Insulation under culvert?

[SMIAH]

I recently had to debate with a technician about insulation of culvert.

From my perspective, we try to put styrofoam above (horizontal) or as an inverted U around the pipe when we know that we're near the depth of penetration of frost.
The technician says that they only put styrofoam under the culvert to prevent the frost in the culvert to get to the bedding.

I'd like to hear what you guys think about this? I think this could depend on the fact that there is water flowing (or not) in the culvert.

Just to mention that we're in 2500 F-days design freezing index.

 

[gbam]

Interesting topic, being located in southern Arizona we never deal with this. I will be watching this thread.

 

[LincolnPE]

For waterlines we put blue board over, but culverts are exposed to air and freeze.

 

[civilman72]

What Lincoln said. I've never seen a culvert/storm sewer insulated. The air in the pipe will cause the water inside to freeze much sooner than the frost in soil around it. In fact during the winter the air temperature in the pipe is probably lower than the adjacent soil.

Not sure why protecting the bedding from freezing below the pipe is important. There may be some benefit, but I would be more concerned with potential settling issues with placing styrofoam under a culvert.