore,the research on its development and failure characteristics has been a hot and difficult topic.In order to explore the occurrence and development of eroded pipe pits and the failure rules,the multi-color sand-filling tracer method was used to distinguish the order and direction of the fine particles migration in the soil samples so as to reveal the development of piping in a more direct way.Three types of intermittent gradation soil samples are selected,according to different discriminant method of soil pip- ing,and a model test of double-layer dike foundation in a flume is used to conduct the test.The effectiveness of the existing methods for determining soil piping were compared to each other.In the same time,considering the influence of water head and material grada- tion on the results of piping erosion,the relationship between＂disturbance＂and piping development was analyzed.It is shown that the piping erosion begins with the loss of fine particles around the piping outlet.With the further development of erosion,the starting point and the loss of fine material are gradually moved to the upstream.The study also shows that the loss of fine particles in the process of erosion is progressive obviously and the starting of loss can occur outside of erosion range.The external factors or seepage stability factors that lead to＂disturbance＂have the effect of enhancing the process of piping erosion.