Towards a fundamental model to predict the settlements in bioreactor landfills

Settlement prediction is one of the main concerns in design and maintenance of a bioreactor landfill. Accurate prediction is essential for design of piping systems used for the delivery of re-circulated leachate and collection of gases. Though the major component of settlement is due to the decomposition of municipal solid waste over several years, considerable amount of settlement takes place during the initial construction stage too, which is usually unnoticeable as it happens during construction. A comprehensive model for settlement analysis of a bioreactor landfill should be able to demonstrate not only the settlements due to biodegradation but also the settlements that occur due to mechanical compression during initial construction stage. Often an overall compressibility index is defined similar to that of clays, to explain compressibility of waste, but not much attention has been paid to the settlement behavior during the initial stage or during construction. This manuscript describes a procedure to compute settlements due to mechanical reasons in a bioreactor landfill by separating that from the biodegradation. Then a new conceptual framework was proposed to numerically predict the settlements using time dependent waste properties and landfill geometry.