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1,200 feet per second when modeling varying refuse fill heights above the soil. The shear-wave velocity of the stiff soil/bedrock was assumed to be 3,000 feet per second. The variations of shear modulus and damping ratios with strain for sand are based on Vucetic and Dobry (1991) for a material having a plasticity index of zero. 3.3.2 Results of Slope Stability Analyses A discussion of the results of the slope stability analyses performed for the critical condition is presented below. SLOPEW output data and plots are presented in Appendix B. Static Stability As shown on the Construction Drawings (Appendix A), WMU FU-03 is directly south of the former Austin Road Landfill and directly east of the WMU F-03 leachate impoundment and desilting pond. The southern boundary is offset from the southern property line by approximately 50-feet. The site development plan(BAS,2001) includes development of future modules to the east of WMU FU-03. The slope stability analysis was performed for a maximum Forward Landfill refuse fill elevation of 170-ft with a 3:1 final slope and 20 ft wide benches every 50 vertical feet (effective slope 3.25:1) on the southern side. The critical slope configuration is in the north-south direction. Other sections were considered but assessed to be less critical. As indicated in Appendix B, a minimum factor of safety of 1.8 is obtained for a sliding block shear surface along the base liner and through the refuse in the north-south direction for the effective 3.25:1 final slope. A surface extending along the base liner and side slope interface liner was also analyzed but found to be less critical. A factory of safety of 1.8 is acceptable for permanent slopes. The maximum refuse fill height and slope for WMU FU-03 should be re-evaluated based on actual CQA direct shear tests results on the base and slope liner interfaces. Seismic Response Analysis The SHAKE computer program was used to predict the response of the landfill to the input base rock motions. To model the dynamic response of the critical east-west cross section, the following columns were used: • 80-feet of soil overlying stiff soils/bedrock. This column was used to calibrate the shear wave velocities assumed for the soil. After the results at ground surface were considered to be reasonable,the refuse was modeled above the soils for the remaining analysis. • 70 and 140 feet of refuse overlying 80 feet of soil overlying stiff soils/bedrock. The accelerations at the ground surface for the soil-only column varied between 0.14g(for Mw 7.9 time history)and 0.21 g(for Mw 6.7 time histories). The accelerations at the ground surface for the refuse-soil column varied between 0.14g and 0.15g(for Mw 79 time history)and between 0.20g and 0.30g(for Mw 6.7 time histories). The ground accelerations at the top of the soil-refuse columns were equated to 0,,,a, in the Makdisi and Seed (1977) procedure to estimate deformations. The yield acceleration for the critical section is 0.16g. Based on the results of this analysis (see Appendix B),the magnitude of permanent deformation of the slope was estimated to be less than one foot during a MCE seismic loading event. As discussed in Section 3.2, while it is difficult to assess what deformation would damage a composite base lining system,the current practice is to limit deformations to less than 12 inches(Sharma and Lewis, 1994).The estimated magnitude of permanent deformation can therefore be considered acceptable. FORWARD LANDFILL WMU F-03 AND F-WEST DESIGN REPORT 3-6