Frost Heave Calculation

[cduffy2232]

Hello All,

I am trying to determine the frost heave that will be experienced on a spread footing for pipe supports. I would like to use piles to be able to mitigate the issue of heave. However, the client would like us to use foundations above frost depth. I am trying to determine the heave on this foundation to assure the diesel fuel pipes running on the supports can withstand the movement. I have done some research but am unable to find a formula to calculate the heave that is practical. All of the formulas either require laboratory testing or are calculated in a completely controlled environment.

Any suggestions?

Thanks!

 

[fattdad]

I really don't know, but it seems you could undercut the foundation and install some open-graded aggregate that extends below the frost depth. Just make an engineered subbase of non-frost-susceptible aggregate and have your engineered footing rest on that subbase.

Then again, I really don't know. I don't like the sound of the structural engineer wanting to use piles but the non-engineering-client requesting something else - something more risky!

f-d

ípapß gordo ainÆt no madre flaca!

 

[oldestguy]

Frost heave calculation. An interesting subject, but full of variables. How's come my driveway heaved significantly the year after I moved in (8 year old house)? So when I mud jacked nearby settled slabs I "allowed for that heave" Well in the 8 added years I have been here sometimes no heave other times plenty. Same goes for roadways here in Wisconsin. I'd suggest lowering the grade say 6 inches, place 3 inches of closed cell Styrofoam, cover back up and be done with it. Extend this treatment out the "depth of freezing" which might be 2 feet and also might be 6, depending. Local contractors and grave diggers might be able to help on that number. Otherwise use 4 feet. Remembering the "column" sitting on that footing also is a heat conductor, so insulate it from the air and soil. Here in Wisconsin soil temp measurements I have made show freezing can be highly variable, depending a lot on soil type, being as deep as 8 feet when the code says 4 feet. Ya. The wetter the ground the shallower the freezing, as in a lake vs shore land. I'd use a shallow foundation, say 2 feet depth and extend the insulation out 4 feet from that footing edge.

 

[aeoliantexan]

You can Google "Modified Berggren Formula" and find a number of starting places. Berggren is also cited in "Principles of Pavement Design" by Yoder.

Frost heave can easily be several inches in northern states with frost-susceptible (silty) soils and a shallow water table or just poor drainage. On the other hand, dry, clean, sand or gravel may freeze without heaving. Heave can vary a lot from year to year depending on moisture conditions and weather.

Tell us about your soil type, water table, and approximate location.

 

[dlawrence529]

I view frost as an "infinite" force. If conditions are right for it to form, it can lift just about anything. I don't know of any calculation that will give frost pressure. I've seen published values of 10 tsf, but I believe they are based on back-calculating the pressure required to lift a building where frost heave was observed.

I think you'd have a couple options that are cheaper than driving pile. In general pile caps are placed below frost line anyway:

-remove and replace soil with non frost susceptible material (crushed stone) to the local frost depth.​

- there are insulation details for frost protected shallow foundations that use horizontal foam insulation boards (

http://msdssearch.dow.com/Published...oam/pdfs/noreg/178-04042.pdf&fromPage=GetDoc)

 

[oldestguy]

If you are going to replace "frost susceptible" soil with "non-frost susceptible soil", here are a few things to consider. Local "depth of frost" numbers are only possible depths, but a starting point. Frost susceptible soil,that is soil where frost lenses form readily, contain significant percentages of the silt fraction. That is at least 50 percent passing a Number 200 sieve yet exhibiting little plasticity as with cohesive clays. A simple rule of thumb is material with less than 10 percent passing a 200 sieve is OK for use to replace frost susceptible soil. How much depth to replace? The more water in that soil, the less the depth of freezing due to heat of fusion given off as ice forms. But, cleaner granular soils do not hold much water, so, even if they don't heave, the depth of freezing can go quite deep. Thus replacing frost susceptible soil with non frost susceptible soil means freezing depth goes deeper, possibly affecting that soil below the undercut. That may heave some, but due to the depth, the degree of heaving will be much less than the same site with no undercut replacement. So if the local word says frost depth is 4 feet, at least 4 feet of undercut replacement plus a "little more" might be about as good a rule as one can follow. The time honored rule of footing depth at 4 feet also can be followed, but not a guarantee of no heave, but don't backfill with clean sand since that poses little resistance to frost going down deeper, below the footing. Combine these possible treatment ways if one wishes. Finally remember frozen soil can grip a pile and tend to lift it if heave is present, so piles may heave under some circumstances..

 

[Okiryu]

cduffy2232, sorry do not want to hijack this thread... OG good points, question: for pavements with weak, non-expansive and frost-susceptible subgrade (elastic silts), we stabilize it with lime or cement-based. How the frost depth changes in this case?

 

[oldestguy]

dlawrence 529: I don't believe most of the diagrams presented by DOW in your attachment. If the schematic line depicting the boundary between frozen soil above and non frozen below goes only down and away off to the side, why project a layer of insulation out many feet from a foundation or other area to be protected? The cold condition (lack of heat energy) extending down past the end of the insulation will tend to go under, not only away from the insulation as well as vertically down. In other words since the actual movement of heat energy is from warm to cold, coming in from all uninsulated zones, in this case also coming partly from under the insulation. That's why you extend the insulation out a ways from the protected thing, in this case making the heat travel as long as possible, minimizing the cooling of the the parts well under projecting sheet. In those diagrams of no heave of the zone at the end of the insulated pavement, they should still show a heave at the end of the insulated pavement zone also.