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Pile skin friction during an earthquake?

Pile skin friction during an earthquake?

Pile skin friction during an earthquake?

(OP)
I have a question about a project I never felt comfortable with.  
A few years ago, I inspected pile driving for a building built entirely on timber piles, a number of which simply didn't meet the criteria upon initial driving.  It was only after we ran into this shortcoming that the engineer agreed to re-driving the piles- it just seemed flimsy.  If the engineer was competent enough to recommend pile criteria in the first place, why didn't he include re-drive criteria along with it?  Not only that, but if competency depends 75% on skin friction, what happens when the case of an earthquake, when those particles are put in motion?  I was in good-old-boy territory over there, so that may have had something to do with my questioning.  Is this all due process for piles engineered mostly based on skin friction?  

RE: Pile skin friction during an earthquake?

Where was the site?  What were the soil conditions?  Groundwater conditions?  Pile size (length)?

The only condition that I really worry about friction in earthquakes is when the soils are 'cohesionless' or 'semi-cohesive' and may contract under shearing.  Liquefiable silts and fine sands are the principal problem soils, at least in my view.  I guess that I would add quick clays to that list, although I wouldn't design them for friction in an earthquake prone area.  Heck, they couldn't be counted on for much friction anyway.

If the sands are dense and dry, I don't worry at all.  If the soils are moderately strong clays, ditto.

What is the failure mechanism that concerns you?



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