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Micropile installation "near" and "sufficient time" 2

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danyul

danyul

Geotechnical
Joined
Jun 16, 2006
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42
Location
US
Hello
I see in ibc 2012 1810.4.10 says 4. Subsequent micropiles shall not be drilled near elements that have been grouted until the grout has had sufficient time to harden.

I take that to mean that if you drill and grout a micropile, you can't drill another one nearby and within some time. Is there any more specific [pre][/pre]guidance for this?

Thank you
 
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I am not working in the US and dont have much experience with micropiles, however a quick google showed that after 24 Hours, grout fluid to ASTM C109 has a strength of 4000 psi (27.6 MPa) ( i would consider that sufficiently strong to allow drilling of next micropile. Therefore you could do a hit and miss construction.

To be honest my first thought was that it would be dependent on the spacing between piles (or would it be an issue at all if you were rotary?). Whats the reason for the delay in grouting until the first micropile grout would be cured....that drilling of the next micropile might somehow effect the dia of the 1st one. Surely this would be dependent on spacing...
 
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If there is a question such as this, I'd do an experiment to then control spacing, etc. Drill one and grout it. Then keep an eye on the level of grout while drilling the second nearly and grouting it. If there is no rise in the nearby mini-pile, no problem. If there is, widen the spacing and try again until no effect is noticed nearby.
 
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The term is "communication" and this comes up in low and high pressure grouting and CFA piling work.
Radius of influence depends on pressure and the ground stiffness. More pressure and/or soft soil = more cavity expansion, more fracturing, and more communication.
Many times, you cannot "keep an eye on it" because you don't have xray vision for deep piles. Nor does the contractor.
The code writers added something to the code(although ambiguous) because older versions of model specs from DFI and others were silent on this subject.
5 feet on center is a good place to start. Every other pile in a day is common.
 
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There is more to this than communication. Often there is a concern that drilling vibrations will reduce the grout bond or damage recently set but still weak grout.

 
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