Long-term field performance of non-vegetated and vegetated three-layer landfill cover systems using construction waste without geomembrane

This paper compares the field performance of non-vegetated and vegetated three-layer landfill cover systems utilising construction waste but without geomembrane at the Shenzhen Xiaping landfill site in humid climates over a monitoring period of 54 months. The top layer of each cover system was constructed using coarse-grained completely decomposed granite (CDG). The middle and bottom layers were compacted with coarse recycled concrete (CRC) and fine-grained CDG, respectively. Numerical analyses were also carried out. During the 54-month monitoring period, the cumulative rainfall recorded was 9800 mm. Retained pore water pressure in the vegetated cover was close to that in the non-vegetated cover after the heaviest rainfall recorded in Shenzhen during the monitoring period. The pore water pressure retained in the vegetated cover can be higher than that in the non-vegetated cover due to the increased saturated water permeability (k_s) induced by plant growth over 3 years. Surface runoff and water storage capacity in the vegetated cover were about five times and 9% higher than those in the non-vegetated cover, respectively. However, the long-term behaviour of the cover system in respect of these two aspects was influenced by the increase of k_s due to the growth of grass roots. The middle CRC layer diverted infiltrated water by up to 51% of total rainfall. The measured average annual percolation of the non-vegetated and vegetated covers was about 23 mm and 21 mm, respectively. The measured data are supported by numerical analyses and they meet the US recommended criterion.