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BRAY, RATHJE, AUGELLO AND MERRY D Seismic Design for Lined Solid-Waste Landfills 204 GEOSYNTHETICS INTERNATIONAL S 1998, VOL. 5, NOS. 1-2 1 INTRODUCTION Geosynthetics are a routine component of modern landfill design. The specification of geosynthetic components, such as geomembrane liners, in the waste containment system requires analysis of the overall response of the landfill. An important design consideration in seismic regions isthe evaluation ofthelandfill’sseismic performance. The current paper begins with a review of seismic design practice in light of observed landfill performance and,consequently, identifies issues relevant to thedesign ofcover andbaseliner systems, whichtypically incorporate several layersofgeosynthetics. The estimation of seismically induced deformations within these containment systems forms the basis of evaluating the likely performance of specific geosynthetic layers used in waste containment design. Hence, the current paper focuses on this issue. The seismic performance of waste fills is typically evaluated using analytical meth- odsdeveloped forseismic stability evaluations ofearth embankments, namely pseudo- static slope stability and seismically induced permanent deformation analyses. Al- though more sophisticated analytical procedures are available, such as coupled stick-slip finite element analysis (Gazetas and Uddin 1994), these procedures are not oftenutilized incurrent designduetotherelative uncertainties oftheinputstoananaly- sis(i.e. wasteandlinerproperties andearthquake groundmotions) comparedtothelim- itations ofcommonly usedanalytical tools. Hence, muchofthedevelopment inseismic designpractices formunicipal solid-waste landfills (MSWLFs)has beenin theapplica- tion of better understood analytical procedures, with attention to characterizing solid- waste and geosynthetic liner dynamic properties and evaluating the influence ofearth- quake ground motions on the likely seismic performance of MSWLFs. LargelyinresponsetoU.S.Federal regulations (UnitedStates Environmental Protec- tion Agency 1993, Subtitle D), seismic design procedures for MSWLFs in the United States have evolved rapidly over the past few years. In the current paper, recent devel- opments are critically reviewed to summarize the current understanding of seismic de- sign procedures for MSWLFs. Dynamic response and stability procedures are reex- amined in light of recent observations of the seismic performance of solid-waste landfills during the 1994 Northridge, California, USA and the 1995 Hyogoken Nanbu (Kobe), Japan earthquakes. Specific improvements to current U.S. design procedures are proposed. A newly developed simplified seismic analysis procedure requiring that the most critical factors be addressed is presented. This procedure has been validated against the observed performance of landfills shaken by recent earthquakes. The use of this procedure is illustrated in the seismic evaluation of a typical MSWLF unit. Althoughmuchprogresshasbeenmade since the 1988static failure oftheKettleman Hills Class I landfill in California, and a sound simplified seismic analysis procedure for MSWLFs can be proposed at this time, caution is warranted given the significant level ofuncertainty remaining in this field. With additional investigations and possibly new lessons to be learned from future earthquakes, design practices will continue to evolve, and the issues explored in the current paper will require reevaluation.