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1134 GEOENVIRONMENT 2000 over a depth interval of 6 to 23 m. Woodward Clyde Consultants 01/CC, 1987) reported an average shear wave velocity of between 206 and 244 m/s from seismic refraction surveys for. the Oil landfill. For the same landftll, Hushmand Associates (1994) reports that ambient vibration measurements and measurements of ground motions from small magnitude earthquakes yield a predominant period of between 0.8 and 1.2 seconds for the landfill. Using the maximum reported waste thickness of about 76 m, these periods correspond to average shear wave velocities of between 244 and 366 rnls as back calculated by the authors. The field measurements of MSW shear wave velocity cited above, plotted on Figure 3, were interpreted by the authors to develop a typical profile for use in seismic analysis. In developing this profile, the relatively high velocities from the cross~hole results from Brookhaven were discounted due to uncertainty about the depths of the measurements. Cross hole data is also suspect because of the potential for "short circuiting" of the travel path between boreholes by the daily cover layers. The down-hole results and the ambient vibration and earthquake motion-derived values were considered as average values to which the typical profile should confonn. Based upon these considerations, the shear wave velocity profile shown on Figure 3 was developed for use in seismic analysis of MSW landfills in the absence of site-specific data. Tbis Study ··-···· Kavazanjian et aL {1994) (B sites)\ --after Carey et al. (1993) \ .... Sharma et aL (1990) .fAA~W!i Woodward-Clyde Consultants (1987) ~'~'!'''''~ ~f:~ :~:£FT~c~~i~;;a[19a~\9 f~:osshole) -·-after Earth Technology (1988) (downhole) SHEAR WAVE VELOCITY (m/s) FIG. 3 Shear Wave Velocity of MSW EQUIVALENT-LINEAR PARAMETERS FOR MSW Due to a lack of documented case histories, current practice for seismic response analysis of MSW landfills relies primarily on engineering judgement in choosing equivalent-linear response parameters for MSW. Modulus reduction and MSW PROPERTIES 1135 damping curves are typically assumed to correspond to previously established curves for clay or peat (Eartb Technology, 1988; Singh and Murphy, 1990; Shanna and Goyal, 1991; Seed and Bonaparte, 1992; Repetto eta!., 1993). The same effectiVe strain factor used in the analysis of earth structures IS usually assumed for analysis of landfills. Until recently, neither cyclic testing data nor field observations of the response of landfills to dynamic loading have been available for evaluation of the equivalent-linear properties of MSW. Strong motion records recorded at the OII landfill in recent earthquakes have, for the first time, provided data for evaluation of the equivalent-linear parameters of MSW. Two strong motion recording stations, one at the crest of the landfill and one at an outcrop adjacent to the landfill, have been operated at the landfill site since 1989. These stations have captured ground motion records from five earthquakes of magnitude greater than 5.0 with peak horizontal ground accelerations (PHGA) from 0.03 g to 0.25 g at the outcrop and from 0.05 g to 0.26 g at the crest (Hushmand Associates, 1994). Among the most significant of these records are those from the 17 January 1994 M 6.7 Northridge earthquake, where recorded PHGA were 0.25 g at the outcrop and 0.26 g at the landfill crest, and the 28 June 1992 M 7.4 Landers earthquake where the PHGA at the outcrop of 0.03 g was amplified by a factor of three to yield a PHGA of 0.09 g a~ the land?ll crest .. Back analysis of the OII strong motion records provtdes a rat10nal basis for the evaluation of the equivalent-linear response parameters of solid waste. While Oil is not a "typical" MSW landfill in that it received both industrial and liquid wastes while in operation, it is primarily composed of MSW. Therefore, in ~e absence of any other data, modulus reduction and damping curves and an effective strain factor back calculated from the observed response at on provide the best available infonnation for evaluation of the equivalent-liner properties of MSW · A plan view and cross section showing the location of the two strong motion record~ng stations at the Oil landfill is presented in Figure 4. Figure 5 shows the acceleration time histories in the longitudinal direction (parallel to Section B-B' in Figure 4) from the Northridge and Landers events at the outcrop and at the crest of the landfill. Best-fit equivalent-linear parameters for MSW were visually identified through trial and error using the computer program SHAK£91 (Idriss and S~n, 1992) and the strong motion records shown in Figure 5. The analyses used damp10g and modulus reduction curves for peat from Seed and Idriss (1970a), clay from Seed and Idriss (1970b), plasticity index of 15 from Vucetic and Dobry (1991), and MSW from Kavazanjian and MatasoviC (1994). The clay and peat curves were used based upon the recommendations of previous investigators (Earth Technology, 1988; Singh and Murphy, 1990; Shanna and Goyal, 1991; Repetto et al., 1993). Kavazanjian and Matasovi~ developed ~eir MSW curves from results of non-linear time-domain analyses usmg the Mod1fied Kondner-Zelasko (MKZ) constitutive model (MatasoviC and Vucetic, 1993) back-fit to the OII strong motion records. The Kavazanjian and MatasoviC modulus reduction and damping curves for MSW, shown in Figure 6, were then developed using the best-fit MKZ parameters to model the hysteretic behavior of MSW in unifonn cyclic loading.