The American Water Works Assoc has a tank design standard (AWWA D1OO-96) that has useful info about this topic. They have a US map with frost depths intended for use when setting the elevations of water lines into the tank.
They dig holes in the frost to fix water and sewer line breaks all the time. They have good first hand knowledge of how deep the frost can be in any area where they work.
Just add a safety factor to their amounts so that you are safe in an especially cold winter with little snow cover.
Rick Kitson MBA P.Eng
Construction Project Management
From conception to completion
You might try ASCE 7 or perhaps a foundation design handbook. I have seen maps of the US with frost depths drawn on it many places but cannot remember the source.
From an old mechanical engineer these charts are ultra conservative so I would not add a big safety margin. The frequency of actually getting the listed depth is about like a 100 year flood meaning you have to have a very cold winter, not much snow, etc.
dicksewerrat has it right, the local building code will be the controlling authority on footing depths, whether they use a local code or one of the model codes. However, when I want to know the current frost depth, I usually call the local cemetary. The grave diggers know the actual depth of frost at any given time - you might say it is part of their job desciption to know it! Their clientel are just dieing to know too. (Sorry, just couldn't pass that one up.)
Good one jheidt. The frost in the cemetary will mimic the frost in the yards of the area. The frost in the street(traveled portion)will be much greater.. that's when you call a few Sewer/water contractors. In Minnesota frost in the street can be 7-9 feet and the frost in the yard only 2-4 feet. Of course that depends a great deal on the snow depth and the way it fell.
You raise a point that I've always agreed with, but when it came up in a forum question a few months back, I took a lot of heat for, because I couldn't explain the actual mechanism. That is the fact that, frost is driven deeper under roadways than under open fields. Is there a practical, engineering explaination for this? Another example is under a temporary road in a construction site, the frost is driven deeper under the roadway than the adjacent soil areas.
I have believed that early snow covers reduce the depth of frost penetration by acting as a blanket of insulation. Not very scientific, but it seems to work that way in southern New England.
To answer the original post, you will have to determine what your finished grade is going to look like. If it is granular, ACP or concrete, frost will definitly penetrate deeper due to the poor (thermal resistance) R values of those materials.
However, one needs to understand the behavior of frost and how it migrates in order to provide remedial solutions.
Firstly, frost is NEVER driven down. The depth of penetration varies with the types of soils relative to the colder "degree" days. Frost penetrates because the soils "give up" heat. A depth of 7 to 9 feet is not uncommon under a road because the top two or three feet contain soils and structures that have very poor R values, like a metal frying pan versus a ceramic plate or asbestos, and readily lose any heat.
Frost moves like a cold plug. After 20 days of -20, this plug is considerably colder than 20 days of -10, and hence will penetrate deeper. In a cemetary for instance, where the soils are very fluffy and snow covered, the frost due to the high R values (insulation), do not readily give up their heat and frost does not migrate very far.
Lastly, and as anyone with northern utility experience will attest to, in a winter with many cold degree days and little precipitation followed by a warm spring, you will note that it now appears that the warmth is "driving" the frost down. Nope, what is occuring is the converse to the cold plug in that the soils, again due to poor R values, are now giving up the cold to the heat and warming quickly. However, the initial plug under the surface is still incredibly cold and continues to rob latent heat from the surrounding soils. Equilibrium is reached when the plug has warmed to the same temperature of the surrounding soils. That is the maximum depth of the frost.
I have studied frost and recorded several tempurature measurements of several soil types under several winter conditions. It is very interesting and predictable.
And it will be 80[°] F. here in San Antonio tomorrow -
Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"
and 100 plus here in West Bengal!! - 90+ at night. - and humid (very humid) - and not enough juice to run both aircons . . .)
One query - about local building codes giving the depth to footing levels. Doesn't the engineer have some control on the matter? Example - I had a job in a northern Ontario town - a very cold place and the depth of frost penetration was in the order of 9 to 10 ft. However, our soils investigation at the site gave us coarse grained sands (F1, I believe in the Navy frost susceptibility determination) and the water table in the "wet" season was down about 12 ft or so. So - why do we want to take the footings down to 10 ft - the soil on which the footing is sitting is non-frost susceptible! For sewers - it is different - you don't wan the liquids in the pipes freezing - has nothing to do with the soils frost susceptibility. KRS is right about the R factor analysis for depths actually achieved. Why thermodynamics, I suppose, was important!
You'll want to remember that building footing frost depths are not only based on how far down the frost goes. Frost heave on structures has a great deal to do with how the soil freezes to the exterior foundation wall and lifts up the building from the side.
While frost depths vary substantially based on who you ask and what kind of a year it is - footing frost depths are based on empirical methods (what has worked in the past). Industry standard for the building SEOR to get the frost depth goes something like this:
1) Check geotechnical report
2) Check with local code official
3) Check governing code
4) Check your opinion based on past experience and liturature
Any one of these options will work provided they are right
![[pacman]](/data/assets/smilies/pacman.gif "[pacman] [pacman]")
![[cheers]](/data/assets/smilies/cheers.gif "[cheers] [cheers]")
