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102 Project Team.) The soil conditions are representative of The summary in Table 8-2 indicates that the displacements Site Class C. ranged from zero to a maximum of 73 inches, depending on assumptions made for soil properties and the design earth- The objective of the seismic stability study was to evaluate quake. Details for these analyses are included in Appendix J. the displacements that would be expected for the design earthquake. The owner also is interested in the risk to the 8.5 Other Considerations roadway facility, and therefore, stability also was evaluated for a 10 percent probability of exceedance in 50 years (475-year There are three other considerations relative to the seismic event) and for a 2 percent probability of exceedance (2,475-year design of slopes and embankments: (1) the use of the limit event). There is debate locally on the strength properties to equilibrium method for determining acceptability of slope assign till; therefore, each of the commonly used alternatives under seismic loading, (2) the acceleration level at which a is evaluated. "No Analysis" approach can be invoked, and (3) methods to consider when there is a liquefaction potential. These con- siderations are summarized below. 8.4.2 Results The ground motion criteria for the site were obtained from 8.5.1 Limit Equilibrium Design Methods the USGS website for the three return periods, as summarized in Table 8-1; local site effects were considered using the pro- Computer programs are routinely used for evaluating the cedures recommended in Chapter 5. static stability of slopes. As demonstrated in the example The computer program SLIDE was used to determine the problem, the incremental effort to determine ky is relatively static factor of safety and then the yield accelerations (ky) for minor. However, a particular state DOT may choose to de- the various cases involved. With the yield acceleration, site- velop a value of kmax to use either (1) in pseudo-static screen- adjusted PGV, and the site-adjusted peak seismic coefficient ing analyses (by calibrating against a displacement chart ap- (that is, PGA adjusted for site class and wave scattering), the propriate for seismic hazard levels in their state) in lieu of equations in Chapter 5 were used to estimate permanent dis- requiring a displacement analysis, or (2) if they feel a dis- placement. The estimated displacements from the analyses placement level different than the several inches identified in are summarized in Table 8-2. Section 8.3.1 is permissible. Table 8-1. Ground motions for example problem. Ground Motion Parameter Parameter Units Site Class 7% in 75 Years 10% in 50 Years 2% in 50 Years PGA B 0.41 0.31 0.58 Ss B 0.92 0.68 1.30 S1 B 0.30 0.22 0.44 Ss /2.5 0.37 0.27 0.52 Magnitude 6.8 6.8 6.8 Fpga C 1.00 1.10 1.00 D 1.10 1.20 1.00 Fv C 1.50 1.58 1.36 D 1.80 1.96 1.56 PGV In/sec C 25 19 33 In/sec D 30 24 38 = Fv S1 / Fpga PGA* C 1.10 1.02 1.03 D 1.20 1.16 1.18 Failure Slope Height ft 15 15 15 Factor per Equation 7-2 C 0.93 0.93 0.93 D 0.94 0.94 0.94 K av = PGA*Fpga * C 0.38 0.32 0.54 D 0.42 0.35 0.54