Comparative analysis of two evapotranspiration landfill covers incorporating long-term environmental effects on soil permeability

Long-term environmental effects elevate soil permeability in evapotranspiration covers, thereby altering their hydrological behavior. We established a numerical model to simulate the two-dimensional hydrological behavior of these covers, incorporating depth-dependent exponential permeability functions to represent long-term environmental effects. The verified model was then used to evaluate the hydraulic performance (specifically percolation control) and slope stability of both monolithic soil covers (MSCs) and capillary barrier covers (CBCs) under identical meteorological conditions. Five levels of permeability increase were tested for each cover. Results showed that CBCs performed better than MSCs under increased permeability, maintaining superior percolation control and slope stability. While MSCs exhibited deteriorating percolation control with rising permeability, CBCs effectively minimized percolation across all scenarios. Furthermore, stability analysis identified the critical slip surface as the basal interface for MSCs and the fine-coarse soil interface for CBCs. Increased permeability significantly reduced the factor of safety for MSCs, yet had negligible adverse effects on CBC stability. MSC designs based solely on initial permeability parameters would underestimate long-term percolation and instability risks, whereas CBC designs could maintain functional integrity with initial permeability parameters. These findings demonstrate the superior reliability of CBCs relative to MSCs as alternatives to conventional cover systems.