Reliability-Based Optimization for the Design of Greenland fill Cover Systems Considering Stress-Dependent Hydraulic Properties

Landfill cover systems are crucial for preventing rainwater infiltration into waste. Although the effectiveness of three-layer landfill cover systems using recycled concrete aggregates (RCAs) under extreme weather conditions has been validated, there is limited research on optimizing their design. Furthermore, vegetation is a vital component of landfill covers, enhancing aesthetics and eco-friendliness while improving system performance.However, factors such as spatial variability in cover material properties and root characteristics are generally ignored. The impact of thickness-induced stress on hydraulic properties is also typically neglected, even though stress effects can significantly affecthydraulic properties. Therefore, this study aims to provide reliability-based optimization design recommendations for vegetated three-layer landfill coverswith RCAs by considering these factors simultaneously. Stress effects are captured using a stress-dependent soil-water retention curve (SDSWRC), with hysteresis considered. Uncertainties in soil void ratio (e_b) and root volume ratio (R_v) within the root zone are characterized by copula-based cross-correlated random fields, while uncertaintiesin the bare zone are depicted by eb random fields. The spatial variability of the SDSWRC and the water permeability function are further characterized based on empirical equations. Subsequently, the effects of planting strategy on the failure probability of the landfill cover system are analyzed. Correspondingly,reliability-based optimization recommendations for vegetated landfill covers, focusing on vegetation planting strategy, are provided.

Keywords: Landfill cover, Stress-dependent hydraulic properties, Vegetation, Copula theory, Random finite element method, Optimization design.