THESIS
2019
xiii, 141 pages : illustrations ; 30 cm
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...[
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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.
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