Modelling the water diversion of a sustainable cover system under humid climates

Extreme rainfall significantly threatens the safety of the landfill cover system, especially under humid climates. This study aims to provide design recommendations for a sustainable landfill cover system consisting of a low-permeability soil layer underlying a two-layer capillary barrier for humid climates. First, the numerical back-analysis was conducted for verification against a series of flume model tests. Then, a parametric study was performed to investigate the effects of inclination angle, particle size and layer thickness on the lateral diversion length (DL) of the three-layer cover system under the 100-year return period rainfall of humid climates. The results show that the water lateral DL of the cover system can be greatly enhanced by increasing the inclination angle from 3° to 18°. Moreover, the bottom layer of the cover system with a coarser d₁₀ was more susceptible to the impact of the heavy rainfall, while this can be alleviated by increasing the thickness of the bottom layer. A dimensionless number, defined as the ratio of thickness and d₁₀ of the bottom layer, is proposed for designing lateral diversion of the three-layer cover system under humid climates. To preserve the maximum DL, it is suggested that the proposed dimensionless number should be larger than 95 and 110 for the design of rainfall events with 50-year and 100-year return periods for humid climates, respectively.