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3-7 ® final slopes under both static and dynamic conditions. A copy of the slope stability analysis has been included in Appendix E. To evaluate the static stability of the proposed refuse cover system at various design inclinations and slope heights, the proposed cover configuration was analyzed by typical force equations. For this case, the soil cohesion was neglected. Static refuse cover slope stability (assuming a failure at the cover/MSW interface) for all three slope inclinations analyzed indicates a factor of safety of at least 1.5. To analyze the cover layer itself, the infinite slope method was utilized. This analysis assumes that the failure takes place within the soil cover itself. Two cases were analyzed: unsaturated and fully saturated. Static refuse cover slope stability for the steepest proposed slope inclination of 3.2:1 (horizontal to vertical) indicates an unsaturated factor of safety of 2.31 (typically has to be greater than 1.5) and a saturated factor of safety greater than 1.3 (typically a saturated factor of safety of 1.1 to 1.2 is adequate). The proposed 2:1 (horizontal to vertical) slope below the 15-foot wide benches was analyzed for static and dynamic stability by the use if the computer program SLOPE/W. The results of the static stability analysis indicate a factor of safety of 1.92. The three proposed cover inclinations and heights were analyzed for dynamic displacement. For analysis of the dynamic condition, the cover configuration was iteratively solved for various horizontal ground accelerations for a factor of safety of 1.0. Seismically induced permanent displacement was estimated using procedures described by Bray and Rathje (1998) and Bray et. al. (1998), which account for the failure wedge height, yield acceleration (ky), MHA, shear wave velocity of the waste, the period of the waste, period of the earthquake waves, an empirical non-linear response factor, and the duration of shaking. Based on the site specific earthquake response factors, a Maximum Horizontal Equivalent Acceleration (MHEA) is calculated and compared to the yield acceleration. If the MHEA is greater than the yield acceleration, then earthquake-induced displacement is indicated. If the yield acceleration is greater than the MHEA, then earthquake-induced displacement is not likely to occur. The ky value was then used to estimate dynamic displacement of the cover under dynamic conditions using the Bray and Rathje (1998) method, as necessary. The results of the analysis indicate that the calculated dynamic displacement of the landfill cover in less than one inch. The calculated displacement is significantly less than the 6 to 12 inches generally considered to be the maximum movement that a landfill cover system can accommodate without compromising the integrity of a landfill's environmental control systems (Seed and Bonaparte, 1992). The dynamic stability of the 2:1 slope below the proposed benches was also evaluated. To evaluate the dynamic response to the MHA event, a pseudo-static analysis was performed to solve for the horizontal site acceleration that would cause a factor of safety of 1.0. The acceleration was 0.34g. The slope was then analyzed for permanent dynamic displacement in accordance with the procedures described above by Bray and Rathje (1998) and Bray et. al. (1998). No dynamic displacement was calculated for this slope. In summary, the seismic stability analyses indicate that the earth-induced displacement of the landfill cover and 2:1 slope below the proposed 15-foot wide bench will be negligible under MCE loads. Forward Landfill Stage 16 Partial Final Closure/Post-Closure Maintenance Plan-June 2011 SWT Engineering z:\projects\allied waste\forward\11-1014 partial fnl clsr pin\partial final closure plan document\text\sec 3.doc