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Old 11-13-2009, 06:15 PM   #1
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Sinking footing tubes


Hi All

I am new to the DIY chat room.

I am building a barn with a local builder using The Footing Tube (8" at top and 5.19 feet deep) footings. The 40 x 40' two story barn is built with these footings every 13.5' along the perimeter and 6x6' pine posts. We decided to add the second story a bit later on a whim and added regular 4 10" sonotubes (4' deep) in the interior to support the second floor (knowing it would be dry in there we figured it would be enough).
The second floor is actually 60' x 40' and cantilevers out over a washstation area for processing vegetables.

We poured the concrete piers around september 15th and now they are sinking. Over the last month they have been sinking differentially. At first we noticed one under the cantilever sinking (it has now sunk over 3" and we continually jack up the post and add wedges under the beam). I wasn't too surprised about this because the ground around the barn and in the washstation (under the cantilever) hasn't been graded and had sunken around the piers since we have been getting allot of rain over the summer and fall. Furthermore this was one of the 10" sonotubes we added later and it wasn't set as deep and without the footing that 8" The Footing Tube has incorporated into its structure. However, now there are several of the original footing tubes that are sinking a 1/4 in here and 1 1/2 there. This is beginning to cause concern. My builder assured me at the time that we could support a second floor since we used such large footing tubes to begin with. Is the load a problem?

My conclusion is that the tubes had been set in a trench (5' deep and 3' wide) dug around the 40 x 60' perimeter with a hi hoe and this trench settled as a low area in the landscape gathering water over the month or so while we built and added extra weight.

So, what can we do? Keep jacking up the posts and eventually replace them with precut post? Will the ever stop settling?

There is no gravel under the footing tubes. The barn has an earthen floor. I am starting to landscape so water flows away from the barn and lay a tile drain under the eaves to collect any roof water.

Any suggestions or comments would be appreciated as I am caught at unawares, not being a professional builder myself, and the project is still going forward adding more weight as we put the metal roof on.

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Old 11-13-2009, 06:36 PM   #2
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Sinking footing tubes


Farmer, Welcome to the Forum
You have some serious issues that should be looked at by an engineer and a geologist. To get more help on this Forum I suggest you post some Pics and include your location.
From what you say so far I wouldn't have much confidence in your "local builder".

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Old 11-13-2009, 06:55 PM   #3
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Sinking footing tubes


I agree with Bob. Your piers, without square footings under them are way undersized. Look at this for decks, way lighter than a building: http://www.awc.org/Publications/DCA/DCA6/DCA6-09.pdf
Be safe, Gary
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Old 11-13-2009, 06:57 PM   #4
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Sinking footing tubes


I am trying to upload photos. But even at lowest quality they require too many KB. I hate to say the builder doesn't do good work. The rest of the barn is well built and he seems quite competent. He has build the entire building with one extra helper and is just finishing up custom roof trusses. However, there is a question of the piers. I am at the tail end of my budget. It seems like I need to get water to flow away from them. A geologist could probably give me some more detail about the clay/sand and pit run type soil I am on. With winter coming I am worried to get this solved. Is a geologist going to run me a large bill? What info might he/she provide?

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Old 11-13-2009, 07:10 PM   #5
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Sinking footing tubes


here is a photo..
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Old 11-13-2009, 07:12 PM   #6
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another photo of barn
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Old 11-13-2009, 07:37 PM   #7
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Sinking footing tubes


If it is sinking, it is probably due to the soil and small size of the footings.

An 8" or 10" Sonotube is really not large, but minimal, if the bearing soil is marginal. Frequently, home decks are built using 10-12" or 16" Sonotubes and sometimes with a a "bigfoot" to spread out the load over a larger area.

If the soil is poor, one foundation tube will settle until it goes far enough to transfer to the other footings, so they have more load and will settle more until they can transfer the load to other places. This is common with flexible buildings that flex and move to transfer the loads. More permanent structures with conventional footing do not flex until they crack due to the settlement, so they "float better".

Supporting a 2400 sf area on 4 Sonotubes is really not realistic.

A professional may be able to give you some advice now on what to do, but it is a little late for professional help since what was done is done. Correcting errors is also much more expensive than doing it right for your site.

Make sure your concrete slabs are separated from the building structure (posts and "footings"), so that is not influenced by the poor soil that is apparently under the barn. Fortunately, a barn is flexible and settlement will be slow. Since you are processing the vegetables and the equipment is not heavy and the loads the concrete slab it is on should be adequate since a concrete slab that is thick enough will do the job of spreading the loads.

Building "on a whim" usually is not the best thing to do.

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Old 11-13-2009, 07:58 PM   #8
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Sinking footing tubes


you may need to look at underpining your sonotubes with a sread pier/footing. someone will need to give you size and strength. have underpined in the past on projects the y are labor intesive. bfoere more weight is probably better than after. good luck
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Old 11-14-2009, 03:49 PM   #9
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Sinking footing tubes


Hi all

All comments have been helpful.

In response to Concretemasonry: "Supporting a 2400 sf area on 4 Sonotubes is really not realistic."

The barn is built on 20 8" x 5.2' footings around perimeter of barn and washstation, 6 10" x4' interior sonotubes, and 2 diagonal braces at entrance to wash area. The greatest distance between any footings is 13.5'.

I have included an excel-generated layout for reference.

Is this layout insufficient for a board and baton barn with steal roof and 1" pine flooring? The Builder thought it was. The building inspector came by and said it was enough also, but agreed that the only reason we could add the extra floor retroactively was because we had put such large footing tubes in originally. So we added interior sonotubes to support the second floor.

I guess I can answer my question: It looks like it isn't sufficient and we needed to spread out the weight more?

Is 13.5' too long a stretch between footings?

Should my builder have been able to predict this settling or is this a freak circumstance due to too heavy a load with my soil conditions and the prevalent rainy weather we have had for months?

I guess my biggest question: will the building have already experienced most of its settling over this fall and spring? My father-in-law thinks so. It definitely seems to have slowed tremendously and we have had unusual quantities of rain this year.

Can we keep jacking up any corners that might sink and wedge them and then replace the posts with new posts custom cut to the new heights?

Or are these footings insufficient to keep this structure stable for years to come?

tpolk mentioned underpinning the footings. How is this done?

I would like to find the most practical solution. Would this be to add more supports to spread out the load? More sonotubes?

thanks again for any input.

Not sure which professionals to go to for advice.
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Old 11-14-2009, 05:33 PM   #10
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Sinking footing tubes


You need to establish that the tubes are in fact sinking, not heaving, based on a careful, accurate instrument survey of the elevations of the top of the piers. You may have already done this, in which case you simplymeasure the elevation of the top of the piers every week or so, to establish the rate at which the piers are sinking. Assuming the piers are sinking as you state, the cause is probably inadequate bearing capacity of the underlying soil. Spreading the load out to more piers may not solve the problem, it may simply slow down the rate of sinking, which would merely postpone inevitable structural failure of the building.

You need a geotechnical engineer to examine the soil, using a backhoe or a drill rig, to determine the allowable bearing capacity of the soil, and how deep the tubes need to be placed. Any discussion about the capacity of the tubes without detailed soils information is premature, and not likely to lead you to a solution. I understand you are short of money, aren't we all, but it is going to cost you a few thousand dollars to get some borings and an interpretation of the data. Shimming each pier as it settles may be a viable solution, but I would not count on it, and that looks like a pretty expensive barn to be supported on a sinking foundation.
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Old 11-15-2009, 09:42 AM   #11
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Sinking footing tubes


I should have mentioned soil testing in my previous post on underpinning to establish size of spread footing. sorry for omission. timothy
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Old 11-15-2009, 12:17 PM   #12
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Sinking footing tubes


Perhaps a review of the situation with a foundation repair specialist. I lived in New Orleans where sinking houses were not incommon due to soil conditions. The foundation repair companues knew the area soils, had appropriate engineers available, etc.
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Old 11-15-2009, 04:22 PM   #13
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Sinking footing tubes


Quote:
Originally Posted by Farmer Z View Post


In response to Concretemasonry: "Supporting a 2400 sf area on 4 Sonotubes is really not realistic."

The barn is built on 20 8" x 5.2' footings around perimeter of barn and washstation, 6 10" x4' interior sonotubes, and 2 diagonal braces at entrance to wash area. The greatest distance between any footings is 13.5'.
8" sono tubes aren't large by any means, regardless of what your builder & inspector think. In fact, they are the smallest dia. tube available as far as I know. They are just basrely large enough to rest a 6x6 on, and that's IF each posthole is perfectly aligned.

I'll admit I'm no engineer, but did some quick math using the minimum allowable bearing capacity of common soils in MY local code requirements. That value would allow for a maximum of about 20,000#'s loaded on the tubes you listed. This includes the building + the concrete in the piers.

Using the bearing value for very hard, dry clay would give you a maximum of about 40,000#'s.

I think your building weighs many times more than that, thus the sinking your building is experiencing.

BTW, the fact that your sono tubes are deeper than needed for frost may actually NOT be an advantage to your situation. The extra depth leads to additional weight on the soil.

On another side note, there is a chance that the holes weren't cleaned out sufficiently after being drilled & the concrete was poured on top of some loose dirt. That will definatly make the tubes sink rather fast. Regardless, I'm positive the sonotubes you currently have are NOT adequate for the building above UNLESS they're sitting directly on bedrock.

I also agree with Dick that this isn't going to be a easy or cheap fix. In hind sight, it probably only would have cost a few hundred dollars extra to use 14 or 16" tubes in the first place.
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Old 11-15-2009, 05:53 PM   #14
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The first floor has an area of 1600 square feet. At 20 lbs per square foot (this may be low), the weight of your first floor is about 32,000 lbs. The second floor has an area of 2400 square feet. Again using 20 psf, the weight of the second story is about 48,000 lbs. Total load is about 80,000 lbs. Of course your engineer will check these values, and your code official will also assist you in determining the correct loading for the specific building type, these figures are ROUGH APPROXIMATIONS.

The area of an 8 inch sonotube is about 1/3 square foot. The total area of 20 of these tubes is about 7 square feet. The total area of 6 10 inch sonotubes is about 3.3 sf. Therefore, your barn is supported on a total area of about 10.5 square feet, meaning you would need a bearing capacity of approximately 7000 psf for the soil. I don't know where you live, and I don't know what type of soil you are built on, however for 7000 psf presumptive bearing capacity you would need to be on dense sand or gravel according to the MA building code.

Of course, the actual load on your building may be considerably higher than 80,000 lbs, based on exactly what you plan to put in the building, and the snow load on the roof. You absolutely need to cough up the money to hire a competent engineer to review the building design, evaluate the soils, and formulate a plan for repair of the foundation.
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Old 11-15-2009, 06:15 PM   #15
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Would connecting the piers with a concrete sill around the perimeter or a slab help it float better? If i understand correctly i need to lower the psf that is bearing down at any one pier. So should i not try and retroactively add piers or supports of some sort?

The soil is a glacial till: silt and clay with sand, gravel and cobble.

The other question is, would this building be settling without the presence of water getting under the piers? We had a month of rain after the piers were set and the lowest point was around the piers. So circumstances and poor planning were not working for the building staying level. But once there is quick landscape drainage and subsurficial drainage using a french drain system and the roofing eaves, would the building stop settling?

The reason I ask this is because one pier quickly settled 3 1/2" over two weeks during the rain and the others settled a bit here and there over the course of a month. But now there has been little movement.

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