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candie_lea
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# Posted: 19 Jul 2023 18:24 - Edited by: candie_lea
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Hello everyone,
I have a question about pier foundations. What can be beneath the footings when undisturbed soil isn't an option? Here is the situation:
We recently finished hand digging the footing holes for our pier foundation. Here in the Ozarks, we only have to go about 18 inches deep. My whole family is building a cabin bunkhouse for our homestead, and we are doing all the work ourselves on as much of a budget as we can manage. The cabin is 16' x 56'.
Things were going well until the last 5 footing holes on the east end of the cabin. We ran into a log beam in the bottom of one of them. In a couple others, we hit ash, pieces of wood, and barbed wire. When we had our storm shelter put in, the guys said sometimes people burry their slash piles out here. When we had our septic system installed last week, the man doing the work hit all kinds of debris -- several large logs, lots of cattle panels, and farm equipment. We know this portion of our land was logged several years ago, and was used for running cattle in the recent past. It appears all the waste was buried under our build site.
I had started to worry about our piers being over this mess. Thankfully, the guy doing our septic confirmed our concerns and told us we needed to dig down past the burn pile to the hardpan soil.
So, we have been been digging for a few days. In one hole, my brother took us about 3 more feet down to reach the hardpan. (It makes no sense -- was this burn pile in hole?) In Missouri, they don't recommend cmu piers be longer than 4 feet. We need the pier on top of something. What can we fill the holes with that won't settle and will bear the weight of the footing, pier, and house? Should we fill the holes with concrete? Gravel? Rock?
We considered moving our build site, but with the septic, electric, and water already in place, we don't know how we could do that.
If you made it through this long post, THANKS for reading and any advice you have!
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spencerin
Member
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# Posted: 20 Jul 2023 00:01
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How many feet above ground will your cmu piers extend?
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DaveBell
Moderator
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# Posted: 20 Jul 2023 02:21
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I would talk to the county building engineer folks. If you get their concurrence on what to do, it might save you a problem with insurance if the house sinks. One thing I might do is switch to a slab foundation.
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jsahara24
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# Posted: 20 Jul 2023 09:14
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Definitely need to dig below any debris/construction material.
Then I would look into using a spread footer (i used bigfoot) and set sonotubes on top of that....that will keep your concrete to a minimum, and allow you to come up out of the ground as necessary while maintaining a good footer.....
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Brettny
Member
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# Posted: 20 Jul 2023 10:38
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It looks like that soil is prety darn hard to begin with. If your worried you can use big foot footings on the bottom of the ones your really worried about.
Or you could just pour a standard sono tube, build like nothing every was found and come back in a few years to re level if needed.
No matter what you do I wouldnt put the building so low that you dont have acess to relevel later if needed.
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candie_lea
Member
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# Posted: 20 Jul 2023 18:59 - Edited by: candie_lea
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Quoting: spencerin How many feet above ground will your cmu piers extend?
We are building on a slight hill, so each pier is different. The tallest pier will be about 3 feet out of the ground. The problem holes are under the taller piers.
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candie_lea
Member
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# Posted: 20 Jul 2023 19:03 - Edited by: candie_lea
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Quoting: jsahara24 Definitely need to dig below any debris/construction material. Then I would look into using a spread footer (i used bigfoot) and set sonotubes on top of that....that will keep your concrete to a minimum, and allow you to come up out of the ground as necessary while maintaining a good footer.....
We are building piers with 12" x 16" x 8" blocks. We already have purchased the blocks, or else we could have considered Sonotubes.
Our county has no building codes, but our neighboring county recommends that concrete block piers do not extend higher than 4 feet above the footing. I wondered, though, if we could go higher with our piers since we are filling them with concrete and rebar? (The neighboring county code assumes unfilled blocks.)
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ICC
Member
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# Posted: 20 Jul 2023 21:01 - Edited by: ICC
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Quoting: candie_lea ...higher than 4 feet above the footing
Above the footing or above the surface grade? Huge difference.
You are getting advise to go down to hardpan, or undisturbed soil. That is good advise. There is no knowing what trash is down there. That is a big concern to me. Anything organic that could be buried will eventually rot away.
The height of a concrete column or a filled concrete block column is partially limited by the lateral support as well as the footing. Under code a pier foundation is not acceptable unless engineered. Just an FYI.
Bigfoot footing bases are about the best available for use with sonotube columns. Even they did not have the required certification for use in s residential habitable building without an engineering report. Could you return the CMU's and switch to Bigfoot. You would pretty much need a backhoe or excavator for the holes though.
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spencerin
Member
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# Posted: 20 Jul 2023 22:09
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Just a question -
Are you sure the TOTAL length of the cmu piers shouldn't be longer than 4'? I'm guessing that's the longest they should be above grade only. I would double-check that. If it applies to above-grade length only, then don't fill the holes partially back up, just start your piers at that depth as it otherwise won't matter, especially if filled with rebar and concrete.
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candie_lea
Member
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# Posted: 21 Jul 2023 11:02
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Quoting: ICC Above the footing or above the surface grade? Huge difference.
Quoting: spencerin Just a question - Are you sure the TOTAL length of the cmu piers shouldn't be longer than 4'?
Above the footing, per our neighboring county code. But that assumes unfilled blocks. Since we are filling ours with concrete and rebar, I wondered if we could just build them the additional 3' longer underground? We can have our footings (24x24x10 concrete with rebar) on the hardpan at the bottom.
We cannot return our blocks. We are a long way out of town and had to have them delivered. We have no codes -- no building department -- out here. No requirements of an engineer. We chose a simple foundation that we felt confident we could complete.
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pabear89
Member
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# Posted: 21 Jul 2023 11:35
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What about building a rebar cage to insert into you holes and fill with concrete? this would allow you to startup your blocks at a preset level, considering the various hole depths to clear the debris field below.
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Brettny
Member
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# Posted: 21 Jul 2023 11:39
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Since your useing concrete blocks I would pour a wider 6in thick footing and leave rebar sticking out. Then put your blocks on that and fill them. Should be plenty strong and need just a few more bags of concrete.
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spencerin
Member
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# Posted: 21 Jul 2023 11:50
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If there is truly no code enforcement where you are, then what Brettny suggested is good. Don't fill it back in, just start there with the concrete footing.....
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candie_lea
Member
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# Posted: 21 Jul 2023 12:09
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Quoting: spencerin If there is truly no code enforcement where you are, then what Brettny suggested is good. Don't fill it back in, just start there with the concrete footing.....
Maybe we will try that. We can pour a thicker footer, and it will only be maybe 3-4 extra courses of block.
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jsahara24
Member
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# Posted: 24 Jul 2023 09:58
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Quoting: Brettny Since your useing concrete blocks I would pour a wider 6in thick footing and leave rebar sticking out. Then put your blocks on that and fill them. Should be plenty strong and need just a few more bags of concrete.
Based on the fact that you already bought the block I think this is the best advice.....and definitely pour your blocks solid..
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