Thanks for your help. The cracks seem to be occuring most often when the native soil beneath the foundation stabilization material is fine sand. I now suspect that when the dewatering equipment is removed, the fine sand beneath the pipe is carried into the foundation stabilization rock beneath...
We are currently installing a 48-inch diameter sewer (Class IV RCP). The depth to flow line is 15 to 20 feet. Bedding for the pipe is 3/8-inch rock vibrated into place using "concrete stingers". Fill above the pipe zone is native material or import compacted to 90% of standard...
