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OCR for page 77
77 Figure 7-14A. SLIDE calibration analyses for horizontal backfill (homogeneous soil conditions). of these analyses are used with the results of the analyses in detail in Appendix G. The initial set of SHAKE analyses re- Chapter 6 to develop recommendations for height-dependent peated many of the parameters originally evaluated by Seg- seismic design coefficients. restin and Bastick: 20-foot wall height. 7.5.1 Evaluation of Impedance Contrasts Three different shear wave velocities for soil supporting the and Soil Behavior wall (820 ft/sec; 1,200 ft/sec; and 3,300 ft/sec). Idriss mod- To examine the effects of impedance contrasts and nonlin- ulus and damping versus shearing strain curves for rock. ear soil behavior on height effects, one-dimensional SHAKE91 Compacted backfill within wall with = 30 degrees and (1992) analyses were undertaken and are documented in maximum shear modulus (Gmax) equal to 70 ( 0.5 m) . The

OCR for page 77
78 Figure 7-14B. SLIDE calibration analyses for horizontal backfill (nonhomogeneous soil conditions). Seed and Idriss modulus and damping curves were used to ternal stability evaluations in the AASHTO LRFD Bridge Design represent shearing strain effects. Specifications. Plots showing these comparisons are provided in Nine ground motions consistent with the discussions in Appendix G. These results show amplification at the top of the Chapter 5, including the two used by Segrestin and Bastick. wall, as well as maximum average acceleration along the wall height, similar to results from Segrestin and Bastick. However, These studies were successfully calibrated against studies un- the latter studies were limited to 20-foot high (6 meter) walls. dertaken by Segrestin and Bastick (1988) for MSE walls, which Additional parametric studies were subsequently con- forms the basis for MSE wall backfill seismic coefficients and ex- ducted to evaluate the effects of wall heights, impedance