Frost Depth for Static Fire Line

[akastud]

Dear all, forgive me for being ignorant in this community, but I am a Structural Engineer and I am in the process of building a building for my buisness. The contractor has found an extremely large vault in the path of my Fire Sprinler Supply that the city does not show in any as builts. The top of the vault is at 36" below the pavement and according to the fire officials in town the pipe has to have 36" of cover so my 4" pipe only has 32" of cover. Frost depth for everything else in my area is 30" but the fire guys say this is a static line that frost depth is deeper. The vault is 12' tall and runs through our entire frontage. The contractor says if he has to go under the vault it will be a mighty change order. Is there any approved way to insulate the pipe at a 32" cover? Also realize that this is under a road so it would have to be some kind of rigid system. Can anyone help me?

akastud

 

[safetydan]

One way you can get around the 36" of cover is to add 4" of fill over the line on the day of installation. Most depth codes say the lines have to be so many inches below the surface on the day of installation. What happens after the day of installation (errosion, excavation, etc.) isn't covered in standards.

 

[akastud]

The problem it is in the street. I don't think they will let us leave a 4" bump in the street.

David S. Merrell, P.E.
TOR Engineering

http://www.TOREngineering.com

 

[cdafd]

So if you to run up to near the vault at the 36 inch or deeper mark and than angle up to go over the vault how much line would actualy be at 36 inches or less???

 

[cdafd]

10.4 Depth of Cover.
10.4.1* The depth of cover over water pipes shall be determined by the maximum depth of frost penetration in the locality where the pipe is laid.
10.4.2 The top of the pipe shall be buried not less than 1 ft (0.3 m) below the frost line for the locality.
10.4.3 In those locations where frost is not a factor, the depth of cover shall be not less than 2½ ft (0.8 m) to prevent mechanical damage.
10.4.4 Pipe under driveways shall be buried at a minimum depth of 3 ft (0.9 m).
10.4.5 Pipe under railroad tracks shall be buried at a minimum depth of 4 ft (1.2 m).
10.4.6 The depth of cover shall be measured from the top of the pipe to finished grade, and due consideration shall always be given to future or final grade and nature of soil.



10.5 Protection Against Freezing.
10.5.1* Where it is impracticable to bury pipe, pipe shall be permitted to be laid aboveground, provided that the pipe is protected against freezing and mechanical damage.
10.5.2 Pipe shall be buried below the frost line where entering streams and other bodies of water.
10.5.3 Where pipe is laid in water raceways or shallow streams, care shall be taken that there will be sufficient depth of running water between the pipe and the frost line during all seasons of frost; a safer method is to bury the pipe 1 ft (0.3048 m) or more under the bed of the waterway.
10.5.4 Pipe shall be located at a distance from stream banks and embankment walls that prevents danger of freezing through the side of the bank.


kinda looks like you have a problem also t=in that it is suppose to be 36 inches under a driveway

 

[akastud]

Yeah, and it says 1' below the frost line. Our frost line is actually 30" so really it should be at 42"

David S. Merrell, P.E.
TOR Engineering

http://www.TOREngineering.com

 

[akastud]

cdafd, it will be at 32" below grade for 3' max, and then at 36" on both sides.

David S. Merrell, P.E.
TOR Engineering

http://www.TOREngineering.com

 

[TravisMack]

If I am correct, you are in Flag AZ with this new building. Per the tables in NFPA 13, you need to have between 42" and 48" of bury. If you are sure that your frost line is 30", then you need to have a minimum of 42" of bury.

 

[CarlB]

In cold regions insulation is commonly used to substitute for earth cover when water lines need to be placed shallower than the frost depth. And some lines (with annular insulation, circulating and heat traced) are placed in permafrost; lines would have to go 300 feet in places to get below it! If mechanical issues are addressed, I would say 2" thick rigid insulation (extruded polystyrene by DOW or similar), 4 feet wide, placed a few inches over the pipe, will be quivalent to a few feet of earth cover for thermal protection. And the vault top probably is "warmer" than similar soil at 3' during cold periods, as it brings in heat from a greater depth.