this is for a watermain with a catchbasin in close proximity (2' away). 2" insulation board is being put between the structure and watermain as a precaution to prevent frost impact/freeze.
However, municipality has requested analysis of how long it will take for pipe to freeze. For simplicity I was going to calculate above ground. Water 40 degrees F, Air/Soil 0 degrees F. Main serves a decent number (200+/-)of homes and businesses so i'm assuming water will never be standing (or not for very long if it does). Hoping to prove it will take a min of 12 hours, which would be the max. it would go unused if no one uses their water overnight.
I take it that the water main is existing and CB would be new construction. Move the CB 2 to 3 feet along the curb and reinstall the curb to proper slope. In my opinion the water main should be much deeper if you get 0 degrees.
yes CB is new. Watermain is running parallel to the curb and the CB needs to be installed at the low point along the curb. Have already pushed the CB back and added a jog in the curb to get it away from the waterline the 2'. My question is would a 12" waterline serving that number of homes be at risk of freezing?
I would suggest that you present the insulating value of your insulating board in terms of equivalent feet of soil, and compare to the standard burial depth of the municipality.
A short answer to the R-Value of Dirt - about R 0.125 to R 0.25 per inch. Some sources researched assert that "one inch of 'insulation' is equal to about two feet or more of soil.
Your water pipe in air model is too far removed from reality. Also the idea that it could freeze almost solid overnight, then thaw open again is misguided. If it really lost significant cross-section to ice, the main couldn't provide needed fire flow at that time. Typical approaches discussed above-provide equivalent thermal protection as provided by ground cover. And the 1" insulation =2 feet soil agrees with our experience & thermal modelling.
