clay soil 8 inch sonotube hole fill in?

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Posted by: from Ottawa
6/25/2018 at 8:40:13 PM

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?



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Date/Time6/25/2018 at 9:22:48 PM

Sonotube should be filled with concrete

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Date/Time6/25/2018 at 9:40:35 PM

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.

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Date/Time6/25/2018 at 9:46:51 PM

Hey Bill, I hate to be the bearer of bad news but 8 sonotubes no longer meet code for a deck, also, 60 below grade is required for Ottawa, not the typical 48 , but double check with building department.

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Date/Time6/25/2018 at 9:48:00 PM

Also, it's fine to backfill with the soil you removed for the footing

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Date/Time6/25/2018 at 11:37:07 PM

Hey there.

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!

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Date/Time6/26/2018 at 1:29:42 AM

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.

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Brandon from MBM ConScapes in Bradford
Date/Time6/26/2018 at 3:39:33 PM

Hi William,

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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