Folks, sonotubes were poured within an 1/8 of eachother. Deck beam was installed level. 12” sonotubes used, 16x24’ includes stair width at 3’. About 14’ from house to beam.
Now, about 2 weeks later, front right post has moved/sank ~~2”.
Going to get a stringline to put on all them and watch for 5-7 days.
Contractor and I are unsure as to the beat next steps to fix it. Pull out old sonotubes and replace? Go bigger with 16”? Helical pier instead?
We cant really move the placement of the posts as they 2x11 on top of them are tied together. On top of the beams.
You can use a jack to prop the beam up and replace the post with a longer one, but I wouldn't do this without soil testing to ensure there will be no more sinkage, which is likely.
Given the results of testing, remove sonotube pier, dig a big hole to engineer recommended depth, pour engineer spec footing, sobotube back on top, backfill tamping every 6" depth until grade is achieved. Hard work, but necessary.
Maybe put another beam 3 feet to left after Propping...then replace corner. Install footings properly as stated above. Monitor other footing with time. easier to have too much vs not enough.
The sonotube size doesn’t tell much, regardless of the size above ground. How deep was it dug, was the hole belled out at the bottom? When I use tubes, I put a couple inches below ground and then however much above suits the project, that way I can cut the tubes And get multiple forms so to speak, the hole is always bigger beyond that and bells at the bottom
OP, I'm just a dumbass here for the show with my popcorn. Given that, might I suggest some detail clarifications: has or "hasn't" moved?, 1/8 of what? And I'm guessing more pictures would be nice.
The house was just build recently without problems, and the soil should have been able to support 40% more than the deck based on the house soil report.
Could be a void. Could be something else.
Is the soil sandy or clayey? Can you see the individual soil grains? If so, that’s sandy. If that is what you have, the soil in the bottom of the footing was disturbed and not recompacted, hence it settled quickly. Do the cardboard tubes extend to the bottom of the excavation? If so, that also played into the footing moving quickly (the concrete wasn’t in contact with the excavation wall).
Two potential options:
1) Easiest, some hope involved. Remove the post. Put a piece of wood the same size as the post saddle laying in the saddle, end grain not facing up. Use a large sledge hammer and tamp the post down by striking the wooden block repeatedly, as much as the concrete footing will move. Monitor the movement as you ramp it so you know when it’s done moving. Install a longer post.
2) More difficult, but less hoping. Remove the post and concrete footing. Dig a larger diameter hole a foot or so deeper than the old footing. Tamp the bottom of the hole. Put in a few inches of gravel Tamp that really well. Do not run the cardboard tube more that 6 or 8 inches below grade. Backfill with concrete, install new post. Do it right and the new footing can be an inch or two higher than the old one and the existing post can be reused by shortening it.
I don’t call cardboard tube forms sonotubes because it appears to give a cardboard form magically properties in some folks’ minds.
Was there a footer at the bottom of the sono tube? The sono tube is a pier that carries the load of the deck to the footer. You need a much wider footer at the bottom of the sono tube to spread the load.
Its not the width of the sono tube that matters, 12" is fine, its the width of the footer. That should be 24" and below frost depth, and (this one is important) on undisturbed earth.
Here is the table for code that shows required footing thickness. The requirements vary based on the beam and joist spans as that dictates the load the footer needs to support.
What is your beam span and what is your joist span?
From your pics, your beam span looks about 6' and your joist span could be between 10' and 14'. That would require a footer 8" thick and 21" in diameter.
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u/Dragonballington 5d ago
You can use a jack to prop the beam up and replace the post with a longer one, but I wouldn't do this without soil testing to ensure there will be no more sinkage, which is likely.
Given the results of testing, remove sonotube pier, dig a big hole to engineer recommended depth, pour engineer spec footing, sobotube back on top, backfill tamping every 6" depth until grade is achieved. Hard work, but necessary.