[This question follows one (https://www.askmehelpdesk.com/plumbing/gravel-clogged-sewage-pipe-lateral-how-what-do-about-212624.html) or two (https://www.askmehelpdesk.com/plumbing/standing-water-beneath-concrete-basement-floor-184273.html) related but earlier questions ]
New PVC pipes were put in the ground early October 2007, connecting to the old cast iron pipe (shown as ‘rust’ color in the schematic ). The pipes were laid in a freshly-dug area of the basement, stretching some 10’ x 12’ and about 18” deep at the deepest. No digging was done below the old cast iron pipe. In March 2008, our sewer backed up, and a video bore inspection of the sewer line showed that lots of gravel had entered the lines.
On 24 May 2008, we jack hammered up the concrete floor above the joint (above) and saw that the PVC pipe was cracked at the end of the “Y” joint where it meets the threaded Tee hub. The pipe had “sheared,” with the “Y” now 1” below the hub. (Image attached)
The most obvious cause of the crack is that the jackhammer slipped and the pipe cracked. But the guys who did the digging might deny that it broke during hammering.
Since we’re looking for a source of gravel infusion, I wonder if the pipe could have broken earlier beneath the concrete floor. Is it possible that the pipe broke while still buried, because it was not supported from below equally on both sides of the fracture? Here is a hypothetical scenario:
(1) After a half dozen heavy (3” - 6”) rains between October 2007 and March 2008, the freshly-dug and gravel-filled dirt floor (dubbed ‘lake basement’) below the PVC pipe “settled in.” The gravel, which initially supported the PVC pipe, began to sink as the ‘new’ dirt floor settled in.
(2) The old dirt floor, compacted over 50 years, does not sink.
(3) Stress resulting from the sinking of support on the new PVC causes the joint to shear fracture.
Thanks, ILS^2

the guys who did the digging might deny that it broke during hammering.
I think I agree with the cement guys and here's why,
In March 2008, our sewer backed up, and a video bore inspection of the sewer line showed that lots of gravel had entered the lines The line was opened up before they ever started to jackhammer.

Here is a hypothetical scenario:
(1) After a half dozen heavy (3” - 6”) rains between October 2007 and March 2008, the freshly-dug and gravel-filled dirt floor (dubbed 'lake basement') below the PVC pipe “settled in.” The gravel, which initially supported the PVC pipe, began to sink as the 'new' dirt floor settled in.
(2) The old dirt floor, compacted over 50 years, does not sink.
(3) Stress resulting from the sinking of support on the new PVC causes the joint to shear fracture.
I think ypu've done a great job of analyzing your problem and I also think you nailed it.
Redo the line and bed it in better this time. Good luck, Tom

Speedball1.
My contractor and his plumber don't believe my 'sinking dirt' hypothesis. They claim that digging then backfilling with the gravel they used should survive 'forever' and not sink and not cause pipes to shift and break. They claim that the procedure they use is the standard, even if it collects water time and time again. Do you have any evidence/facts that I can look up on the web that my 'sinking dirt' hypothesis has been shown true in a number of cases?
ILS^2

Your's is a unusual case. I haven't had any like it. Perhaps some of the other experts have run into it before.
However, the contractor's just got to to go on the defensive when you ask him how all the gravel got into the line if it wasn't broken before it was dug up. The way I see it, it was either a shoddy job of bedding the pipe or they laid the pipe with a strain on the joint and the joint cracked open allowing gravel to enter the line. Any way you slice and dice it all the doo-doo comes drizzling back down on them and they should foot the repair bill. Good luck and please keep me in the loop. Tom

Nothing but load from above or an impact breaks the pvc pipe like shown in the photo. Maybe shock from a nearby blast, but you would have other more obvious damage.

There could have been a void under the new pipe (mini sinkhole) to allow the pipe to settle and get some stone in it but breakage from settlement is impossible.

I am not a plumber, just an old roadbuildin', drainage pipe and compaction guy.

I got the original plumber to clean and fix the PVC pipe. He billed me $2755 to:
$1800 hydro-jetting service
$480 video service
$475 repair PVC drain line

He and the contractor are 'sure' that the guys who jack hammered up the concrete broke the PVC pipe then and there. They also believe that 'the other guys' were responsible for the gravel infiltration, but have no direct evidence. Nonetheless, the expect me to pay for the fix. [in addition to the $900 that the plumber charged me in march to video and snake out the gravel blockage.]

Questions you can or don't have to answer:
1. Are plumbing costs this high everywhere, or is the DC area particularly expensive?
2. why should I have to pay $3600+ for the fix?

I knew something nagged at the back of my mind when I first saw those pictures. In my area our inspectors insist on Purple Primer being used on all PVC joints so they could see that the joints have been properly primed before gluing. If primer isn't used, or the glaze removed by sanding it off the PVC will not weld together and make a solid joint. I don't see evidence of primer being used which makes me wounder if the joint didn't simply pull apart,( are the ends straight or jagged?) under the weight of therocks and cover.

He and the contractor are 'sure' that the guys who jack hammered up the concrete broke the PVC pipe then and there. They also believe that 'the other guys' were responsible for the gravel infiltration, but have no direct evidence. Well I'm not sure it wasn't a faulty installation to begain with. Let me know about the pipe end. Everything hinges on the pipe end. Did it really break or simply pull out under the weight of the cover or the force of the jackhammer because the joint was never prepared?

Questions you can or don't have to answer:
1. Are plumbing costs this high everywhere, or is the DC area particularly expensive?
2. why should I have to pay $3600+ for the fix?
We can't comment on labor or material costs without being on the job site ourselves. First to see what materials are needed, and second to access labor costs in your area, (union or non-union?) It's impossible for us to set here and estimate what a job would cost without seeing it. Sorry, Tom

I knew something nagged at the back of my mind when I first saw those pictures. In my area our inspectors insist on Purple Primer being used on all PVC joints so they could see that the joints have been properly primed before gluing. If primer isn't used, or the glaze removed by sanding it off the PVC will not weld together and make a solid joint. I don't see evidence of primer being used which makes me wounder if the joint didn't simply pull apart,( are the ends straight or jagged?) under the weight of the rocks and cover. . .

Yes, there was purple primer showing on the joining surfaces. I noticed it right away, then read on the web that it was necessary to use it. So that's not a contributor to the breakage.
ILS^2

The edges of the break look too clean to have been buried below concrete for any extended length of time. I'm thinking this likely happened when the concrete was being broken up.

I'm curious about the C/O Tee, though; Was this used as a test point to test the newly installed PVC piping?

Did they test it by filling it up with water?

If so, how much piping in linear feet are we talking about?

This is just a hunch, but I'm guessing they filled the entire system with a column of water, and that the gravel used as back fill in the ditch entered the cast iron portion of piping when they popped the test and the column of water came rushing out of the C/O Tee.

This is just a hunch, but I'm guessing they filled the entire system with a column of water, and that the gravel used as back fill in the ditch entered the cast iron portion of piping when they popped the test and the column of water came rushing out of the C/O Tee.
I think growler nailed it. A very logical explanation. Good analyzing growler. Tom