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�7 <br />C <br />GeoSyntec Consultants <br />Table 3-2 <br />Assumed Material Properties <br />Final Cover Slope Stability Analyses <br />WMU B, Forward Landfill <br />Notes: 1) The assumed shear strength parameters are based on a normal stress range of 100 to 300 <br />pounds per square foot (psf) (5 to 15 kPa) at large shear displacement. <br />2) NA — Not applicable <br />The seismic slope stability was analyzed by including an inertial <br />(i.e., pseudo -static) horizontal acceleration or seismic coefficient (ks), measured as a <br />percentage of gravity. The design earthquake was established as a Richter <br />magnitude 7.0 event characterized by a maximum peak bedrock acceleration of 0.18g <br />[CH2M HILL, 19941 for the maximum credible earthquake (MCE). Following the <br />procedures outlined in Subtitle D seismic design guidance for MSW landfills <br />[US EPA, 1995], the bedrock acceleration was amplified to 0.28g at the top of the <br />landfill due to the site specific effects of stiff soils and the waste mass. Thus, the <br />effective peak horizontal acceleration of the final cover system was assumed to be <br />kmax = 0.288. The seismic stability analysis was performed to establish the "yield <br />acceleration" (ky) resulting in a factor of safety of 1.0. The ratio of ky to kmax was <br />plotted against the design magnitude earthquake to estimate permanent seismic <br />J:\ALLIED\FORWARD\CLOSUREPLAN\REPORT 3-11 99.11.30 <br />Univ <br />Shear Strength <br />Weight <br />Source <br />Cohesion <br />Friction <br />Material <br />(pcf) <br />(psf) <br />Angle <br />of Data <br />Vegetative Layer (silty sand <br />Duncan et al. [ 1989] <br />[SM] or clayey sand [SC]) <br />120 <br />10 <br />34° <br />Vegetative <br />GeoSyntec [1998] <br />Layer/Geocomposite Drainage <br />NA <br />25 <br />270 <br />Layer interface <br />Geocomposite Drainage <br />GeoSyntec [1998] <br />Layer/Compacted Clay <br />NA <br />25 <br />270 <br />interface <br />Compacted Clay Liner (Lean <br />Duncan et al. [ 1989] <br />Clay [CL]) <br />120 <br />100 <br />280 <br />Notes: 1) The assumed shear strength parameters are based on a normal stress range of 100 to 300 <br />pounds per square foot (psf) (5 to 15 kPa) at large shear displacement. <br />2) NA — Not applicable <br />The seismic slope stability was analyzed by including an inertial <br />(i.e., pseudo -static) horizontal acceleration or seismic coefficient (ks), measured as a <br />percentage of gravity. The design earthquake was established as a Richter <br />magnitude 7.0 event characterized by a maximum peak bedrock acceleration of 0.18g <br />[CH2M HILL, 19941 for the maximum credible earthquake (MCE). Following the <br />procedures outlined in Subtitle D seismic design guidance for MSW landfills <br />[US EPA, 1995], the bedrock acceleration was amplified to 0.28g at the top of the <br />landfill due to the site specific effects of stiff soils and the waste mass. Thus, the <br />effective peak horizontal acceleration of the final cover system was assumed to be <br />kmax = 0.288. The seismic stability analysis was performed to establish the "yield <br />acceleration" (ky) resulting in a factor of safety of 1.0. The ratio of ky to kmax was <br />plotted against the design magnitude earthquake to estimate permanent seismic <br />J:\ALLIED\FORWARD\CLOSUREPLAN\REPORT 3-11 99.11.30 <br />