Replies

1. 
   DanH | May 15, 2014 06:37pm | #1

   Mainly, remove even more expansive soil, and provide good drainage.

2. 
   AndyEngel | May 16, 2014 02:36pm | #2

   Foam below?

   Sounds like a frost protected shallow footing, in essence. There's an ASCE document on them for use in unheated buildings, and I would think that would work as well for sidewalks. I've built two buildings on such footings. I'm in the same ag zone as you are, so the requirements would be similar. For a foundation, you'd need min. 6 inches of clean stone followed with at least 2 inches of foam under the concrete. The foam would have to extend out about 4 feet on each side of the concrete, and have a foot of soil above, so you end up with deeper stone or a haunched subgrade. That's a bunch for a sidewalk, but I doubt just having foam directly below the walk would do enough. So, I'd go for 6 inches of stone with the grade below sloped for drainage and compacted. You might need to go so far as to pipe away the water.

1. 
   DanH | May 16, 2014 05:46pm | #3

   You can solve the width problem somewhat by going deep instead.  Come out 6-12 inches beyond the concrete with the foam, then dig down a foot or three and install a vertical piece.  The idea is to "capture" all the heat rising from below, not allowing any of it to escape to the sides.

   But for the effort required I'd rather just add another 6-12 inches of non-expansive fill.  It's a sidewalk, not the Taj Mahal.

1. 
   AndyEngel | May 20, 2014 09:57am | #4

   Agreed. The OP mentioned foam, which is why I mentioned it. Drainage and granular fill can also prevent heave, and probably at a lower cost.