江河大堤双层地基渗透破坏机理模型试验研究

Failure mechanism of seepage in levees with double-layer foundation

本文通过模型试验研究了双层地基的渗透破坏问题。在模型设计中不仅考虑下层地基中承压水头的大小,而且考虑土的渗透稳定性,并以下层出现的承压水头大小按两土层渗透系数比值,将其细分为4种地层结构,分别研究其渗透破坏机理。试验结果表明,渗透破坏都是开始于上层土,上下两种土层渗透系数之比大于100的地层为最危险结构,最终控制地基渗流稳定的是下层管涌型土层。整个破坏过程可描写为上层流土穿孔—下层管涌—上层流土破坏向堤脚发展—上层整体破坏。下层管涌型土的允许水力比降应采用水平允许水力比降,以此确定双层地基不允许的渗透破坏范围。

Model test for seepage failure in levees with double-layer foundation was carried out. In the experiment not only the water pressure but also the stability of soil seepage was considered. The foundation structures in existing levees of rivers in China are classified into 4 kinds according to the confined water head of lower layer and the ratio of seepage coefficient between two layers. The experimental result shows that the seepage failure always begins in upper layer soil, plays the important role in controlling the stability of seepage. The foundation with the ratio between two layers of soil higher than 100 is the most dangerous structure. The failure can be described as penetration initiated in the upper layer-piping occurred but the lower layer seepage coefficient process of seepage to the lower layer- failure of upper layer developed to the toe of levee-complete failure of upper layer. It is proposed that the limit of allowable seepage erosion in dual-layer foundation is determined by the horizontal allowable hydraulic gradient in the lower layer.