Field Study On The Interaction Of Vegetation-clay-water In Final Cover

At present, sanitary landfill is the main method to deal with municipal solid waste. The top cover layer of the modern sanitary landfill is located at the top of the landfill site, which is like the "skin" of the whole landfill site, which can prevent the infiltration of rainwater from the outside world.Vegetation is an important method for the ecological restoration of the landfill cover. However, the effect of vegetation on the leakage resistance is still controversial, and the key variable of the cover layer is the vegetation type and cover layer thickness. The growth of plant roots in the clay layer will form a certain dominant flow channel, increase the permeability of the overburden layer, and its root system can reduce the clay layer in dry wet cycle, freezing and thawing cycle, and this positive and negative interaction needs further research. The research content of this paper is to study the effect of vegetation cover on the impervious performance of the plant in the vegetation layer.In this article, the field test was used to research the mechanism. First of all, three cover layer models-the cover layer without vegetation, the cover layer with bermudagrass coverage(fibrous root system of vegetation), the cover layer with vetiver grass mulch(taproot system of vegetation)- are established in the natural environment. By comparison of the data of the same depth and the data of the same cover layer, we draw the following conclusions: the effect of vegetation on 5 cm depth can be ignored, the change of water content on this depth is mainly affected by the weather; on 50 cm depth the cover layer with vetiver grass mulch is affected by the weather, and others are not affected; under the action of rainfall of high strength, the penetration rate of cover layer with vetiver grass mulch is the fastest; in the evaporation of high intensity, the transpiration of cover layer with vetiver grass mulch is also the greatest.While in the rainfall and evaporation during moderate intensity, the diffenrence is not obvious; the transient method is used to calculate the permeability coefficient of three kinds of cover layer on 15 cm depth, in which the permeability of vetiver grass mulch layer is larger, and the difference between cover with bermudagrass coverage and cover without vegetation is not large; by the calculation of changes on water storage in cover we analyse the evapotranspiration intensity of the three kinds of cover, and find that the evapotranspiration intensity of cover layer with vetiver grass mulch is the largest, while the evapotranspiration intensity of cover layer with bermudagrass coverage is the least.Based on the experiment,this paper evaluate the long-term service performance of the three kinds of cover layer by numerical simulation. Firstly, we get the the numerical simulation results which are obtained on the 5 cm, 15 cm and 50 cm depth, and verify the reliability of numerical modeling by a comparative analysis of the value of the test monitoring and the numerical simulation results. Then the paper evaluate the long-term service performance by calculating the annual leakage of the three kinds of cover under a year of climate boundary conditions. At last, this paper calculate the requirement to get a satisfactory result in which the leakage is less than 5 mm/y while three cover layers working independently. The results are as follows: the thickness of cover with bermudagrass coverage is 135 cm, the thickness of cover without vegetation is 145 cm, and the thickness of cover with vetiver grass mulch is 165 cm.