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BRAY, RATHJE, AUGELLO AND MERRY D Seismic Design for Lined Solid-Waste Landfills 227GEOSYNTHETICS INTERNATIONAL S 1998, VOL. 5, NOS. 1-2 Cover sliding . Analyze the landfill for localized cover sliding near the crest for the design earthquake. Slope stability analyses indicate that the yield acceleration coeffi- cient for localized cover sliding is 0.16. 1. Calculate the seismic loading,MHEACover : MHA Rock 0.33g,NRF 1.05, and T sTm 1.3 from previous analysis MHA Top[(MHARock)(NRF)] 0.9 to 1.1 (50% / 60%) (Figure 8 ) MHA Top (0.33g)(1.05)(0.9 to 1.1) 0.31g to 0.38g MHEA Cover (1.25)(0.31 to 0.38g) 0.39g to 0.48g 2. Estimate the seismically induced permanent displacements: k max MHEA Coverg 0.39 to 0.48, and k y 0.16 (given), so k yk max 0.33 to 0.41 U 100 to 500 mm (from Figure 12, using 50 and 16% exceedance for Mw 7) 4 CONCLUSIONS Landfill performance during recent earthquakes has been generally satisfactory. However, one geosynthetic-lined landfill experienced significant damage, with two tears observed in the HDPE geomembrane liner, and two unlined landfills were dam- aged due to liquefaction-induced lateral spreading. Several landfills have experienced moderate damage, evidenced by cracking in the interim soil cover at waste/natural ground interfaces, cracking and limited downslope movement in cover soils, breaking of gas extraction header lines, and a loss of power to the gas collection system. Back- analyses of landfill performance during the Northridge earthquake in California have provided exceptional opportunities to estimate the dynamic properties of solid-waste fill and geosynthetic interfaces. However, due to the importance of evaluating these properties, additional work is warranted. Results from equivalent-linear and fully nonlinear seismic site response analyses in- dicate that the dynamic response ofa MSWLFcan vary significantly due to reasonable variations ofdynamic waste properties, fill heights, site conditions, and input rock mo- tions. However, forthe base sliding case, the maximum seismic loading represented by MHEA follows a well-defined trend.MHEA depends largely onthe initial fundamental period ofthe waste fill,Ts =4H/Vs , andthe mean period,Tm ,andMHA ofthe inputrock motion adjusted by the nonlinear response factor,NRF. Conversely, analytical results indicate that the MHA calculated at the top of a landfill can vary significantly for rela- tively modest variations in landfill configurations and input motions. Procedures that first require an estimate ofthe MHA at the top ofa landfill to estimate the seismic load- ingatthebaseofthelandfill arelimited bytherelatively largeuncertainty inestimating MHA at the top of a landfill. A rigid sliding block analysis can be significantly unconservative and should not be used. However, asa seismic performance index, a reasonable (and generally conserva-