MICRO PILE DRILLED OR AUGUERED?

[PT999]

8" Micro-pile, Steel Cased for 1/2 depth, uncased for the bottom 1/2, grout filled with all-thread rebar.

Is it augered or drilled?
NYC Building Code (2008) (Section 1810.3) calls for different allowable concrete stresses when drilled (33% of fc, vs 25% of fc for auguered)

Why and which applies?

 

[PEinc]

I'm not sure and don't have my NYC code with me but I would assume that the higher concrete is allowed because the drilled micropile has a known diameter due to use of a drill casing. If the micropile is installed just by augering a hole (no casing used), there may be concern that the concrete shaft is not necessarily the desired diameter due to some sloughing of the soil. BUT, that's just my guess.

http://www.PeirceEngineering.com

 

[Teguci]

IBC uses a 25% of concrete compressive strength for uncased concrete piles (CIP) and 33% for cased. However, IBC specifically calls out 33% for micropile grout when encased and 0% for uncased grout (full load in rebar). It seems to me that NYC is neglecting their building code and hasn't specifically addressed the micropile design. Be careful though, there is an 8" minimum diameter limitation built into the standard concrete pile design which most micropiles do not meet.

As always, talk to the bureaucrats and determine haw they want you to proceed.