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Frost Uplift in Granular Soils with shallow phreatic level

Frost Uplift in Granular Soils with shallow phreatic level

Frost Uplift in Granular Soils with shallow phreatic level

(OP)
Hi to all of you,
I’m currently working in a project where extremely low temperatures are reached in winter and can occasionate frost heave.

The soil is granular with few clay and silt particles (theoretically no problem), but phreatic level is between 1-2.5ft depth, while frost depth is about 2ft.

I’m not quite sure about if foundations will be subjected to frost heave in such conditions, which scenario is worst (phreatic level at 1ft or at 2.5ft) and how will act the soil in such conditions.

Has anyone faced something similar or can you recommend me any specific publication about that?
I have been making a research and I couldn’t find data for such specific case. Can you help me with this?

Thank you!

RE: Frost Uplift in Granular Soils with shallow phreatic level

I don't deal with frost at all in my part of the world.

I did however deal with a case where seepage infiltrated beneath the floor slabs of a poorly insulated cold storage room and froze- despite the soils being generally sandy, with some silt and clay present, the ensuing heave was considerable and led to the slabs having to be broken out completely and replaced.

Wait for the frost experts- but I would be very cautious with your foundation design. A little detail on the type of structures you're dealing with could add context for specific recommendations.

All the best,
Mike

RE: Frost Uplift in Granular Soils with shallow phreatic level

Don't get tied to "frost depth" as meaning anything. In your case, the water table is shallow. Go to a lake and measure the thickness of ice on a lake there. That's one "frost depth". Then go to where the water table is low and same soils as your site. Likely very deep freezing. It all is controlled by water. So at your site with low silt content about the only heaving would be whatever volume change there is between unfrozen water and frozen water in a water thickness about like that lake. With insulation on the surface, maybe less thickness of freezing of the water zone.

RE: Frost Uplift in Granular Soils with shallow phreatic level

I might add to the situation. Noting that ground water in soil cannot occupy all the volume at any one cubic foot, depth of freezing temp then can go deeper in that saturated zone as compared to a cubic foot of water in the lake. Then this old guy will relate something that opened my eyes once. I was called to a place where there had been a fire caused by a gas main contracting when cold and opening a welded joint, feeding gas into a building causing an explosion. This was the week between Christmas and New Years, La Crosse Wisconsin, a deep sand area, deep water table. I did a hand auger boring below a sidewalk nearby, measuring temps as depth went down. It was below freezing 8 feet below the sidewalk in clean sand, of very low moisture content. So there the so called "frost depth" was very deep.

RE: Frost Uplift in Granular Soils with shallow phreatic level

The U.S. Corps of Engineers classifies any non-organic soil with more than 3 percent finer than 0.02 mm as frost-susceptible. Highly frost-susceptible soils usually have a significant silt content, providing high capillarity to move water to the freezing front and sufficient permeability to let considerable water migrate and form frost lenses in one cold season.

I would be cautious of your situation. With the water table so shallow, not much capillarity is needed. Liquid water migrates to frozen water, and ice lenses may form. Also, even if lenses do not form and the water just freezes in place, it expands about 10 percent going from liquid to solid. The soil is about 1/3rd to 1/2 water by volume, so it will expand about 3 to 5 percent.

I suggest asking the locals what minimum footing depth is customary, then going a little deeper.

Can you tell us the general location?

RE: Frost Uplift in Granular Soils with shallow phreatic level

(OP)
Thank you for the answers, it's a "new" issue for me because usually this kind of phenomena is neither present where I am.

@Mad Mike thank you for explaining that case, I think its very interesting how a soil that theoretically is not propense to frost heave can generate such effects, I will have that in consideration.

@Oldestguy, I agree with you in using the water depth frozen in a lake or river near the zone, but not quite sure about if this information will be useful at all for me. I need to provide a guarantee for such structure for a long period of time, and if I take such measurement next winter (for example) who tells me that this will be the coldest one?? Maybe this year winter is warmer than normally, so to have an idea I think it's okay, but not to base calculations or frost depth on that. If i can find a register about this, then I will use it!

@aeoliantexan Yes, i'm conscious about the hazards of the ice and agree with you that maybe the best will be to ask to local contractors.

The project is located in country with average temperatures below 0 during 3-4 months of the year and initially the intention is to use steel piles for foundation.. will see what to do with this problem..

RE: Frost Uplift in Granular Soils with shallow phreatic level

Is your temperature of zero Fahrenheit or Celsius? It makes a big difference as to frost action. Play it safe and set foundations below the frozen depth. It may take some dewatering to do that. Simple pumping from pits can loosen soil below the pit. I'd look to pits off to the side of the foundation or well points. Many a settlement problem can be created by improper dewatering. This is assuming you know that "frost depth" as meaning anything.

RE: Frost Uplift in Granular Soils with shallow phreatic level

>The soil is granular with few clay and silt particles (theoretically no problem),

How many is 'few'? Because you can go from 'no frost heave problem' at 5% fines to 'worst case scenario frost heave' at ~20% or so.

Hypothetically if it was 0% fines all you would have is some volume change from the water expanding.

RE: Frost Uplift in Granular Soils with shallow phreatic level

(OP)
Obviously is not clean at all. Few is around 10%.

But let's suppose that is as you said hypothetically 0%. Agree with you in that all the expansion that will appear will be a consequence of the volume change of the water.

Should I consider that as worst condition? How can I calculate the uplift of the structure? Not sure at all about this point if soil won't experiment a change in volume.

For me, in that hypothetical case with no fine grained, the situation should be similar as pile foundation over a lake that during winter freezes. However, when this happen, are piles uplift? This is not my field so if anyone can help me I will appreciate!


Oldestguy, temperature is in Celsius, in Fahrenheit would be extreme climate and probably permafrost would remain at shallow depths during the whole year, so this problem wouldn't appear.

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