EFFECTS OF PLANT GROWTH ON WATER INFILTRATION INTO THREE-LAYER LANDFILL COVER SYSTEM

Plant has been widely recognized for improving the sustainable performance of geotechnical infrastructures. However, the influences of plant growth on water infiltration into layered landfill cover are still unclear. This study aims to quantify the effects of plant growth on the variations of soil hydraulic properties and water infiltration into a three-layer landfill cover using recycled concrete without geomembrane under humid climates. Full-scale field monitoring was carried out for two years at the Shenzhen Xiaping landfill. Numerical analyses and parametric study were also conducted. The field monitoring results show that saturated water permeability(k_s) decreased linearly with the increase of root length density(RLD). Compared with bare soil, the reductions in k_s and infiltration rate due to the rise of RLD were up to 55%, 18% and 35%,respectively. Consequently, higher matric suctions were preserved in the grassed three-layer landfill cover system compared to the bare one during the field monitoring, which are also support by the numerical results. However, no significant difference in matric suction was observed between the bare and grassed covers under the 100-year return period rainfall. During the two-year monitoring, the occurrence of grass roots resulted in a reduction in cumulative percolation by 21%. They all meet the USEPA recommended criterion of 30 mm ·a^-1. The field monitoring results demonstrate the effectiveness of bare and grassed three-layer cover systems using construction waste without geomembrane in humid climate areas.