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5.3.2.2 GROSS STABILITY ANALYSES <br /> The gross stability of the landfill and liner system was assessed using the <br /> maximum slope height and slope gradient for the proposed landfill development <br /> (Figures 1 and 2 of Appendix Q. Because the actual interface strengths of landfill <br /> liner materials will vary with the manufacturers of particular products used, a <br /> parametric analysis was done to develop a range of acceptable strength <br /> parameters (i.e. combination of cohesion and angle of friction) that will provide a <br /> minimum static factor of safety of 1.5. The following range of parameters were <br /> used in the analysis: <br /> Material Angle of Internal Unit Weight Cohesion <br /> Friction (Ib./cu. Ft.) (Ib./sq. Ft.) <br /> (degrees) <br /> Native soils 1 0 to 33 120 to 125 0 to 2300 <br /> Refuse 2 30 80 200 <br /> Textured HDPE/ Non-Woven 4 to 11 NA 0 to 950 <br /> Geotextile Interface 3 <br /> Internal Strength Hydrated 5 NA 400 <br /> GCL 4 <br /> Non-Hydrated GCL (Textured 14 NA 0 <br /> HDPE GCL) (3 <br /> (1) CH2MHill(1992) <br /> (2) Singh and Murphy(1990) <br /> (3) Range of Values Considered Obtainable <br /> (4) Cetco Manufacturer Certification <br /> As determined in CH2MHill`s geotechnical evaluation of the existing Forward <br /> Landfill (1992), the native soils in the area consist of interbedded layers of sand, <br /> silt, and lean clay. The cohesive soils can be characterized as very stiff to hard, <br /> and non-cohesive sands are dense to very dense. The stability conditions of the <br /> native subgrade beneath anticipated refuse loads are considered non- <br /> problematic. Assuming a refuse height of approximately 200 feet above the <br /> subgrade, CH2MHiII calculated that the factor of safety for failure of a lean clay <br /> layer that is 10 feet below the liner grade would be 2.2 to 2.3. <br /> Forward Landfill)TD 5-15 <br /> L:\Allied\2000.193\Reports\JTD-PC PCMP7OZ:Sec-5.0:5/24/02 <br /> Revision 1:07,/16/02 <br />