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Double-walled micropile?

Double-walled micropile?

Double-walled micropile?

From this: thread815-412357: SF tower settlement and this SF Chronicle article: Link

The following photo references a 13-5/8" dia micropile:

So the outer wall is a casing, and the inner bar is threaded (and coupled) structural reinforcement, what is the inner wall?

Is the inner wall primarily for providing additional structural axial capacity?

Seems like significant additional effort for installation, and also to grout the outer annulus.

Are such micropiles common?

RE: Double-walled micropile?

The Millennium Tower was the first that I've encountered double walled micropile. They have to do something to justify the $1M price tag per pile...


RE: Double-walled micropile?

Thanks Dik. First time for me too, hence the inquiry.

Maybe they are also gold plate and diamond encrusted too, given the price tag!

RE: Double-walled micropile?

That threaded bar looks to be 50mm or 2' approx, would that be upper limit of what you would put in a micropile ? Never really encounter them here in the UK.

RE: Double-walled micropile?


Quote (EireChCh)

That threaded bar looks to be 50mm or 2' approx, would that be upper limit of what you would put in a micropile ? Never really encounter them here in the UK.

#28 (3-1/2" or 90mm) Grade 75 ksi (520 MPa) is the largest dia available in the US, to my knowledge. Sometimes (not very often) 2 smaller dia bundled bars are used, but not too common due to the slower production of installing bundled and coupled bars.

150 ksi (1035 MPa) grade is also available up to 3" (75mm) diameter:

From the thread I referenced above a link was provided by epoxybot that details the micropile section:

Damn, that inner casing has a 1-1/8" thick wall.

Note the 1/4" weld bead around the entire circumference of the outer casing, at 6" c/c!!!!!

RE: Double-walled micropile?

so much for being "micro"

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