Dealing with a severed post tension cable in the slab

I had a similar nightmare when we were installing a floor safe in my 1990s-built ranch. We actualy hired a scanning company, but they missed a cable tucked deeper in the slab near the master closet. When that strand snapped, it sounded like a literal gunshot; the force actually cracked a few of my existing tiles three feet away. We saw that same red grease and plastic casing sticking out from the cut.

My engineer had me use PTI-certified technicians for the repair rather than letting the general contractor handle it. We had to chip out about a three-foot pocket to get enought slack for a coupler. They used a specialized hydraulic ram to re-tension it to about 33,000 psi. It was an expensive $1,800 detour, but after seeing how much energy is stored in those 0.5-inch strands, I wouldn't trust a standard patch job. Make sure you get the tensioning report for your records, as it's a huge deal for resale value later on.

When I ran into this during a kitchen expansion, the "snap" was surprisingly quiet, more like a dull thud. My GC actualy tried to convince me that the cable wasn't under high tension becuase the slab was over twenty years old. I didn't buy it. I ended up calling a local PT specialist who used a hydraulic jack to check the remaining lift on the cable. It turned out the strand had lost nearly 25 kips of force, wich is terrifying when you realize that’s what’s holding your foundation's compression together.

The fix was more invasive than I expected. Instead of just patching it, they had to use a "barrel and wedge" coupler to splice the broken ends back together. We had to chip out a pocket about 3 feet long and 8 inches wide just to get the equipment in there. If you're going trough this, make sure they actually use a calibrated gauge when they re-tension it. Just "tightening it up" doesn't count. We ended up paying about $1,800 just for the repair and the certified report for our records, which was a huge hit to our contingency budget.

Have you ruled out that the "snap" was just the concrete spalling off as the drill bit hit the steel, rather than the cable actualy letting go under tension? I’ve seen guys jump at any loud noise in a renovation, but if the slab didn't actually heave or show a new surface crack, it might not have been a live tendon. Are you 100% sure that wasn't an abandoned run or just a weirdly placed piece of conduit? Sometimes that red plastic sheathing is used for other utilities depending on who did the original pour. I’d want to see the actual wedges at the anchor before I paid for a full re-tensioning job.