Minimum Reinforcement in Auger Cast Pile

[Atooz]

I have seen an Auger cast pile with just two # 7 bars at the center in 16" dia pile, 50 feet deep. Which makes only close to .4% reinforcement. I think it should be minimum of 1 %. Any light this reinforcement. Has anyone seen such low reinforcement in ACIP piles.

Also my research has shown that minimum of 4 bars souls be provided with ties.

If anyone of you could shed more light on this, will highly appreciate. Thanks

 

[JedClampett]

I don't think Augercast has a minimum. I've seen 1% and I've seen no reinforcing, especially in the lower half. It seems though that older designs used less reinforcing.
I'm guessing it depends on potential for uplift and preference. Call your local installer.

 

[Ron]

No uplift, no reinforcement. Uplift....minimal reinforcement to hold the pile together in tension for a finite depth.

 

[BUGGAR]

That's probably better than hammering a code legal cage into partially set concrete.

 

[JedClampett]

BUGGAR, I thought the same thing until I watched them construct one of those. They follow the grout placement with the cage insertion very quickly. The only problem with the one I saw was that the cage tried to drop too fast. They needed to use the crane to control it.

 

[jdgengineer]

Chapter 18 of the IBC has requirements for deep foundation reinforcement. If you are in high seismic I believe you need 4 bars minimum with 0.5% ratio over a certain length of pier (as well as transverse steel requirements) We run full length typically.

 

[aeoliantexan]

I don't know what the codes require, and none of my comments apply to seismic design, but while I was in the Midwest, I saw a lot of augercast piles installed with only a 15-foot small cage in the top to tie it to the cap and handle incidental eccentricities. Early on, I think some only had dowels.

In Texas, one full-length bar down the center plus a short cage seems to be standard practice.

Installing full-length cages can be a problem for piles in sand. Some water bleeds out and makes the grout too stiff pretty quickly. Acting quickly may help, and if it won't go, the pile can be re-drilled and regrouted, and then it usually goes. But there's not much profit in that.

Although I don't see the full-length bar as necessary if no seismic and no uplift, I kind of like the practice because it is almost a test of the continuity of the pile. If soil is sucked into the pile, a bar with centralizers probably won't go down. Also, a #9 bar in compression adds some structural capacity that may help compensate for a flaw.