Comparative assessment of settlement models for municipal solid waste landfill applications

The biodegradation of organic matter in municipal solid waste (MSW) landfills increases the void ratio and weakens the structural strength of the refuse within a landfill leading to a substantial loss of volume and settlement. Development of completed landfill sites, which has become highly desirable particularly in land-limited locations, is invariably hindered by this settlement. Estimating longterm landfill settlements becomes an integral part of the plans for the final closure of a site and its ultimate reuse. The rate and magnitude of landfill settlement depend primarily on refuse composition and operational management practices which affect biodegradation and stabilization processes within landfills. Field scale experiments were conducted to measure refuse settlement rates, amongst other parameters, under different operational management practices including leachate recirculation, and addition of water, pH buffer and microbial seed. The effect of these practices on settlement rates and magnitude is evaluated. Field test data are used to calibrate mathematical models that are traditionally used in soil consolidation. The model parameters obtained can be used as guidance in simulating landfill settlement rates and correlating these rates to refuse biodegradation and stabilization processes within landfills.