Learned why frost heave wrecks posts in North Dakota, wish I knew sooner

I was out near Minot last month on a job and the homeowner's old posts were all pushed up a good 3 inches. I always blamed bad concrete but he showed me the soil test from his county extension office. Turns out the type of clay up there holds water like crazy and freezes from the top down, so the ground literally lifts the whole footing. I checked the frost depth map for that area, it's 60 inches, so a standard 36 inch hole is nowhere near enough without gravel drainage. Has anyone else run into soils that need special footings and just dug deeper instead of changing the mix?

2 comments

2 Comments

kim_davis4d ago

That 60 inch frost line explains a lot, I pulled a few posts near Devils Lake that had 48 inch holes and they still moved. Swapping to a gravel collar and wrapping the top of the concrete with foam insulation fixed it on the last two jobs.

miaprice2d ago

Noticing how frost heave works on fence posts kinda makes you see it everywhere, sidewalks, driveways, even those little utility poles by the road... it's all the same battle with the ground moving under us.