Embankment Failures and Slope Protection of Earth Dams during Flooding

摘要为研究洪涝期水库水量快速增加引起的土坝渗流破坏机理，进行了离心模型试验，了解哪一因素是引发土坝破裂的主要因素，以及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流破坏的可行性是今后土石坝水力压裂研究的另一个重要课题。对不同压实条件下的几种土坝模型进行了试验，研究了不同压实条件对填方孔隙水压力发展的影响。洪水期间水库水量的快速增加引起的堤防破坏有两种不同的模式。一种是在干燥和压实度差的填方中，由于渗水流经坝体而导致的内部侵蚀（管道）占主导地位，尽管溢流水最初会通过沟槽侵蚀对下游表面造成一点损害，并有助于触发管道。另一种是在洪水前填方处于湿润和/或高度压实状态时，由于水的溢流，地表沟槽侵蚀以恒定的速率向上游延伸，内部侵蚀很小。孔隙水压力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制，但需要进一步的研究来给出更精确和定量的讨论。针对防汛护坡工程，进行了一些模型试验，探讨采用什么材料、在什么地方以及如何施工才能获得更有效的防护。在实际的路堤设计和施工中，还需要对这一问题进行大量的讨论。

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.