Experimental study on overtopping breaching of noncohesive homogeneous embankment dams
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摘要: 针对当前土石坝溃决机理试验研究中泥沙粒径取值偏小、各砂样粒径相差不大的现状,采用粒径对比明显的两组砂样进行了土石坝漫顶溃决试验.试验表明,在给定的较强的初始冲刷条件下,粗细两种颗粒坝体的溃决过程基本一致,均是以水流的下切侵蚀为主,在坝顶下缘位置有溯源冲刷现象出现.整个溃决过程可明显分为3个阶段,第1阶段为坝顶下缘处陡坎形成阶段;第2阶段为陡坎坍塌,冲刷加剧阶段;第3阶段为出现逆行沙垄的冲刷终止阶段.试验还发现,下游坝坡对溃决过程的影响比较显著,坝坡越陡,坝顶侵蚀速率越快,洪峰值越大.另外,由于粗颗粒抗冲刷性强,同等条件下粗颗粒坝体溃决洪水过程偏矮胖,洪峰值偏小,但是值得注意的是,相比于较大的颗粒粒径差距而言,其洪峰值的差异并不是太大.Abstract: Most experimental studies on overtopping breaching of embankment dams use small-sized sediment grains and little differences in the diameter profile of sand specimens.Aiming at the issues of sediment sizes,two distinct types of sediments are used in this experimental study.The experiment reveals that the breaching processes of two types of dams are basically identical under relatively strong erosion conditions.During the overtopping event,the down cutting phenomena are most likely observed and the backward erosion phenomena occur only near the crest of the dam.The entire breaching process can be divided into three stages.In the first stage,a headcut is formed near the lower margin of the dam crest.In the second stage,the headcut collapses and the erosion actions become violent.In the third stage,antidunes occur and the erosion actions terminate.Experiments also detect that the downstream slop of the dam has a significant effect on the breaching process.The steeper the slope is,the faster the degradation rate of the crest is and the larger the flood peak discharge is.Moreover,a flat hydrograph is produced by the embankment dam-breach flood,which contains coarse sand particles.The corresponding value of the flood peak tends to be smaller compared to that of resulting from small-sized materials.However,it is worth mentioning that a large difference in sediment sizes will have a limited effect on the peak discharge.
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Key words:
- Embankment dam /
- flume experiment /
- overtopping /
- breaching process
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