We're doing a kitchen remodel that includes trenching the slab in order to run gas to the island that previously had an electric cooktop. They took the most direct path from the nearest gas source (in the laundry room) and exposed seven post-tension cables. The sheathing is nicked on a few of them. One of them is completely severed with a gap of 2-3 inches.

Any thoughts on what this might cost to repair and/or how this could affect foundation stability?

You're going to need to talk to an engineer to figure out the answer to either of these two questions. Could be unaffected, might need repairs. Not enough information to go by at this point.

I think you're stuck with it and will have to play the wait and see game.

Wow. Notify your contractor that you're hiring an engineer and will be withholding their funding to pay for it (assuming your contract allows for this) and then hire an engineer.

And tell them to put their carrier on notice.....

The cut cable can be pulled and replaced and the sleeves on the others will need to be repaired. It is not any easy or cheap process but it is reparable. You absolutely need an engineer to design the repair. They may say replace the cable or they may add some steel reinforcement in that area or both.

If only one cable they can probably design some steel to reinforce

Thanks for the input so far...here's 2000 words...hopefully I figured out how to post pictures correctly...

Where are you located?

Repair depends if bonded or unbonded cable.

Good Lord....were they cutting through your floor with a set of 5 stacked timber cut blades? How do you end of removing that much cable?

We're in Plano. They indicate it was repaired today but I don't have details yet. Generally, we trust this contractor as they did our master bathroom a while back with minimal issues.

Regarding bonded vs unbonded, my understanding is that it is unbonded since I see a sheath on it with some sort of grease but I only know what I have researched online in the last 24 hours (i.e. didn't know what a post-tension slab or cable was before finding the broken cable last night). I will say that I have never seen any warnings stamped in the concrete to not cut or core the slab like I see online for post tension slabs.

Regarding the distance between the ends of the cable, I'm assuming that is how far the cable retracted since it is no longer under tension. I believe they were using some kind of saw to make the cuts and then jackhammering out the chunks.

I find it very surprising that they were able to properly repair it so quickly. Ask for the sealed detail they used from a licensed engineer.

If you want to get an independent engineer involved (which I highly recommend), Don Illingworth is in Arlington. He helped write some of the codes for PT slabs so he knows his stuff.

Disclaimer: I don't and have never worked for Don but I hear he is a good dude.

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Don't let them re-fill the trench with concrete until you have a signed/sealed repair plan from a PE. If they repaired and you weren't aware, that sounds like they're trying to hurry and bury their mistake.

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This. And from the perspective of a lawyer, document everything in writing. Even if you have a telephone call or in-person meeting. Followup with an email summary recording what has/is/was said.

Did they know it was PT when they started the project?

Here's the repair:


Contractor indicates this is fairly common occurrence and the repair is sufficient.
My google-fu tells me it's called a splice chuck. It is not clear to me how or if full tension is able to be put back on it.

We had foundation work done last year that was approved by an independent engineer. He's not in business to work for free but I'm hoping I can call him tomorrow morning and get an answer on whether the splice chucks are a viable repair.

Call me skeptical, but I would not accept it. If it's so common then why wasn't more care taken when trenching that out?

Don't buy it. Doesn't pass my smell test.

There is no easy/good answer to this issue.

IF the cable was in a sleeve (post tensioned) the repair is relatively useless when soil movement occurs and a crack "somewhere" is probably going to happen - UNLESS there is a complete web/network of these cables throughout the foundation. At least you appear to have many others running in both directions. And, if engineered properly, each probably has a "safety factor" of at least 2 - if not 3. The whole point to post tension is to keep the slab together and not allow a crack to widen if indeed one occurs. Do you have any other known "cracks" (however tiny) anywhere else in your slab that might indicate a weakness in the foundation design? Agreed, these post/pre tensioned slabs are one of the best ways to resolve soils with heavy clay, or in a flood zone, high water table, etc...

Indeed, with as big a trench in the slab as shown, the slab already has a massive "expansion joint" just waiting to crack - I'd be as worried about that big trench as the cut cable....

IF the cable was bonded to the concrete like a normal rebar (pre tensioned and then concrete placed), the repair is about as good as can be had and should easily suffice. Still doesn't solve the trench/expansion joint issue however.

The idea that the entire slab should be re-engineered and redone is way beyond cost efficient and not very practical.

What does your insurance agent say?? ...or rather, what does the contractor's insurance agent say to YOUR insurance agent??

Did they remove the grout pocket from the outside and restress the cable with the splice? If so you are good to go. I work for a company that designs several thousand post tension slabs throughout the state and this happens often enough that the cable companies know how to handle it. Your cables probably came from Builders Post Tension(blue sheathing) and they are a good company. If they just spliced and didn't come back out and stress it's not going to do anything more than having a broken cable in there.

In regards to bonded vs. unbonded, you have unbonded. I'm not aware of any residential builders that use bonded and precast isn't really feasible for homes. Not really a good way to ship a 50' wide pre cast slab from a plant to a subdivision.

I am fairly certain that they did not re-tension from the end of the cable. My limited understanding is that the splice chuck has some way of tightening internally to provide tension.

It looks like our slab has these cables every 3 feet in both x and y directions. Haven't heard back from the foundation engineer as to the viability of the repair...

That's basically the same system we use to repair broken bridge beams. You'd be amazed how little room it takes to get it done. Pull up on the cable and if it feels taught, it was stressed and you can feel at ease. And no you don't go to the slab perimeter to restress because there's nothing to grab onto without pulling a whole new cable and good luck with that. I wouldn't beat the contractor up. He took care of it.

Thanks. The engineer who did our assessment a few years back got back to us and confirmed this is a common and reasonable repair too.

Seems now that since you have a trench running through your slab the PT cables really don't do much for you anymore (concerning the cables running across the trench). The whole point of the cables is to compress the concrete and now with that giant "kerf" in the slab, the tension forces are creating a folding effect on the slab and now have a lot higher chance of cracks to occur.

Think about holding a stack of books in front of you, lined horizontally. Without the compression from your arms squeezing the books together, they would just fall to the floor right? Now imagine inserting a book that is less that half the height of the rest of the books. The stack of books you are now compressing will want to fold upward since there is now a gap in the row of books. That folding effect is what your slab is now experiencing. The contractor just created a weak point in your slab.

The only way to 100% correct the issue would be to detension all cables spanning across trench, splice back the broken cable, hi-strength grout back the trench, and re-tension cables.

And yes, as stated above, that repair they did on your broken cable without retensioning did absolutely nothing for you. But if it was overengineered to accept that loss of compression force in the slab then it's all good. At least the broken cable was near the middle of your slab. If it was on the edge that would suck.

(Background: Post-Tension Institute Unbonded Installer certified)

Update: In your last picture it looks like they saw-cut full depth of slab since I see dirt. If that is the case, any cables that were passing through the trench will now want to suck in the two opposing edges of slab, and cracking would occur at the four corners of your trench.

Double back with your engineer....is he 100% that this repair is valid? At a minimum I would want to destress the exposed cables and restress after the trench has been grouted back.

Don't listen to this guy, he's like web md. Your slab is fine.