Hello, I have dug down 4 feet in clay soil and inserted 8 inch sone tubes to make piers for a deck project. SHould I fill in the hole around the sonetube with sand, crushed gravel, gravel, or original clay soil?
If your down 4 ft back filling with the clay will be fine. Back filling with gravel or while not a bad idea probably wont stay effective very long. The particles from the clay will fill the voids in the gravel. Sand has smaller voids in it so would be effective long as drainage.
I would suggest using road crush because it packs tight (pack it with a shovel handle or similar as you back fill the hole a few inches at a time) and it retains less moisture than soil and clay; therefore it will heave less when the frost gets at it. Good luck on the project!
If you have lots of room around the sonotube, I would use a road crush (sand and gravel mix) and use that in layers...add about 6 inches and tamp it down firm until you have filled all the way to grade.
This will give you excellent drainage around the piling.
We back fill any space with the original soil.
Adding gravel to the outside of the Sonotube will allow water to fill the hole and crack the pillar when the frost hits.
Make sure you have at least 6" of concrete and tube above grade, according to code!
Hope this helps.
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