Analysis of a landfill cover without geomembrane using varied particle sizes of recycled concrete

Previous studies have demonstrated the effectiveness of a novel three-layer landfill cover system constructed with recycled concrete aggregates (RCAs) without geomembrane in both laboratory and field. However, no systematic investigation has been carried out to optimize the combination of the particle sizes for fine-grained RCAs (FRC) and coarse-grained RCAs (CRC) that can be used for the three-layer landfill cover system. The aim of this paper is to assist engineers in designing the three-layer landfill cover system under a rainfall of 100-year return period in humid climate conditions using an easily controlled soil parameter D₁₀ of RCAs. The numerical study reveals that when D₁₀ of FRC increases from 0.05 mm to 0.16 mm, its saturated permeability increases by 10 times. As a result, a larger amount of rainwater infiltrates into the cover system, causing a higher lateral diversion in both the top FRC and middle CRC layers. No further changes in the lateral diversion are observed when the D₁₀ value of FRC is larger than 0.16 mm. Both the particle sizes of FRC and CRC layers are shown to have a minor influence on the percolation under the extreme rainfall event. This implies that the selection of particle sizes for the FRC and CRC layers can be based on the availability of materials. Although it is well known that the bottom layer of the cover system should be constructed with very fine-grained soils if possible, this study provides an upper limit to the particle size that can be used in the bottom layer (D₁₀ not larger than 0.02 mm). With this limit, the three-layer system can still minimize the water percolation to meet the design criterion (30 mm/yr) even under a 100-year return period of rainfall in humid climates.