Watermain under road with insificient cover

[PG35]

I have a watermain that has to pass over a very large storm pipe. The thermal cover will be 3'. 5' of cover is required in our area. Should pre-insulated pipe be used or should styrofoam sheets be used above the pipe? Both?

Thanks,
PG

 

[RWF7437]

You might also consider concrete encasement or "controlled density backfill" (a soil cement mixture) either of which would add structural strength.

good luck

 

[CarlB]

If there will always be plenty of flow in the main you might not really need either. But to achieve the lacking 2' of thermal (earth) cover, 2" thick insulation (board/sheet) would be enough. But you need to extend it probably 4' or so each side of pipe. And, there could be a concern the storm drain line would have freezing temperatures, with frozen soil forming around it (well probably not unless it was a short culvert, but some agencies tend to regard them as a "cold" source). A possible side effect from shallow sheet insulation under a road is that it can cause icing on the road surface, as it can be a "cold" spot with less heat rising from below. Given the above, I would recommend pre-insulated piping with 2"-3" annular insualtion. No additional sheet insulation.