Settlement due to anaerobic biodegradation from laboratory landfill simulators

Settlement in landfills is caused by a number of mechanisms, including mechanical compression, creep, biodegradation, and raveling. In the field, because all settlementinducing mechanisms are taking place simultaneously, it becomes very difficult to quantify the contribution of each mechanism to the total settlement. Laboratory tests in large-scale simulators allow the separation of each mechanism, the identification of phases in long-term settlement, and the quantification of the contribution of each phase to the settlement behavior. Results from a systematic review of studies available in the literature are presented. Emphasis is given on quantifying the duration, strain and long-term compression ratio of each phase. Three phases are identified in describing the long-term settlement behavior, with the most significant being the active biodegradation phase. Performance of tests under increasing vertical stress reduces the strain and compression ratio of long-term settlement due to the immediate compression associated with the application of the vertical load and the reduction in void ratio and hydraulic conductivity. However the duration of long-term settlement does not appear to be statistically affected by vertical stress.