Embankment Failures and Slope Protection of Earth Dams during Flooding

通过离心机模型试验，研究了洪水过程中水库蓄水迅速增加引起土坝渗透破坏的机理，了解哪种因素是土坝破裂的主要触发因素，以及它在堤防整体破坏过程中的作用时间和作用方式。在室内模型试验中实现渗透破坏的可行性是今后土石坝水力劈裂研究的另一个重要课题。通过几个不同压实条件下的模型土坝的试验，考察了它们对填土中孔压发展的影响，发现洪水期间水库水量迅速增加导致堤防破坏的两种不同模式。一种是在干燥和压实不良的填土情况下，其中渗水流经坝体的内部侵蚀(管道)占主导地位，尽管溢流水最初会因沟槽侵蚀而对下游表面造成轻微破坏，并引发管道。另一种是在淹水前填土处于潮湿和/或高度压实状态的情况下，由于水的过度流动而导致的地表沟槽侵蚀以恒定的速度向上游延伸，内部侵蚀很少。孔压的测量和模型试验的有限元分析在一定程度上揭示了这些路堤破坏的机理，但还需要进一步的研究来给出更精确和定量的讨论。针对防洪护坡工程，进行了几个模型试验，探讨了采用什么材料、在哪里施工以及如何施工才能获得更有效的防护效果。如何将其应用于堤防的实际设计和施工中，还有待于进一步的探讨。

Centrifuge model tests were carried out in order to investigate the mechanism of seepage failures of earth dams caused by a rapid increase of reservoir water during flooding, to know which factor should be the main trigger of fracture and when and how it works in the process of overall failure of the embankment. Feasibility of realizing seepage failures in laboratory model tests is another important subject to be discussed for future studies on hydraulic fracturing in earth and rockfill dams. Tests were conducted on several model earth dams made under different compaction conditions to examine their influence on the development of pore-water pressure in the fill.Two distinct patterns were noticed in embankment failures caused by a rapid increase of reservoir water during flooding. One is in case of dry and poorly compacted fill where internal erosion (piping) due to seepage water flow through the dam body is predominant, though over-flow water initially causes a little damage to the downstream surface by gully erosion and contributes to a trigger of piping. The other is in case of fill in wet and/or highly compacted state before flooding, in which surface gully erosion due to over-flow of water extends in a constant rate to the upstream side with a little internal erosion. Measurement of pore-water pressure and FEM analysis on the model tests somewhat revealed the mechanism of these embankment failures, though further studies are required to give more precise and quantitative discussions. Concerning the slope protection work against flooding, a few model tests were carried out to investigate by what material and where and how it should be constructed to get more effective protection. Much discussion is still needed on this subject to apply it for actual design and construction of embankments.