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Earthquake Induced Settlement

Earthquake Induced Settlement

(OP)
Hi all,

I am working on a reclamation/cover design for a (uranium) tailings impoundment. Following our initial design, we have recieved comments from the regulatory agency (and their consultant). One of the comments requests that we perform a seismic settlment analysis on the (mostly) dewatered tailings. Does anyone know of a fairly recent reference that addresses how to perform such an analysis? I am aware of the 1987 Tokimatsu and Seed method, but fear that it is too dated and will result in another round of comments requesting a more current method.

Thanks in advance for any help.

RE: Earthquake Induced Settlement

Wait a minute. You say dewatered tailings, but Tokimatsu and Seed is for reconsolidation of liquefied material (saturated) after the earthquake is over. The dewatered portion of your tailings could be better or worse depending on material properties (density, water content/degree of saturation, grain sizes, Atterbergs etc.), M (as a proxy for number of cycles), cyclic strain, overburden stress, etc. How dewatered is "dewatered"? At one extreme, it would be like clean dry sand in the lab maximum density test (with the vibrator switched off after half a second). If it's fine-grained and has capillarity, it could be better. It's got high void ratio, right? Compare the present void ratio with how low could it possibly go from shaking.

If there are significant thicknesses of material that is still saturated, expect a few percent volumetric strain, as indicated by Tokimatsu and Seed or Ishihara and Yoshimine. (Refer to the EERI monograph that FixedEarth mentions.) Tokimatsu and Seed does reasonably well, and I'm not sure any other method is going to give an answer that is a whole lot more believable.

On the other hand, unless the whole impoundment is pretty flat, settlement due to shear strains may come out a whole lot worse than what's caused by volumetric strain. Be sure you're looking at the whole problem, or at the right problem.

Regards,
DRG

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