Field test on seepage performance of soil cover with different types of vegetation

The aim of study is to investigate anti-seepage performance of landfill covers with different types of vegetation. First, three field test sites were built with different types of vegetation conditions, i.e. no vegetation, Bermuda grass (fibrous root) and vetiver grass (tap root). During one year of vegetation growing under the subtropical climate, the real-time responses of volumetric water content (VWC) and matric suction were monitored at different depths of the covers from July to September when the rainfall and evaporation were the largest. Results show that the vetiver grass enhances the coefficient of permeability and reduces the integrity of the cover. The Bermuda grass decreases the coefficient of permeability and improves the performance of the cover. The reason is that the effects of different plant roots on the moisture flow path in cover are different. The monitoring results indicate that the effect of vegetation on the water content changes at 5 cm depth can be ignored. The changes of VWC and matric suction at this depth are mainly controlled by the rainfall and evaporation. The water content at 50 cm depth changes only in cover with vetiver grass. This indicates that the vetiver grass results in preferential flow in deep soils. The Bermuda grass mainly changes the moisture flow within small depth.