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Report - Oregon State Library: State Employee Information Center ...

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10.0<br />

0.0<br />

-10.0<br />

Foundation Soils (SM/ML)<br />

-20.0<br />

-30.0<br />

Sand<br />

Elevation (m)<br />

-40.0<br />

-50.0<br />

157<br />

-60.0<br />

-70.0<br />

Troutdale Gravels<br />

-80.0<br />

-90.0<br />

Sandy River Mudstone<br />

-100.0<br />

0 200 400 600 800 1000 1200 1400 1600<br />

Shear Wave Velocity, V s (m/sec)<br />

Figure 8.10: Shear Wave Velocity Profile at Location 4E<br />

8.5.1 Dynamic Response Analysis Method, SHAKE91<br />

The SHAKE91 program (Idriss and Sun 1992) was used to compute the response of the<br />

subsurface to vertically propagating shear waves. The program assumes the subsurface consists<br />

of visco-elastic, isotropic, and homogeneous material (soil) of infinite horizontal extent. Each<br />

layer is also assumed to be completely described by shear modulus (G), damping ratio ()total<br />

unit weight (), and layer thickness (h). The continuous solution to the wave equation is the basis<br />

for SHAKE91. The wave equation is adapted for use with transient motion through the use of the<br />

Fast Fourier Transform algorithm. Because the analysis uses the Fast Fourier Transform, and<br />

therefore, the frequency domain, it is a linear analysis. However, G and are nonlinear, straindependent<br />

soil properties. The nonlinearity of these properties is accounted for by using an<br />

iterative, equivalent nonlinear procedure to find strain compatible modulus and damping ratios

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