Use a 2" layer of the "compressible foam" that Roofers use Under Single Ply Membrane roofs that are directly applied to hard surfaces,usually referred to as "cushion board" by SPM Roofers,widen your footing either side if the pipe. Have used this methodology for frost heave, it works.
Has anyone checked the type of backfill that was used behind the wall,and the method that it was placed?? The moisture content of the material could create "bulking" of the soil if it is placed "dry" and then gets saturated.
