Loading dock frost heave

[Ben29]

Would you be concerned about frost heave in this loading dock? The client wants to put a walk-in freezer on the loading dock (see highlighted corner of plan below). I raised concerns about frost heave since the one side of this slab is floating.

Their argument is that if the slab did heave, it would all move together, and the freezer would just move with it. I don't think this is the case. I think it is possible that the slab could crack and heave below the freezer, which would open up the joints between the insulation panels and render the freezer unusable. The proposed freezer is 4ft x 5ft.

 

[PEinc]

I don't think frost heave would be caused by the freezer sitting on the loading dock. If a freezer could cause frost heave, a freezer inside your house would cause the inside of the house to become cold. This does not happen. However, just like the other exterior footings for the building, the footings for the loading dock are exterior footings and should be founded below the local code-specified frost depth to prevent the footing from heaving due to extended, cold weather temperatures.

http://www.PeirceEngineering.com

 

[kissymoose]

I guess there weren't frost heave considerations for the original design either?

Response to PEinc - the freezer could be built directly on the slab without any floor framing or insulation, so the slab will be exposed to freezing temperatures just like if it were outside. Which it is and looks like it always has been, so if it's in an climate that experiences freezing and hasn't had problems so far, then you're probably in the clear.
Plus I'd expect an elevated volume of soil like that under the loading dock would drain water pretty well and therefore wouldn't be susceptible to heaving.

 

[Ben29]

I am not concerned that the freezer will cause frost heave. I am concerned that the slab could heave and damage the freezer.

 

[PEinc]

kissymoose, how efficient would a freezer be if it cooled down its outside surroundings? Not very. If the inside cold could get out, the outside heat could get in.
Ben29, I would consider two things: Is the soil under the new footing and under the new slab conducive to frost heave and what does the local building code require for frost protection depth of footings?

http://www.PeirceEngineering.com

 

[jhnblgr]

While the joint against the existing building wall is a place where water could infiltrate into below the surface it is unlikely a wall there cast with the slab would be better since water could still infiltrate the seam between the walls and push on both walls. Proper sealing between the joint is key. Is the loading dock sloping away from the building? The distance between the wall and the freezer is sufficient that a saw cut joint would prevent frost heaving the entire slab. But after how many years has it heaved yet? Design a steel skid for the freezer to sit on with leveling legs to ensure the structure can move as a unit without stressing the freezer.

 

[JAE]

Every freezer warehouse I've designed included underfloor heating to prevent soil frost heave.

The freezers base slab system was comprised of a 6" conc. "warehouse" slab, 10 inches of rigid insulation, a vapor barrier, 10 inches of drain gravel, and soil below.
The underfloor heat was set mid-height in the 10" rock.

Even with 10" of insulation, there were times, when the underfloor heat failed, that the ground froze and swelled up.

I can't see how a manufactured freezer is any different than this - there would be a temperature differential and possibility of soil freeze that I'd be concerned about.