Auger Cast Pile - Rebar Cover Tolerance
Auger Cast Pile - Rebar Cover Tolerance
(OP)
I have a project with 16" diameter auger cast piles and a cage with 7-#8 bars with #3 ties. We have specified a 3" clear for the cage, however some of the pile cages have come up with a 1 3/4" cover (project is under construction). To me this is out of specification per ACI 117 2.2.2 "-1/2 when member is over 12in" and/or ACI 318 7.5.2.1.
Are there any code requirements where we can reduce the required cover to less than 3"? Two of the piles out of tolerance are gravity only, the third is at a P5 lateral pile cap.
Is the solution to abandon the pile and construct a new one, I can't think of another repair solution.
Are there any code requirements where we can reduce the required cover to less than 3"? Two of the piles out of tolerance are gravity only, the third is at a P5 lateral pile cap.
Is the solution to abandon the pile and construct a new one, I can't think of another repair solution.






RE: Auger Cast Pile - Rebar Cover Tolerance
At the end of the day, if the piles need the reinforcement and it's not adequately covered, the service life of the pile and thereby the entire structure is pretty significantly reduced. I'll add the caveat that I don't have much experience with augercast piles, so take my opinions as you will.
RE: Auger Cast Pile - Rebar Cover Tolerance
As the drilling commenced, the Kelly bar and bit would have some degree of wobble in them, and the crane operator would have only limited ability to position the bit EXACTLY at the pier centerline.
So if you used an 18" diameter bit, you'd usually end up with a 20" or larger earth shaft. So a cage fabricated to 14" diameter (2" clear on an 18" shaft) would actually have 3 to 4 inches of clearance.
With a flight auger you may not have that degree of wobble or over-cut on the shaft but you could investigate that with some other subsequent shafts.
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RE: Auger Cast Pile - Rebar Cover Tolerance
As a former bridge contractor, suggest not being to "harsh" on this spec deviation. The key to what is "harsh" may depend on who designed the rebar cage, your firm or the contractor?
1 3/4" cover may be pretty good for this type real world construction, unless corrosion issues which phamODU pointed out are a known concern.
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RE: Auger Cast Pile - Rebar Cover Tolerance
The auger cast piles I've seen use these centralizers. They seem fool proof. Allow the one bad one and make them use them in the future.
RE: Auger Cast Pile - Rebar Cover Tolerance
It sounds like the OP is just saying the cages are too big. I don't know how you actually determine how far the reinforcement ends up from the edges of the excavation.
RE: Auger Cast Pile - Rebar Cover Tolerance
The pile contractors engineer has requested the loads for the piles in question and will redesign the piles ignoring the rebar that is outside the 2" cover. However, we have a concern about the possibility of these bars corroding and spalling the face of the pile below grade. Has anyone seen this suggested repair before where the bar is ignored for design?
RE: Auger Cast Pile - Rebar Cover Tolerance
As long as the pile is laterally restrained (by the soil, even), there should be no issues.
Dik
RE: Auger Cast Pile - Rebar Cover Tolerance
Are cages too big, or inadequate/no centralizers?
RE: Auger Cast Pile - Rebar Cover Tolerance
RE: Auger Cast Pile - Rebar Cover Tolerance
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RE: Auger Cast Pile - Rebar Cover Tolerance
Where are you measuring the achieved cover? Top of pile, or can you get that somehow along your pile length?
Certainly I'd be OK with the gravity piles being out of alignment (assuming your soil isn't total swampy junk). Like dik mentioned, the rebar is only in those to help us feel good, maybe some ductility/durability, and connection to your structure.
If you were talking about a flagpole (large moments), I'd feel differently.
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RE: Auger Cast Pile - Rebar Cover Tolerance
Or the auger flights are worn
Or the hole is squeezing or sloughing
Or the superintendent has no idea what he is doing
Or the crew is using the wrong type of centralizers
ACIP is very dynamic, requires a much higher level of training and inspection
RE: Auger Cast Pile - Rebar Cover Tolerance
It's not like the piles are scantily reinforced. Seven #8s is something like 2.8%. That's a lot of reinforcement in a gravity pile.