Frost protection of foundations
Frost protection of foundations
(OP)
Is there any other methods or reason that we can arguee that it is okay not have the foundation to frost depth?
Does an equipment pad located outdoor needs to go to the frost depth?
In what cases we can go above the frost depth?
Thank you
Does an equipment pad located outdoor needs to go to the frost depth?
In what cases we can go above the frost depth?
Thank you






RE: Frost protection of foundations
I wouldn't use this method if the equipment on top was sensitive to movement. This method reduces frost heave but doesn't eliminate it.
RE: Frost protection of foundations
RE: Frost protection of foundations
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If it's a mission critical application, I'll usually solicit recommendations from a local geotechnical engineer.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Frost protection of foundations
I've worked in a lot of northern canadian industrial sites where it's impractical to always build to frost and the amount of insulation and distance you have to carry it past the edge of footing sometimes makes things impossible.
If you've got an electrical cabinet where you can build some slack into the cable, it's silly to build a footing two or three meters into the ground. Same for small scale equipment that could take some degree of movement and isn't process critical.
Alternatively, you can look at the history of the site. Not all soils are frost susceptible and not all water tables are in a position to cause problems. You can quantify that, to some degree, but you can also examine the site. If you have pavement nearby that's been in place for a decade, you can take a look for instances of frost heave. Maybe you have well draining soil and are near the edge of a hill, or have a deep drainage channel nearby that would keep a high water table from forming. You can also look at detailing of existing structures on the site. If they have shallow equipment foundations and they work adequately, you may be fine.If you aren't comfortable doing that, find a geotech that is.
In all of these cases, you should explain the risk-benefit situation to the client.
"Standard practice is <something>, the cost of doing it this way is <lots>, you may be able to do <something cheaper> because of <reasons>. There is a <negligible/small/medium/significant> risk of <something bad happening. I recommend <blah>."
As long as it's not a life safety issue and you have a somewhat sophisticated client with the ability to understand the consequences to their equipment, then there's no issue with approaching from this direction. Just make sure that you document the basis of your design.
RE: Frost protection of foundations
Mike McCann, PE, SE (WA)
RE: Frost protection of foundations
RE: Frost protection of foundations
I have seen frost heave lift buildings several inches over decades. The ice lifts, fines fill the voids, the building repeats the process next winter.
RE: Frost protection of foundations
I've never seen a real basis for the argument that traffic impact drives frost deeper. It doesn't seem to make any sense, and the only actual writing I've ever seen on it is people disagreeing with it. There are all sorts of reasons why frost depth would vary on roadways (cleared of insulating organics, generally kept clear of snow, different fill materials, etc), but I don't think impact driving frost deeper is one of them.
RE: Frost protection of foundations
Thank you very much for your responses.
Great information.
Just was wondering when using rigid insulation how much it reduces the frost depth?
Let's say for regular 4ft frost depth area, does it depend on the foundation size and thickness?
Thank you
RE: Frost protection of foundations
However, that is strictly a very conservative rule of thumb and as many others above have noted, it does not necessarily apply to all areas or applications.
RE: Frost protection of foundations
Traffic does send the frost deeper. I dug up 1,000's of feet of trench in MPLS. Frost depth in busy roads, normal winter 5-7 feet, residential roads 46 feet in the yards adjacent to both roads, 2-3 feet. And yes when I was there we installed and repaired sewer pipes all winter.
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Frost protection of foundations
I can't see a mechanism by which smacking something would move heat. If I stick a steel rod in the fire and then smack it against the ground a bunch, the heat's not going to transmit any faster than if I just left it alone. You also aren't physically driving particles deeper with traffic, or you'd also be having huge settlement problems.
Minnesota MOT does a huge amount of frost related research and none of the formulas I've seen in their papers take into account the amount of traffic on the roads. They have lots of experimental data and if they saw correlations between frost depth and the amount of traffic they'd take advantage of it.
You can also see that snow cover makes a big difference:
http://downloads.geo-slope.com/geostudioresources/...
RE: Frost protection of foundations
These all can be assigned some mechanism that makes sense, maybe. Impact doesn't, especially way down there.
RE: Frost protection of foundations
RE: Frost protection of foundations
The lack of cover also drives energy loss due to convection. You can stay warm in the sun on a still cold day if you're not moving. However, once the wind blows, the transfer of energy increases significantly. Like a lawn, hair on your body can help to mitigate that. But like pavement, a bald head chills quite readily with the wind blowing over it.
Finally, there is the loss of heat through radiation on those crisp clear nights. Exposed to the absolute zero darkness of the sky, the pavement will give up it's energy quite readily. That's the very reason we get frost and/or black ice in situations when the air temperature is still above freezing.
All of these things serve to drive the ice deep into the unprotected ground. At least as I understand it anyway.