Inadequate Cover Under Mat Foundation 2

[bookowski]

Just got an inspection report in for a 4'-6" mat that was poured 2 weeeks ago. The inspector notes that only 1" of cover was provided instead of the specified 3". Clearly this is not very useful 2 weeks out. I have notified the owner. Two questions:
- Owner is asking how it can be fixed. I hate to say that it can't, but short of pulling up 400 yards of concrete plus a story of walls I don't see any options?
- Beyond notifying the owner is there any other action to take?

 

[wannabeSE]

If the inspector can't certify that his initial inspection report is in error, one thought would be to have the contractor core the mat in a couple location (selected by SEOR with inspector input) and measure the cover. If they balk at coring that depth, let the contractor propose another method to expose the reinforcing.

 

[HouseBoy]

I don't know that this would be a compelling argument but... corrosion would not occur if there is not sufficient oxygen and I wonder if there would be a way to determine the oxygen levels under that mat as a way to substantiate the argument.
I don't know about low Ph but maybe that too could be determined.

Is 3" cover required for corrosion protection or is it required (for concrete placed directly against soil) as a way to be more certain that there is sufficient encasement to get bar development? (maybe both).

Seems like coring and evaluation the in place condition would be a good step before abandoning the sea in place.

What is the slab supporting? Big building or is this just for buoyancy resistance? (I've seen that before).

 

[jike]

What did the contractor use to support the bottom mat of steel? Did the rebar fabricator provide 3" chairs with sand plates or was some other support provided? I am not saying the inspector was mistaken but I wonder how could this could happen if 3" chairs were provided? Wouldn't this be called out on rebar shop drawings?

 

[BAretired]

Did anyone take a photograph of the steel prior to pouring concrete?

BA

 

[bookowski]

Back to this one. In the meantime: I advised the owner & owner's rep about the issue which they took very seriously. They notified the CM that they needed to propose a fix or show that this report was incorrect. The contractor chose to proceed in the meantime. Now we have walls and a couple of elevated slabs and the special inspector has just produced photos clearly showing deficient cover. These are photos without a tape or any reference but it is clear that we are looking at 1/2" to 1" areas, better in other areas. We're back at square one and the owner is demanding that the contractor prepare a proposed fix.

At the end of the day even if they submit signed and sealed repairs I'm on the hook. A tear out at this point is a huge deal so I'm not keen on rejecting a good idea to prove a point - but I'm having trouble imagining what their good idea could be. Is pressure grouting below the mat going to help/feasible/reasonable? Seems like the coring would need to be very frequent to ensure reasonable coverage. Combined with cathodic protection?

 

[KootK]

In the interest of preserving your sanity, could you:

1) Ask that a corrosion specialist be roped into the project at the contractor's expense.
2) Get the corrosion guy, contractor, and geotech at the same table.
3) Have the corrosion guy sign off on the fix with you nominally approving whatever they come up with?

This might ease your liability concerns and reduce the perception of your firm being the "bad guy". Basically, you delegate the bad guy job to someone more qualified.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[KootK]

Elevator pit is recessed into the footing, right? Any chance that you're confident that at least the rebar below/around the pit has adequate cover?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[bookowski]

Basically yes to elevator. That is my sleep at night card. The issue (at least as noted) is only in the area around the pit. If the rebar were to completely disappear in this area and the mat become ineffective it would mean that the surrounding soil becomes overstressed in bearing, i.e. I discount this portion of the mat. Since the bearing was controlled by lateral combos this means that in service we're still in ok shape.

I don't plan on giving them this out though since this is a major screw up and don't want to take it on my shoulders.

The corrosion/repair specialist is the route I am suggesting.

 

[bookowski]

Update in case anyone ever finds themselves in a similar boat. We're doing cathodic protection, compared to any type of tear out or partial tear out it is substantially cheaper, minimally disruptive to the ongoing work, and comes with a service life statement from the engineering company designing it.

 

[KootK]

Sounds like a decent outcome all things considered. Thanks for the update.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.