双层堤基管涌发生发展的试验模拟与分析

Laboratory tests and analysis on piping in two-stratum dike foundation

利用室内试验模拟了双层堤基管涌的发生及发展过程。通过分析水头分布、流量、以及出砂量等的变化,将破坏的发生及发展归结为4个阶段:上覆层破坏前的稳定阶段、上覆层破坏阶段、上覆层破坏后的稳定阶段、整体破坏阶段。研究发现,在上覆层破坏前,上覆层承担了大部分的水头差,当上覆层破坏后,这部分水头差转由下伏砂层承担,造成下伏层水力梯度的升高,如果水力梯度超过了下伏层的临界水力梯度,则下伏层发生渗透破坏。一次渗透破坏发生后,降下上游水头,重复增加水头的过程,模拟地层在多次渗透破坏作用下,地层抵抗渗透破坏能力的变化。发现一旦渗透破坏发生后,地层再次抵御渗透破坏的能力急剧下降,多次破坏后,试样内形成贯穿上、下游的集中渗漏通道,且通道规模随着试验次数的增加而增长,若不及时采取有效措施,当通道规模发展到一定程度后,通道上部会发生塌落而使堤坝产生溃口,进而使堤坝溃决。

The piping erosion phenomena are simulated in laboratory tests.The erosion is divided into 4 periods through the analysis of hydraulic head,flux and spring sand quantity：steady period before the superstratum breaking,period of the superstratum breaking,steady period after the superstratums breaking and period of the entire breaking.It is found that at the very beginning the superstratum bears the most of the head difference,which shifts to the underlying stratum after the superstratum breaking.Then the hydraulic gradient in the underlying stratum is enhanced greatly for the head difference shifting.And if the hydraulic gradient exceeds the critical value,the piping erosion will happen in the stratum.After a period of erosion,the upper hydraulic head is reduced and raised again for the next period of tests to simulate seepage erosion in breaking dike foundation.After some repeated tests,the capability of the dike foundation to resist the seepage erosion is deeply reduced and a concentrated leakage passage occurs in the underlying stratum.The foundation may burst for the development of the leakage passage if no effective measure is taken.