Shallow foundation design in cold climates 1

[gamecockPE]

Hi,

I have a project in Wyoming where five separate concrete footings supporting a rock conveyor will be installed. The purposed footing depth is currently only 12", which surprised me at first, as the county normally requires 36". After some digging through IBC 2009, I found section 1809.5 on frost protection. This section lists three conditions that must be met in order for buildings or structures to be exemption from frost protection requirements. They are as follows (not verbatim): free-standing buildings or structures assigned in occupancy category I (agricultural buildings, etc.), area of 600 sq ft or less for light-frame construction, eave height of 10 feet or less.
It appears that my project would meet all three of these conditions, permitting 12" footings.
My question is, would it be a bad idea to pour these separate footings, supporting the same conveyor, at a depth of 12"? My concern is if one footing rose 2" and another didn't, for instance. Perhaps this could cause my conveyor to lean? I have no idea what the true magnitude of frost heave for small footings could be (approx.. 8'x8').

Additionally, this article gave me more to think about:
Frost Protected Shallow Foundations

http://buildipedia.com/aec-pros/con...nd-why-of-frost-protected-shallow-foundations

I imagine its a slightly different when you can consider heat from a home or building on top of your foundation, however ASCE 32 (which I don't have a copy of at the moment) eludes to techniques for foundations for non-heated structures (i.e. garages).

Thank you in advance for your insight!

 

[oldestguy]

A couple of questions. What type of soil will the pas sit on? If of low frost susceptibility, no problem. Second question. Is the conveyor supplied by a manufacturer that has some guidelines on what differential settlement can be tolerated? I'd suspect the conveyor is very tolerant of differential settlement (or heaving).

Many a temporary quarry operation has the gear setting on timber grillage, generally not a problem.

 

[gamecockPE]

Unfortunately, I wasn't able to get any more information regarding the existing soil. Nor did I hear of any settlement tolerances for the conveyor equipment from my project engineer.
Apparently, there is an adjacent foundation there now that is approx. 24" deep, with no history of heave. Sounds like everyone involved would rather just match existing and move on without applying any more thought to the matter.
Given the small difference of concrete we could potentially save, I won't object to this either.

Thanks again for your help. I will keep in mind soil type for next time this issue comes up.

Best Regards,