Reliability assessment of field performance of in-service landfill cover systems under humid climates

Landfill cover systems face various uncertainties throughout their service life. Previous studies have typically analysed their performance deterministically, focusing on limited time frames. This study investigated the effectiveness of landfill covers over a 100 year service life using reliability-based approaches. Uncertainties related to in-service three-layer landfill covers in Shenzhen, including material properties, plant characteristics and rainfall features, were quantified. A numerical model was validated through field-monitored atmospheric and percolation data. Numerical parametric studies were then conducted to predict the probability of failure (p_f) over a 100 year service life. The measured maximum annual percolation for a cover using recycled concrete aggregates (RCAs) was 22·3 mm (40 months of monitoring), approximately 16% and 11% lower than for non-vegetated (26·6 mm) and vegetated (25·0 mm) covers using natural soils (90 months of monitoring). Although planting vegetation decreases p_f of a cover using natural soils by at least 43% compared to a non-vegetated cover, reducing the saturated permeability (k_s) of the bottom layer is more effective. This is because the bottom layer of a cover using RCAs had only 17% of the value of k_s for a cover using natural soils, resulting in a p_f value three orders of magnitude lower. Despite this, the three-layer landfill covers using different materials possess a service life that exceeds 100 years.