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■ 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(l): <br /> • Decomposition: The deterioration and volume 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 Com 2ression: The compression 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 phase. <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 for settlement <br /> calculations. <br /> 3. FINAL CLOSURE DIFFERENTIAL SETTLEMENT <br /> 3.1 CHANGES IN FINAL CLOSURE GRADES <br /> The primary concern 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-CAl-AA/3110 Austin Road Landfill Expansion August 2,1995 <br /> MEIOBDOC Landfill Settlement Page 2 <br />