Constitutive Models for Municipal Solid Waste in Landfills

The effectiveness and safe operation of a municipal solid waste (MSW) landfill is determined by the hydraulic, mechanical, biological and thermal processes within the waste mass in landfill. The understanding of the behavior of MSW is further exacerbated by the simultaneous coupled interactions between the aforementioned processes. These complex interactions stand as a unique challenge in reliably predicting the overall performance of a landfill system. One of the most intricate issues in numerical modeling of MSW behavior in landfills is the prediction of mechanical response (strength and settlement) of the MSW under different stress states. Realistic representation and accurate prediction of the strength and deformation aspects of MSW is critical for analyzing the instability and integrity within the landfill and its components. In this regard, several researchers have formulated constitutive models to predict the stress-strain behavior of MSW. But these studies do make assumptions that omit some of the important characteristics that are unique to MSW, thus lacking the realistic representation of the MSW behavior in their mathematical formulation. This study presents a critical review of some of the most prominent constitutive models developed for MSW till today. The current research status and a practical approach to simulating the MSW mechanical behavior based on the review of the findings from the published literature is discussed. Finally, the key challenges that need to be addressed in accurate representation of the mechanics of MSW are highlighted.