This article has studied the role of clay overburden layer in prevention of contamination from seepage of wastewater ditch to underground water with a analogy method ,and in order to prevent contamination of seepage wastewater, the study defermined the critical thickness of clay overburd layer.

Through imitative experiment research on lead removal of contaminated rivers and ditches by three kinds of media of unsaturated zone,it is found that lead in contaminated rivers and ditches can be removed and depurated by different media, and removal ratio of lead increases with depth Different media have different removal results:medium sand have a higher removal ratio than coarse sand.

The article sets forth the selection of the design scheme of the open drainage channel to underpass the expressway, the tunnel design and construction step flow as well as the construction monitoring methods.