Explain concrete sonotubes to me

[bdog]

I have a project coming up where I might use these as I will need ten piers slightly raised above ground level. What I have been reading and seen on you tube people dig a hole and shove the tube all the way in the ground and fill it up. Why?

It seems to me it would be much better to dig the hole and only shove a few inches of the tube in the hole and then fill it up so that the concrete fits and fills the hole completely and will be solid. Shoving the tube all the way in seems like it would just wind up being a wobbly weight as the tube isn稚 going to fit the hole perfectly. Concrete is heavy but it is pretty easy to wobble it around on the end of a pole if it isn稚 firmly seated in the ground.

Here is a video of what I am talking about. How to Build Deck Footings with QUIKRETE® - YouTube

 

[ch47dpilot]

I've always thought the same thing. But its done a lot so it must work.

 

[Erik M]

The smooth surface of the tube is less likely to be grabbed and lifted by surface frost action.

 

[Aquamoose]

A sonotube reduces waste of concrete. Sticking only inches of the tube is counterproductive as it does not provide adequate frost heave protection and waste concrete. The amount sticking up to meet the anchor level provides a clean look, that’s important but it’s important to stick a certain amount below ground for the aforementioned reasons.

 

[Streetcar]

Bdog
When I use sonotubes, they are only partially inserted in the hole.

 

[marchanna]

It all depends on your climate. In Canada we dig down four feet so that we are below the frost line. The method in that video wouldn’t do us any good because it would heave every year up down and sideways.

 

[Rustyiron]

These are popular around here for a good footing & up lift wind loads Bigfoot Systems Footing Forms save time, save money: decks, renos, new construction

 

[GLyford]

bdog, where you are, you are right, there is not much point. As others have said, up here in the frosty rustbelt there are reasons to go deeper with them.

But even then, there have been a few times with non-critical structures when I have poured concrete into a cleanly augered post hole (still 4' deep, mind you) with a chunk rebar hung in the hole, and either a short chunk of sonotube or a square form for the part that shows above ground. But then, being on sand where the water all drains away and just doesn't sit in the soil in clay or silt, I can get away with that and the frost is less likely to cause trouble.

If you are on expansive clay, that might be one reason to use a deeper tube? I wonder if expansive clay down your way lifts poles the same way that frost does up here. If so, a footing that the soil has a harder time sticking to might be an advantage there, too.

 

[crazyal]

I think it's also to prevent the hole from collapsing. It could be days before you pour cement. Also, depending on the size of the tube you may need to put a footing in like a bigfoot (I use a large rock) at the bottom so the hole is going to be much larger than the diameter of the post and require backfilling.

 

[newbury]

I have a project coming up where I might use these as I will need ten piers slightly raised above ground level. What I have been reading and seen on you tube people dig a hole and shove the tube all the way in the ground and fill it up. Why?

It seems to me it would be much better to dig the hole and only shove a few inches of the tube in the hole and then fill it up so that the concrete fits and fills the hole completely and will be solid. Shoving the tube all the way in seems like it would just wind up being a wobbly weight as the tube isn稚 going to fit the hole perfectly. Concrete is heavy but it is pretty easy to wobble it around on the end of a pole if it isn稚 firmly seated in the ground.

Here is a video of what I am talking about. How to Build Deck Footings with QUIKRETE? - YouTube

Looking at that video I wouldn't trust the concrete stability any where above ground level. The ONLY use of rebar was to get the air out. The video does tell you to put the tube sufficiently below the frost line. Apparently others didn't see that.

You should pack the hole after finishing the tube and that will prevent wobble.

 

[oosik]

The log cabin I built in Alaska in 1976 stands on raised sonotubes. Dig a hole to a depth well below the frost line - five feet in my case - fill the hole with cement - jab the sonotube into the wet cement and adjust the height to be on grade. Push a round wire cage inside the sonotube and half way into the wet cement. On a 12" diameter sonotube - use a 6" diameter wire cage about two feet long. One foot pushed into the wet cement - one foot out of the cement and centered inside the sonotube. Fill the sonotube with cement - check that top of sonotube is on established grade and adjust as necessary.

These sonotubes on the cabin have stood tall, strong and proud now for 42+ years.

 

[marchanna]

I used to put them in will footings also, but none of the building codes here require it.

With the metal reinforcement mentioned above and a thick wide footing, you can use a much smaller diameter sonotube, but it is a little more work.

 

[bdog]

We don’t have frost heaving here to worry about and no problems with expansive soils. I have set hundreds of fence posts around my place in concrete and never had one move.

I did however try to relocate a fence post once and it didn’t work. Had a post set maybe 3.5’ in the ground in concrete and pulled it out, concrete and all with the loader. Augered a new hole for the post with a larger auger and placed it in there and packed dirt around it the best I could. It was not stable and if you grabbed the top of the post you could move it around. Seems like these sonotubes would be the same way if they were shoved all the way to the bottom of the hole even if you packed dirt around the exterior of them.

 

[EddieWalker]

I watched the video without the sound on, so I might have missed something. In my opinion and experience, compacted soil around a post is always softer then undisturbed soil. When you have a really heavy rain, that soil will wash out. So putting the sonotube inside the hole and then filing in around it with loose soil and trying to compact it will never give you as much strength as you would get if you just filled the hole up with concrete and let the undisturbed soil contact the concrete.

If frost heave is a big issue, digging out the bottom of the hole bigger and then lowering a sonotube into the hole part way has merit. You create an anchor that way, and a larger footprint at the bottom. It's not a concern for me where I live, so it's not something I'm ever going to do.

The only time I use sonotubes is when I want to extend the footing above grade. Usually for setting a post on. I decide how high above grade my deck or pad will be, and then add an inch. Then when I pour my pad, it's still an inch high so water cannot get to the bottom of the post.

The other thing they did that really confuses me is putting gravel in the bottom of the hole. If you just left the hole empty, it would act as a bowl and hold water long after the rain is gone. The undisturbed soil will absorb some of the water, the rest will run off. What is absorbed will go sideways to where the hole is and keep it filled for longer. Adding rock just creates voids for the water to remain in the bottom of the hole longer, and actually draws in more water then if there wasn't any rock in there.

Keep it simple. Dig your hole as deep as it has to be for your area, fill it up with concrete and only use a sonotube if you need the concrete to go up higher then the surrounding grade.

 

[bdog]

In my opinion and experience, compacted soil around a post is always softer then undisturbed soil. When you have a really heavy rain, that soil will wash out. So putting the sonotube inside the hole and then filing in around it with loose soil and trying to compact it will never give you as much strength as you would get if you just filled the hole up with concrete and let the undisturbed soil contact the concrete.

This is exactly what I was try to say is the problem I see with putting the tube all the way in. If you dig a hole and put a post in it and fill with dirt it will never be stable. However if you drive the post in which many people are doing here now it seems to work fine.

 

[marchanna]

It all depends on your climate and soil type. Frost is the biggest factor. Around here, driven in posts don’t work at all they heave so bad that I have seen wood fences collapse after just a couple years. What I see a lot of fence installers do is auger the hole and pour the concrete and set the post right in the hole. It seems to hold up well for many years and it is quick and efficient.

 

[Cord]

They're setting them all the way down so they don't have to support the tube and it'll use less concrete. Depending on your soil type, the tube can help to restrain the soil and help save the pier if it should slump. Personally, I'd prefer to have the pier be tight to the hole wall because the earth will help stabilize the pier. Unconsolidated backfill will contribute no lateral stability. The frost upheave on the side of a pier is minimal and is typically not considered. It's more important the bottom of the pier be extended below frost and the bottom of the hole be clean of any loose spoil. You should add at least one piece of rebar to provide some tensile strength to the pier.

I will say that Waxahachie Texas was the second worst project that I had for expansive soils. The worst site was southwest of Denver.

 

[MossRoad]

I think those tubes are meant for piers, not fence posts. There's a big difference. Piers support weight and let you use posts not sunk into the ground. Great for wood deck posts and preventing rot due to ground/water contact. I don't think you'd want to use tube forms for fence posts.

 

[npalen]

Read thru the posts fairly fast but didn't notice that anyone mentioned what happens if/when the tube itself deteriorates. Not proclaiming a problem with that but just something that probably happens over time.

 

[MossRoad]

The tube will rot away. They can be removed, if desired, by making a slit on two sides, then around at the depth you want to remove it, then peel it off. It's waxy coated inside for easy removal.