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I live in Ontario, Canada, and the requirement for posts/bases is 4-feet deep in the ground, taking the frost line into consideration.

Now I saw this in Google images. I was just wondering if I can do this? Does the ENTIRE ditch need to be at least 4-feet deep? What will happen if the ditch is say, just 1-foot deep? Will the whole thing heave and crack/break during the winter cycle?

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    I think you have a slight misconception about how frost and heaving work. It's not the weight or strength of the concrete that prevent it heaving. It's the fact that the bottom of the concrete is so deep in the ground that the moisture in the ground below it doesn't freeze. The ground freezes very slowly from the surface downwards; that's why averagely colder climates have much deeper frost line. If your concrete stops 1' below the surface, the dirt underneath it will freeze and push it up a little bit. The dirt pushes inconsistently so there are weird stresses on the concrete.
    – Zach Mierzejewski
    Jul 21, 2016 at 17:52
  • Any reason you can't support each panel at the ends (on the frost-footing) and form an arch on the bottom at or slightly below grade? With suitable steel reinforcement (rebar) it should carry just fine.
    – isherwood
    Jul 21, 2016 at 18:08

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Best advice is to dig the whole thing down to the level below frost line. It is also the standard practice to put down a bed of gravel at the bottom and lay in a reinforced concrete footing that lies completely below the frost line and is wider that the fence support wall. Say 12 inches wide. This gives the poured wall structure something solid to sit on that does not heave and will also help mitigate problems with ground movement and settling.

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