Comparison of waste settlement characteristics for two landfills disposed in long sequential periods

Changes in waste management policy affect the settlement characteristics of waste landfills in which the waste disposal is operated for decades. In this study, the waste settlements were calculated by using the data measured in two multi-staged landfills for 27 years. The relationship between the changes in waste management policies and settlement characteristics is analyzed. Sequentially launched waste management policies reduced the organic matters in municipal solid waste (MSW) of the landfill. This change in turn influenced the engineering properties of landfill waste, e.g. water content, unit weight, and initial void ratio, etc. Due to the reduction of food waste in landfills, the water content decreased and the unit weight increased. The initial void ratio declined by the decrease of water content and the increase of unit weight. The annual primary and secondary compression indices, C_c and C_α, of each lift also increased/decreased due to the change in waste composition. The C_c of Phase #1 increased from an average of 0.34 to an average of 0.51 because the percentage of coal ash in MSW drastically decreased and the percentage of food, paper, and plastic, which are highly compressible, increased. On the other hand, the C_c of Phase #2 declined from an average of 0.15 to an average of 0.025 due to the decrease of the waste compressibility from the reduction of organic matters. The C_α of Phase #1 and #2 decreased by the reduction of organic matter and moisture which are needed for biodegradation of wastes in the landfill.