Identify this PVC drain pipe fault!

[OkieFish]

If anyone can tell me what might have caused the hole in this drain pipe, I would LOVE to hear it! Pls see attached photo.

Background: this section of drain line is installed under a kitchen sink. We started getting a leak around the floor and narrowed it down to water coming up out of foundation at the point where drain line enters it when the washing machine and dishwasher were running at same time; that + a grease-narrowed main line caused water to back up to the bottom of the sink line. We just paid $4K for tunnel under slab repair.

There had been a previous repair job of some type in the area, as the foundation had been busted thru and poorly repatched where the sink drain line enters the slab. I just wondered if anyone had ever seen this type of a hole in pvc drain line in this application. I have an idea, but would like to see what the pros say.
Thanks

 

[Mr_David]

There had been a previous repair job of some type in the area

You said it right there?
Probably during previous work, they hit it with their chipping hammer and said "OOPS ! Bury it! Can't see it from my house."

I have done an oops or 2 in my day. But I didn't leave them like that.

Was there copper water lines in the slab. maybe they were fixing a water line in the slab.