Seismic Analysis and Design of Retaining Walls, Buried Structures, Slopes, and Embankments (2008) / Chapter Skim
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Pages 96-104
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From page 96... ...
96 This chapter summarizes the results of embankment and slope stability studies that were carried out for the Project. The primary objectives of these studies were to: • Develop a methodology for evaluating the seismic response of embankments and slopes that can be easily used by designers; • Account for the results of ground motion and wave scattering studies presented in Chapters 5 and 6 in the proposed approach; and • Provide comments on the use of the proposed methodology in low seismicity areas, where a "no analysis" approach may be appropriate for the seismic analysis and design of embankments and slopes.
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From page 97... ...
For example, methods are described in detail in the FHWA report titled Geotechnical Earthquake Engineering (FHWA, 1998a) and a publication on Guidelines for Analyzing and Mitigating Landslide Hazards in California (SCEC, 2002)
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From page 98... ...
The seismic coefficient used in the analysis is based on the site-adjusted PGA adjusted for wave scattering effects using the α factor defined in Chapters 6 or 7. The vertical acceleration is normally set equal to zero based on studies that have shown vertical accelerations have a minor effect on the seismic stability evaluation for most cases.
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From page 99... ...
Similar discussions for slopes are presented in the FHWA publication Geotechnical Earthquake Engineering (FHWA, 1998a)
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From page 100... ...
100 Figure 8-5 shows a median prediction sliding displacement chart, normalized by kmax and D5–95, an earthquake duration parameter dependent on magnitude. For example, if ky/kmax = 0.2, kmax = 0.4, D5–95 = 10 seconds, then u equals about 15 inches, compared to about 6 inches (or 12 inches to achieve an 84 percent confidence level)
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From page 101... ...
Conduct static slope stability analyses using appropriate resistance factors to confirm that performance meets static loading requirements.
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From page 102... ...
for the various cases involved. With the yield acceleration, siteadjusted PGV, and the site-adjusted peak seismic coefficient (that is, PGA adjusted for site class and wave scattering)
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From page 103... ...
Parameter Slope Angle Static C/D Ratio kyield 7% in 75 Years 10% in 50 Years 2% in 50 Years Upper Bound Till (φ = 42 degrees) Case 1 1H to 1V 0.9 NA NA NA NA Case 2 1.5H to 1V 1.3 0.13 6-9 3-5 14-18 Case 3 2H to 1V 1.7 0.25 <1 <1 3-4 Upper Bound Till (φ = 38 degrees, c = 200 psf)
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From page 104... ...
The methodology uses conventional limit equilibrium slope stability analysis methods, in combination with the Newmark method for estimating displacements. Relative to existing methods, the approach: • Incorporates the results of wave scattering and ground motion studies summarized in Chapters 5 and 6, including an equation that relates the PGV to the spectral acceleration at one second.
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