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LJ <br />r� <br />u <br />■ Anticipated settlement of the horizontal expansion liner due to subsidence of <br />underlying natural geologic materials. <br />This report should be considered an initial evaluation of these settlement issues and a <br />demonstration of the technical feasibility of the project but does not constitute_a final design <br />analysis for the landfill expansion liner or cover system. The report notes design issues that <br />will require additional analysis or data collection prior to or during the final design of liners <br />and final cover systems. <br />2.0 LANDFILL SETTLEMENT <br />Landfill refuse exhibits significant settlement from mechanical compression due to overburden <br />and volume loss due to structural deterioration due to decomposition. The mechanisms <br />involved in refuse settlement of landfills are typically classified as follows ('). <br />■ Decomposition: The deterioration and v,alume.loss_of waste products by corrosion, <br />oxidation, or biological decay. This is considered the major mechanism for post - <br />closure landfill settlement. <br />■ Mechanical Compression: Ther cession caused by the self -weight of the landfill <br />or imposed loads such as a vertical expansion over an existing landfill. This can be <br />analyzed similar to the consolidation. of organic soils with a primary consolidation <br />phase and a secondary consolidation hase. <br />■ Raveling: Movement of finer particles into larger voids. This is difficult to <br />distinguish this mechanism from the other mechanisms in the field data for <br />settlement and typically is not independently analyzed for landfill settlement. <br />In each of the following analyses, the primary settlement mechanism was identified and <br />technical literature was reviewed to determine reasonable analysis parameters forsettlement <br />calculations. <br />3. FINAL CLOSURE DIFFERENTIAL SETTLEMENT <br />3.1 CHANGES IN FINAL CLOSURE GRADES <br />The primary concent of differential settlement in respect to final closure grades is the loss of <br />drainage grade resulting in ponding conditions. Three types of differential settlement <br />conditions are considered in this analysis: <br />■ Differential settlement due to the varying depth of refuse fill. <br />WW-1811-CAI-AA/3110 Austin Road Landfill Expansion August 2,1995 <br />NE1033.DOC Landfill Settlement page 2 <br />