CDFs affect on AC Water Pipe

[H2Otodrink]

We have had several instances where a contractor has used CDF to backfill between a deep sewer and a crossing shallow AC water main. This is only done occasionally to avoid large water shutdowns that would normally take place to splice in a section of ductile iron pipe at the crossings. Not long after we have been seeing the AC water pipe develop a circumferential crack on the bottom in the middle of the section that crosses the trench line. I'm trying to convince our City engineers that we should ALWAYS splice in the DI pipe when we have crossings as opposed to using CDF. I couldn't find any good arguments to support my theory so I'm seeking the guidance of experts here.

 

[cvg]

either
a) the CDF shrinks
b) the crack begins during temporary support before the CDF is placed and then gradually widens
c) both

I would require replacement with DIP or 11 month inspection to check for settlement / leakage before the contractor's warranty bond expires.