Abstract
A newly developed and validated constitutive model that accounts for primary compression and time-dependent mechanical creep and biodegradation is used for parametric study to investigate the effects of model parameters on the predicted settlement of municipal solid waste (MSW) with time. The model enables the prediction of stress strain response and yield surfaces for three components of settlement: primary compression, mechanical creep, and biodegradation. The MSW parameters investigated include compression index, coefficient of earth pressure at-rest, overconsolidation ratio, and biodegradation parameters of MSW. A comparison of the predicted settlements for typical MSW landfill conditions showed significant differences in time-settlement response depending on the selected model input parameters. The effect of lift thickness of MSW on predicted settlement is also investigated. Overall, the study shows that the variation in the model parameters can lead to significantly different results; therefore, the model parameter values should be carefully selected to predict landfill settlements accurately. It is shown that the proposed model captures the time settlement response which is in general agreement with the results obtained from the other two reported models having similar features.
Highlights
Prediction of municipal solid waste (MSW) landfill settlement is required to assess the integrity of cover systems and appurtenant systems, estimate the landfill airspace, and design the end-use facilities
MSW settlement is mainly attributed to: (1) physical and mechanical processes that include the reorientation of particles, movement of the fine materials into larger voids, and collapse of void spaces; (2) chemical processes that include corrosion, combustion and oxidation; (3) dissolution processes that consist of dissolving soluble substances by percolating liquids and forming leachate; and (4) biological decomposition of organics with time depending on humidity and the amount of organics present in the waste
It can be noted that the primary compression constitutes 63.7%, creep contributes to additional 8.2 % and the biodegradation contributes to 28.1% for the ultimate settlement based on the model of Marques (2001)
Summary
Prediction of municipal solid waste (MSW) landfill settlement is required to assess the integrity of cover systems and appurtenant systems (gas and leachate collection pipes), estimate the landfill airspace, and design the end-use facilities (e.g., golf course, industrial/commercial building). Several models have been reported in the literature to predict settlement of landfills (Park and Lee, 1997, Machado et al 2002, Marques et al 2003, Machado et al 2008). Park and Lee (1997) proposed a settlement model that considers time-dependent biodegradation of waste. Marques et al (2003) presented a model to obtain the compression of MSW in terms of primary compression in response to applied load, secondary mechanical creep, and time-dependent biological decomposition. It was observed that a single set of parameter values can provide reasonably good representation of all the waste in the vicinity of the test fill and recommendations for applying the model to other landfills are provided. The predictions of stress strain response from the model and observations from the experiments were compared and guidelines for the use of the model are suggested
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