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2.3.3 Supported Lining Systems for Slopes Flatter than 6:1 <br /> The grade in the portion of the landfill that connects the northern and southern portions of WMU FU- <br /> 08 is approximately ten percent or less. Because this region overlies the former Austin Road Landfill <br /> and is relatively flat, a geogrid will be placed to support the overlying liners and LCRS. <br /> The geogrid calculations are based on both the short-term tensile strength of the geogrid and the long <br /> term allowable tensile strength. Because the multiaxial yield strength of geomembranes is about 7 to <br /> 10 percent, the specified short term tensile strength of the geogrid is measured at five percent rather <br /> than using the ultimate geogrid tensile strength. This requirement maintains strain compatibility by <br /> allowing the geogrid to achieve the required tensile strength before the overlying geomembrane <br /> deforms beyond its yield strength. <br /> Because the tensile strength of geogrids can degrade over time due to factors such as creep <br /> installation damage, and other environmental factors,the short-term tensile strength of the geogrid is <br /> reduced to calculate a suitable long-term allowable load. The long-term allowable load is compared <br /> to the required tensile load in specifying the geogrid properties. <br /> The final lifts of refuse on the top deck of the former Austin Road Landfill were placed in 2002. <br /> According to site operations personnel, no large metal objects such as refrigerators were placed in the <br /> final refuse lifts. The type of refuse placed was municipal solid waste and some construction and <br /> demolition debris. It was estimated that the largest void that may collapse in this type of waste has a <br /> diameter of approximately 4-ft. Based on the potential that a void of this diameter may collapse <br /> directly under the interface lining system,the tensile requirement for the geogrid was calculated to be <br /> approximately 550 lbs/ft(Appendix B). <br /> 2.4 Refuse Fill Grades <br /> Final waste grading plans are not included in this report. This information is available in the <br /> Preliminary Closure and Postclosure Maintenance Plan (BAS, 2002). The maximum waste fill slope <br /> during the filling of WMU FU-08 will be approximately 3:1, as presented in the slope stability <br /> analysis in Appendix B and discussed in Section 3 of this report. <br /> WMU FU-08 2-4 <br />