A dramatic demonstration of frost heave

When we built our deck, we had to use a power auger to drill holes 3.5' into the ground under each footing and fill them with concrete. In the Chicagoland area the building code used to require just 3'. But the three bad winters we had at the end of the 1970s froze the ground deep enough that they added another half-foot to the required depth so that the bottom of the piles would be below the depth of the frost line. It turns out, it was pretty easy drilling 3' deep. But that extra half-foot was a pain. The soil kept dropping back into the hold. I finally used the shop vac to get enough dirt out to meet code. Note in Eric's photos below that it has pushed the old piles three or four feet out of the ground!

Eric Kurowski posted two photos with the comment:

Simple little deck bridge on the C&NW . This once was a small wood trestle. Was rebuilt a few times the Masonry of the big limestone blocks was original. The frost is pushing up the ORIGINAL piles in the middle that were once cut off below the waterline.Now this bridge has steel grates for deck and steel I beam for span replaces the wood timbers.

Dennis DeBruler I've heard of frost heave before. But I didn't realize that it could be so dramatic.

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All three of these videos talk about ice lenses forming in the soil. They are what creates an upward force, not the 10% expansion of water when it freezes. When water freezes, it drys out the soil below it. This dry soil sucks water in more water from the wetter soil below it with a wicking, i.e. capillary, action. This new water then freezes making the ice lens deeper. That again drys out the soil causing even more water to come join the party. So an ice lens will continue to grow and push the soil upwards as long as the temperature is below freezing and there is more water to pull out of the soil.

Ice lenses can form only in certain types of soil. If the soil is too porous, i.e. sand or gravel, it is well drained and doesn't hold the water long enough to freeze. If it is too impermeable, i.e. clay, it doesn't allow water to wick upwards and "feed" the ice lens. That explains why our building codes required a thick bed of gravel under our new concrete driveway.

Rocks conduct cold better than soil. So a rock will form an ice lens under itself. That explains why my grandfather had to pick rocks out of his farm fields year after year for many years.

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A video showing various machines to remove rocks from fields