Tom
The original service to my garage was run in that black poly pipe. It lasted quite awhile, as it was probably put in 1978. It was only about 6"-8" deep, and finally one winter I caught the pipe with the corner of the plow, at the corner of the garage.
I learned two things that night.
I had always wondered how they got the service up into the garage. It came up in the middle of the bottom plate. I found out that it had been carefully woven and pressed into the stones and aggregate on the edge of the slab pour, and had been concealed with mortar. It was actually quite clever.
2nd thing I learned was that the breaker didn't trip, like it should have. It was a little sparkly out there for a few seconds.