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.