I have came accross two situations where conditions were like you describe. Both were solved with a concrete 'backfill'. I used a'Vermeer Wheel' trencher and rather then consume a lot of time cutting the old concrete and rock, the trench cut wasbackfilled with concrete slurry. I used Sch 80 PVC.
The site PE, and the inspectors had no issues, and no variations were required.
Edited by HotLine1 (12/04/13 06:59 PM)