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18" Dia. x 42" Sonotube ?

In climates where the ground freezes you would have big problems if you poured against the earth. The irregular surfaces allow the freezing soil to grab the pier and heave it out of the ground. Also, those piers are not designed for any lateral loading since they support gravity loads only; a void would not affect performance. For something to move, you need a force to move it. (F-ma, a=F/m)
We've seen this issue quite a bit even with the formed sonotube. The issue was that there was no spread footing underneath the sonotube to prevent the frost from lifting the concrete column out of the ground. My understanding is this phenomena is more related to the particle size of the soil being suitable for capillary force than it is the shape of the foundation, but I am just going off of what our local engineers have told me about the issue.
 
We've seen this issue quite a bit even with the formed sonotube. The issue was that there was no spread footing underneath the sonotube to prevent the frost from lifting the concrete column out of the ground. My understanding is this phenomena is more related to the particle size of the soil being suitable for capillary force than it is the shape of the foundation, but I am just going off of what our local engineers have told me about the issue.
A spread base would help but not required by code or engineering for a deck. The soil type is definitely a significant factor. Clays grab and heave white granular does neither. I do specify that shallow sonotube type pier foundations are formed and must not be cast against earth on the sides on sites that experience ground freezing.
 
Interesting. It is required in the Canadian building code.

There must be different soil on the other side your state's border with Ontario and Manitoba. :p
Where is it required in the code? Often the sonotube is sized for the bearing area required, not the strength of the pier. If I need 250 sq in of bearing area I can simply use an 18" pier. Maybe the Canadian code requires you to enlarge the base of a pier foundation but I can't think of a reason for that provision unless there is net uplift. I can't see how that would ever be the prescriptive case with decks.
 
Where is it required in the code? Often the sonotube is sized for the bearing area required, not the strength of the pier. If I need 250 sq in of bearing area I can simply use an 18" pier. Maybe the Canadian code requires you to enlarge the base of a pier foundation but I can't think of a reason for that provision unless there is net uplift. I can't see how that would ever be the prescriptive case with decks.
Table 9.15.3.4

Minimum column pad in Canada is .4 square meters (620 sq. in.), unless engineering is provided and I have not had anyone go that route, even engineers designs for their own homes (they have a tendency to go a little overboard). I've only seen 18" concrete tubes used in commercial construction. Even there, we see them on large formed footings. When I say I've never seen someone use a sonotube without a column pad under it, I mean anywhere. Commercial, residential, it doesn't matter. I've never seen it.

Most people will use a 8-10" dia. tube for a residential deck here to reduce the cost of concrete.
 
Table 9.15.3.4

Minimum column pad in Canada is .4 square meters (620 sq. in.), unless engineering is provided and I have not had anyone go that route, even engineers designs for their own homes (they have a tendency to go a little overboard). I've only seen 18" concrete tubes used in commercial construction. Even there, we see them on large formed footings. When I say I've never seen someone use a sonotube without a column pad under it, I mean anywhere. Commercial, residential, it doesn't matter. I've never seen it.

Most people will use a 8-10" dia. tube for a residential deck here to reduce the cost of concrete.

9.15.3.1. Footings Required​

1) Intent StatementFootings shall be provided under walls, pilasters, columns, piers, fireplaces and chimneys that bear on soil or rock, except that footings may be omitted under piers or monolithic concrete walls if the safe loadbearing capacity of the soil or rock is not exceeded.
 

9.15.3.1. Footings Required​

1) Intent StatementFootings shall be provided under walls, pilasters, columns, piers, fireplaces and chimneys that bear on soil or rock, except that footings may be omitted under piers or monolithic concrete walls if the safe loadbearing capacity of the soil or rock is not exceeded.
Yup. So they can either install $100 worth of concrete and pads or do a $2,000 subsurface investigation (see 4.2.4.2. and Div. A 1.4.1.2. definition of subsurface investigation). Again, even with geotechnical reviews of the soils on larger projects, we still see column pads under concrete columns.
 
Yup. So they can either install $100 worth of concrete and pads or do a $2,000 subsurface investigation (see 4.2.4.2. and Div. A 1.4.1.2. definition of subsurface investigation). Again, even with geotechnical reviews of the soils on larger projects, we still see column pads under concrete columns.
You also have prescriptive allowable soil bearing pressures which are the values typically used in residential decks and additions.
 
You also have prescriptive allowable soil bearing pressures which are the values typically used in residential decks and additions.
You're right. 75 kPa, so the applicant would now need to hire an engineer to perform the calculations under Part 4 of the code. So, a much improved $750-$1,500 to save $100.
 
Difference between bearing and friction resistance no? If soil is subject to seasonal heaving wouldn't belling the bottoms of the footings be a better solution.
Note that a future owner might enclose the deck leading to greater loads.
 
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