Site response for dummies for liquefaction analysis 1

[DougHole]

i was just wondering what the difference is between the following analysis methods used to calculate the CSR for a liquefaction analysis in a site response analysis:

1. linear total stress (SHAKE?)
2. non-linear total stress
3. non-linear effective stress

what does the "linear" thing mean? does that mean that when the soil is shaken it behaves elastically (i.e. just deforms a little bit) and non-linear means that when it is shaken, it deforms a lot i.e. elastic ("linear") to begin with and then plastic after that (non-linear).

Also, what does the total stress and effective stress thing mean in this context?

 

[Mccoy]

Doughole

Linear elastic methods: as you say, it implies a liear elastic response, when the stiffness degradation of the soil layers crossed by seismic waves is not significant. This happens typically in rigid soils and with low-intensity earthquakes. LE methods are also used to compare the theoretical response model to empirical H/V measurements

Equivalent linear: the degradation of soil layers is significant and this goes together with the increase in damping ratio. It is a must in strong earthquakes and weak soils. It implies a stepwise iterative linear elastic response which mimics the nonlinear response in reality.

Non linear: it is a must in liquifiable soils,in very weak soils where plastic effects are expected, in soils where fluid pressure effects are not negligible; also can be more accurate in thick deposits of not very rigid layers, avoiding effects such as overdamping of high frequencies. Cons are model uncertainties and more complex analysis and interpretation.

Total stress: no pore fluids effects are considered
Effective stress: pore fluid effects versus time are considered

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