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I recently poured some concrete piers with sonotubes. Not sure why I did this, but some of them I had the tubes about 1 foot into each hole. I started with filling the tubes and then backfilled around the tube with more concrete.

It did not occur to me until after that eventually that cardboard tube will disintegrate and I will be left with a small void between the pier and backfill. I realize now that I made a couple mistakes. First, dont backfill with concrete and second, dont put your sonotube that far into the hole. Its not necessary now that I think about it.

Anyway, these piers are done and repouring is not an option right now. It will be next to impossible to remove the cardboard between the backfilled concrete and sonotube. I thought of maybe soaking it with something and lighting it to burn it out and then fill the thin void with pure cement.

Can anyone think of a way I can remedy this? I dont think it will be an issue for a while, but down the round it could cause some problems. Most of the tubes only went into the hole about 6 inches but some were more like a foot. I am in an area that does not have a frost line and am in hard packed clay for what its worth.

I did use rebar in every pier for those wondering.

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    What is the diameter of the sonotube, what is the reinforcing in the tube, what is the distance from the sonotube to the side of the excavation wall?
    – Lee Sam
    Jan 19 at 0:56
  • The tubes I used were 8", rebar in the tube with a j-bolt in the center and the distance from the tube and wall varied a bit. Some from 1" to 6"
    – Ronnie
    Jan 19 at 4:47
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    What is going to rest on these 8” tubes? How far apart are the tubes?
    – Lee Sam
    Jan 19 at 4:53
  • I am building an off grid cabin (20x24, 9 piers), they are approximately 7 ft apart
    – Ronnie
    Jan 19 at 4:55

2 Answers 2

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There are a few issues:

  1. Seismic: You live in an area that is seismically active. That means your pier you just poured needs to be braced down in the ground to keep it from tipping side to side. Piers are considered “pin” connections. That is to say, they must be deep enough and designed to not tip.

  2. Reinforcing: Of course the pier needs reinforcement designed to resist structural loads to support the house (you didn’t mention what the piers will support), but it must also needs adequate reinforcing for adequate relation between rebar and concrete. Without that reinforcing the concrete pier could crack and fall apart.

  3. Fire… Burn the Sonotube: Your suggestion to burn the sonotube up creates a void which allows the pier to rock sideways and can harm the rebar close to the edges.

  4. Excavation around the Sonotube: Now that you’ve filled the area between the sonotube and edge of the excavations with concrete, that “backfill” is not uniform in thickness and will crack at the thin spots (sides). This will eliminate any backfill holding resistance you may have planned on.

These are all Building Code violations. Obviously you didn’t get a permit. I’d suggest you talk to an architect or structural engineer (not a civil engineer) and then get the permit.

Note…Edit: I’d remove the piers and start over. 1) The piers do not extend far enough into the ground for lateral resistance. 2) The Piers are not reinforced adequately to resist lateral loads, 3) The piers are not designed for x-bracing and do not have notches, braces, etc. to add x-bracing, 4) If a building is installed on the piers, the piers will sway due to wind load , 5) The piers and building are located in a seismically active area and is not designed for such stress.

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  • 1. I am indeed in a seismic area and my piers are all about 3ft deep with no more than 6" of tube above grade. 2. If you were looking down the tube I formed a triangle with 3 vertical rebars for the reinforcement. 3. I did suggest that, but I also suggested filling that void with a very wet pure cement to hopefully fill it. Also no rebar would be exposed. 4. good to know.
    – Ronnie
    Jan 19 at 4:53
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If the backfill was placed around the sonotube, you have no hope to get the rotten material out without getting rid of the backfilled concrete (which I don't understand why you have chosen for backfill in the first place). If you have only poured it in the past few days, the concrete shouldn't be too tough to drill/chip out as it hasn't fully cured and hardened. But you have to apply the forces carefully when getting closer to the tube, so the pier wouldn't be damaged. Good luck.

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  • I backfilled it with cement because I am an idiot and was not thinking clearly.
    – Ronnie
    Jan 18 at 23:47
  • I hope you were using "Concrete - sands, and stones mixed with cement" for the pier, not the pure cement which is very brittle after hardened.
    – r13
    Jan 18 at 23:53
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    It's not the time to blame yourself. If you decided to demo the backfill, you should soak it with plenty of water the night before, and continue to add water while drilling/chipping. The water will dampen the vibration, which is harmful to the semi-cured pier.
    – r13
    Jan 19 at 0:02
  • It was indeed concrete, not just cement. Lots of stone and sand mixed in. It was a total of 1 yard with 6 bags of portland cement, but it was poured about a week and a half ago so I may be SOL on this one.
    – Ronnie
    Jan 19 at 0:13

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