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BRAY, RATHJE, AUGELLO AND MERRY D Seismic Design for Lined Solid-Waste Landfills 223GEOSYNTHETICS INTERNATIONAL S 1998, VOL. 5, NOS. 1-2 The yield acceleration coefficient recommended by Buranek and Prasad (1991) was used for the Loma Prieta earthquake case records, and ky was calculated with the 2-D limit equilibrium slope stability analysis program UTEXAS3 (Wright 1990) for the Northridge earthquake cases using the strength values recommended by Augello et al. (1995). The median and 16% probability of exceedance kmax values were estimated us- ing Figure 6 based on the median estimates of Ts ,MHARock ,andTm shown. The calcu- lated displacements,U, were then estimated using the median and 16% probability of exceedance lines shown in Figure 11. The calculated earthquake-induced displacements are consistent with the magnitude ofpermanent displacements observed atthese landfills. Generally, nocracking wasob- served when the calculated displacement waszero, and some distress was observed for cases when the calculated displacement was nonzero. Asthe calculated earthquake-in- duced displacement should be viewed as merely an index of earthquake performance, the proposed procedure isjudged to provide an index ofexpected seismic performance that correlates reasonably well with the actual seismic performance of these landfills. 3 SIMPLIFIED SEISMIC ANALYSIS PROCEDURE 3.1 General A two stage, simplified seismic analysis procedure is outlined in this section. This procedure isbasedontheanalytical results discussed inSection2whichhavebeenvali- dated against the observed performance of lined and unlined solid-waste landfill units shaken by the 1989 Loma Prieta and 1994 Northridge earthquakes. Although “simpli- fied”, the procedure iscomprehensive in that it requires that the most important factors be addressed during a seismic performance evaluation, namely: (a) characterization of the design bedrock motions in terms of intensity, frequency content, and duration; (b) estimation of the seismic loading at the base and cover of the landfill; (c) evaluation of performance in terms of seismically induced permanent deformations; and (d) ap- plication ofappropriate engineering judgment.Astraightforward, conservative screen- ing analysis is incorporated as the first stage of the procedure, and situations that war- rant more sophisticated analysis are identified. The screening analysis employs a reasonable level of conservatism by including the following: amplification factors in the range of 1.2 to 1.5 (see Figures 6 and 8 at Ts /Tm < 0.75); a value of NRF =1which is appropriate for the larger values in Figures 6 and 8; and a seismic coefficient cali- brated using Figures 11and 12(i.e.k =0.55kmax )forcalculated seismically induced dis- placements generally lessthan150and300mmforbase andcover sliding, respectively (i.e. 10% probability of exceedance). 3.2 Screening Analysis Note that very deep, soft clay sites and sites susceptible to liquefaction (UBC Site Category SF) are not applicable to this screening analysis. Also, unstable geologic site conditions, suchasnative slope instability and surface faulting, shouldbe assessed sep- arately. The following is an outline of the screening analysis: 3.2 Screening Analysis