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OCR for page 79
79 Figure 7-15A. SLIDE calibration analyses for sloping backfill (homogeneous soil conditions). contrasts, and accelerations levels, using the same SHAKE 7.5.2 Results of Impedance Contrast models: and Nonlinearity Evaluations Response evaluated at wall heights of 20, 50, and 100 feet. Results of the studies summarized above and described The low-strain shear modulus changed to Gmax = 59 ( m) 0.5 in Appendix G generally follow trends similar to the wave to correspond to a relative density of 75 percent, which was scattering studies described in Chapter 6. However, based judged to be more realistic. on a study of the results and to simplify the results for the Nine ground motions used as noted above. development of recommended specifications and commen-

OCR for page 79
80 Figure 7-15B. SLIDE calibration analyses for sloping backfill (nonhomogeneous soil conditions). taries for the AASHTO LRFD Bridge Design Specifications, Curves in Figure 7-16 from Chapter 6 are for slightly differ- the use of a simple linear function to describe reductions in ent equivalent values than shown for the simplified approach. average height-dependent seismic coefficients, as shown in These values are 1.7, 1.1, and 0.4 for UB, mid, and LB spectral Figure 7-16, is recommended. Comparisons with the curves response, respectively. The differences in the values explain resulting from the height-dependent scattering studies also the difference between the locations of the lines for the curves are noted in Figure 7-16. from Chapter 6 versus the simplified straight-line functions.