Embankment Failures and Slope Protection of Earth Dams during Flooding

为研究水库蓄水后库水急剧增加引起土坝渗透破坏的机理，了解在土坝整体破坏过程中，哪些因素是诱发破裂的主要因素，以及破裂发生的时间和方式，进行了土工模型试验。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。通过对几个不同压实条件下的土坝模型进行试验，研究了压实条件对填土中孔隙水压力发展的影响。一种是干燥且压实不良的填充物，其中由于穿过坝体的渗透水流而导致的内部侵蚀（管涌）占主导地位，尽管溢流水最初会因冲沟侵蚀对下游表面造成轻微损害，并导致管涌的触发。另一种情况是在洪水前处于潮湿和/或高度压实状态的填料，其中由于水的溢流而导致的表面沟蚀以恒定速率向上游侧延伸，内部侵蚀较小。模型试验的孔隙水压力测量和有限元分析在一定程度上揭示了这些路堤的破坏机理，但需要进一步的研究，以提供更精确和定量的讨论。针对防洪边坡防护工程，进行了几个模型试验，以探讨用什么材料、在什么地方以及如何建造才能获得更有效的防护。为了将其应用于实际工程的设计和施工中，还需要进行大量的讨论。

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.