Water infiltration into a sustainable three-layer landfill cover system using recycled concrete aggregates

Abstract

Recently, a great deal of construction and demolition (C&D) wastes have been produced due to the fast urbanization in China. Landfilling is a simple and cost-effective method to dispose of municipal solid waste. A permanent cover is necessary to reduce water infiltration and percolation. The construction of landfill cover always needs a large quantity of natural soil, especially clay, which is often locally not available. In this study, a sustainable three-layer landfill cover built by recycled concrete aggregates is proposed. To be specific, from bottom to the top, the three-layer cover system consists of a 300-mm-thick layer of completely decomposed volcanic rocks (CDV), a 200-mm-thick layer of coarse recycled concrete aggregate (CRC) and a 400-mm-thick layer of fine recycled concrete aggregate (FRC). Fine and coarse recycled concrete aggregates are used to form capillary barrier (CCBE). The low-permeability waste soil (i.e. CDV) layer is added underneath the CCBE to prevent percolation after any breakthrough of CCBE. The objectives of this study are to investigate the effectiveness of the sustainable three-layer landfill cover system built by recycled construction waste in preventing percolation and to compare the effects of plant types on water infiltration in this type of cover system. One-dimensional column infiltration and two-dimensional flume model tests were carried out. From the one-dimensional column tests, after drying for 60 days, higher suction and lower VWC in each layer in planted one-dimensional soil columns were observed, which indicates the plants are indeed pulling more water than the bare soil as expected. Evapotranspiration (ET) effects: shrub > grass > bare. This is because shrub has deeper root and larger influence zone of root water uptake than grass species. After ponding, suction maintained below the root zone in the two vegetated covers was higher than that of the bare cover, revealing the presence of vegetation significantly enhances the effectiveness of the sustainable three-layer landfill cover system in preventing water infiltration. Compared with grassed cover, vegetated cover with shrub can maintain a lower VWC and hence induce a higher suction in the layers even after 48-h ponding, which is equivalent to more than 1000-year return period rainfall. This suggests that shrub was more effective in reducing water infiltration in three-layer landfill covers at humid climates. From the two-dimensional flume tests, the results show that the breakthrough in the two upper layers (CCBE) built by fine and coarse recycled concrete aggregates occurred after extreme rainfall (i.e. 5-year return period rainfall). During a 100-year return period rainfall (for example rainfall intensity: 36.5 mm/h, rainfall duration: 12 hours), most of rainfall becomes surface run-off (more than 75%), and water infiltrated into soils was mainly drained by CRC layer. There was no percolation in the bottom layer, which indicates that the three-layer cover system with recycled concrete is a promising sustainable alternative landfill cover system for humid climates. With the increasing of slope angle, surface run-off increases, water infiltrated into cover soil decreases, and the breakthrough time increases.

Date of Award	2019
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology