Settlement in municipal solid waste landfills: II. Mathematical modeling

The biodegradation of organic matter in 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 is highly desirable particularly in land-limited locations, is invariably hindered by these settlements. Estimating long term landfill settlements becomes an integral part towards final site closure and ultimate usage. The rate and magnitude of these settlements 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 under different operational-management practices including leachate recirculation, addition of water, buffer, and microbial seed. The effect of these practices on settlement rates and magnitude is evaluated. The field test data are used to calibrate mathematical models that are traditionally used in soil consolidation. The models can be applied to simulate landfill settlement rates and correlate these rates to refuse biodegradation and stabilization processes within landfills. The present research work is presented in a series of two papers: I. field scale experiments, and II. mathematical modeling of settlement behavior.