Scanning Pile Rebar From the Top 1

[KootK]

I've got some piles that were constructed without being inspected. Some testing was done to confirm the pile depth but I'm being told that it is not possible to scan the rebar from the top of the pile in order to ascertain at least the rebar circle (right side sketch below).

Is is problematic to scan pile rebar from the top? The verticals will be more important than the ties for this.

 

[EZBuilding]

Don't have any feedback on the scanning, but would you be able to chip out the top portion of the pile to verify the rebar and repour?

 

[Howlyn2]

KootK. Can you dig along the side and scan from the side? Typical Foundation NDTs - Non Destructive Testing - "rolls" the scanner around / along the perimeter. Spacing is marked with a grease pen, measured in the field, and confirmed on the computer back in the office once the data is uploaded. Scanning from the top is not possible b/c the scan would hit the "tips" of the longitudinal bars. You need a full surface across the width of the scanner ~8" to identify the change in density btwn the two materials. Hope that helps.

 

[Enable]

I've never had this come up. But here are a few spitballs (take em or throw em right on back):

A) The GPR device has some distance to the side, for wheels and such, so you cannot scan all the way to an edge. Maybe they're concerned about proximity of the vertical bars to the edge such that they won't be caught in the scan.



B) GPR reports discontinuities via radio wave bounces and isn't actually "seeing" the rebar. It's rather difficult to distinguish what is what and takes a bit of back and forth (over some length of bar) for the operator to do this reliably. Perhaps the butt ends of rebar will produce only such localized discontinuities that it would be difficult to detect (or impossible to) with the desired degree of reliability.

According to one tech guide you can only pickup items perpendicular to the scan direction, so this seems likely.



If chipping is not an option (as mentioned above) X-Ray is also another possibility. FWIW Xradar works in Calgary, and I am reasonably sure that they will have the equipment to get whatever you need done (https://www.xradar.ca/).

 

[GC_Hopi]

A lot of what you see will depend on the skill of the GPR operator. I have only see and been told by GPR companies that the maximum reliable depth is 10 inches. Scanning down to see the ends of vertical rebar will be quite challenging. Also GPR will not get you information on rebar diameter.

Chipping on a select few piles (random piles and also critical load piles) would be my thought. Does the contractor have any photos? What is driving you to do investigation... field issues, building official, or suspicions.

 

[KootK]

but would you be able to chip out the top portion of the pile to verify the rebar and repour?

It's possible but, as you might imagine, would not be popular. This is a pretty minor structure and the chip and report would feel like "a bit much".

 

[KootK]

Can you dig along the side and scan from the side?

Also possible. The one hang up with this is that, precisely because this is a small scale thing (6' embed), I'm a bit leery of disturbing the top bit of the embedment. Although, technically, I guess that I'm supposed to ignore it anyhow for frost effects. This may well be my path.

Scanning from the top is not possible b/c the scan would hit the "tips" of the longitudinal bars. You need a full surface across the width of the scanner ~8" to identify the change in density btwn the two materials.

Thanks you for that. It is a great help for me to be able understand the "why" of the problem.

 

[KootK]

FWIW Xradar works in Calgary, and I am reasonably sure that they will have the equipment to get whatever you need done (https://www.xradar.ca/).

Thanks for that. This is actually in TO.

 

[KootK]

Does the contractor have any photos? What is driving you to do investigation... field issues, building official, or suspicions.

No photos.

Driven by building official I suppose. I have to sign off on some paperwork confirming that I've observed the salient features of the construction. Like a much weaker form of the special inspection business in the US. What I've got is this:

1) Testing confirming the pile depth (only two piles).

2) Paperwork confirming that the contractor received the rebar cages from my client.

3) The general understanding that the structure is minor. If I could bank on the piles not cracking, I'm sure that it would work unreinforced.

As is often the case, I'm trying to straddle the reasonable / responsible boundary.

 

[EZBuilding]

At 6' depth this feels closer to an embedded post type of concrete foundation than what I would categorize as an actual deep foundation "pile".

Seeing as how the loads are minor, I would take a stab at considering the capacity of the embedded post as a Plain Concrete element as a lower-bound approach to justifying the whole situation.

 

[KootK]

At 6' depth this feels closer to an embedded post type of concrete foundation than what I would categorize as an actual deep foundation "pile".

Just so.

 

[KootK]

I would take a stab at considering the capacity of the embedded post as a Plain Concrete element as a lower-bound approach to justifying the whole situation.

So, even though this will behave much like an embedded post, it is not an embedded post. The stuff on top is anchor bolt mounted.

If it were truly an embedded post, I would not sweat pile cracking as the post itself can sort of be the flexurally continuous thing. Given that, is there any worry about the pile cracking due to frost jacking etc in such a manner that it would compromise the unreinforced flexural capacity? I feel that is.... at least remote.

 

[Just Some Nerd]

2) Paperwork confirming that the contractor received the rebar cages from my client.

Does it confirm the details of the piles match what you need? If the total number delivered and the reinforcement details are correct from the supplier, I'd be more willing to limit how many piles need to get scanned.

 

[KootK]

Does it confirm the details of the piles match what you need?

It does, yes.

If the total number delivered and the reinforcement details are correct from the supplier, I'd be more willing to limit how many piles need to get scanned.

There are only two piles. So I would be scanning half of them or all of them!