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EVALUATION OF MSW PROPERTIES FOR SEISMIC ANALYSIS Edward Kavazanjian, Jr.1 , Member, ASCE, Neven MatasoviC2 , Associate Member, ASCE, Rudolph Bonaparte', Member, ASCE, and Gary R. Sclunertmann4 , Associate Member, ASCE ABsrRAcr In situ me~sureme?ts and observations of field performance provide a valuab_Ie source of mformatlon on the properties of municipal solid waste (MSW) f analysis of landfills. "Static" properties of MSW such as unit weight and she or ~tren~ are evaluated from observations made during and after waste placemen~ mcludm~ records of tonnage of waste received and cover soil used during disposal' observations of stable MSW slopes and in situ load tests. "Dynamic" properties of MSW such as modulus ~d damping are evaluated from observations of the performance of landfills subject to strong ground motions and by geophysical testing. INTRODUCTION . S~ismic design of MSW landfills is complicated by difficulty in obtainin inform~t1on on th~ p~opertie.s .of MSW. Difficulties in evaluating appropriate Ms.J ~roperti~s .. for sets~tc stability and deformation analyses are not limited to the dyruu~:uc propertte~ of small strain shear modulus and strain-dependent modulus reduction. and.dampmg factors. Approp~iate values for the "static" properties of MSW urut weight and shear strength reqUired for seismic stability and defonnatio analyses are also:difficult to establish. The selected value of these static propertie~ 1Associate, GeoSyntec Consultants, 16541 Gothard Street Suite 211 Huntingto Beach, CA 92647 ' ' n 2~enior Staff Engineer, GeoSyntec Consultants, 16541 Gothard Street Suite 211 Huntmgton Beach, CA 92647 ' ' 3~incipal, GeoSyntec Consultants, 1100 Lake Hearn Drive, Suite 200 Atlanta Georgra, 30342. ' ' 4Senior Project Engineer, GeoSyntec Consultants, 1100 Lake Hearn Drive Suit 200, Atlanta, GA 30342 • e 1126 I' I i' ! I MSW PROPERTIES 1127 can have a significant influence of the results of dynamic analyses. Considering the difficulty associated with the evaluation of MSW properties, design engineers often rely on sensitivity studies and conservative assumptions in perfonning and interpreting the results of seismic analyses for MSW landfills. The conventional approach to establishing geotechnical properties of field sampling and laboratory testing is of limited value in evaluating the properties of MSW. Limitations of this approach include constraints on sampling of MSW related to health and safety issues and the small size of test specimens relative to the inhomogeneity of waste and the sizes of the waste constituents. Considering these difficulties, in-situ measurements and observations of field perfonnance provide perhaps the best means of evaluating the properties of MSW for seismic analyses. SEISMIC Ai"'ALYSIS OF SOLID WASTE LANDFILLS Seismic stability and defonnation analyses of MSW landfills rely primarily upon methods developed for seismic analysis of earth structures (Seed and Bonaparte, 1992; Repetto et al., 1993). Seismic analyses for MSW landfills typically employ pseudo-static limit equilibrium stability analyses to evaluate the yield acceleration of potential slip surfaces and seismic response analyses to assess the acceleration response of the waste mass. If the peak average acceleration of the failure mass from the seismic response analysis exceeds the yield acceleration from the limit equilibrium analysis, a "Newmark" seismic deformation analysis is perfonned to evaluate the potential for pennanent seismic defonnations. The Newmark permanent seismic defonnation analysis is based upon the yield acceleration from the stability analysis and the acceleration response of the waste mass from the seismic response analysis. Pseudo-static limit equilibrium stability analyses are usually perfonned using standard computer programs for geotechnical slope stability analysis. Seismic response analyses of landfills typically employ standard computer programs for equivalent-linear one-dimensional site response analysis. Permanent seismic deformation analyses typically employ either a computer program developed for the specific purpose of implementation of Newmark's method for calculating seismic displacement or charts developed from Newmark analyses perfonned by previous investigators. MATERIAL PROPERTIES FOR SEISMIC ANALYSIS The waste properties required for the seismic analysis of landfills are the same as the soil properties required for seismic analyses of earth structures. For pseudo-static limit equilibrium stability analyses and one-dimensional equivalent- linear site response analyses, the required properties include unit weight (or mass density), initial shear wave velocity, shear modulus reduction curve, and equivalent viscous damping curve. The initial shear wave velocity together with mass density defines the initial, small strain, shear modulus. For the "static" waste properties of unit weight and initial shear wave velocity, it is important to provide the distribution versus depth, and not just a single representative, or average, value for these parameters. Kavazanjian and MatasoviC