How long should I let new ground settle before putting in posts on piers?

   #1  

rlneal

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A couple of weeks ago, I had a bulldozer come and prepare a site for a new hay barn. Really just a 30x60 shelter for round bales. Mostly. Probably closed in on 3 sides. But there was a lot of dirt being moved around as you can see in the pictures. One end was dug into a bank with that dirt moved to the other end to bring it up so it would be level. There is about 7 or 8 feet a new dirt added on top of the original surface at the one end. The contractor wants to put in concrete piers to set the 6x6 posts onto. We may put down a 15x30 concrete slab on end and it was suggested that we wait a year for the ground to settle before we do that. So then my thought is, do we need to wait awhile before we put in the concrete piers for the posts? I have a 3 pt post hole auger but that is only good for about 3 feet. I do not know how I would auger a 10 foot hole so I could get down to undisturbed earth.
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   #2  

deezler

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Oh geez. 7 to 8 feet of new dirt, that wasn't fully compacted every 6" ? It's gonna settle a lot, and take a while to do it. That said, if you can get concrete down 5 feet, you're probably gonna stay pretty stable.

I've seen skid-steer mounted augers that can go 5+ feet deep. The telephone/electric pole guys go really deep also. The deeper the better in your case.
 
   #3  

dodge man

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I am a land surveyor but my degree is in civil engineering. Like already said if the fill wasn’t compacted it’s a no go situation. The rule was to put foundations on undisturbed earth. If not that then put on compacted fill. I spent some time off and on over the years doing soil testing and density testing. It would take years for it to settle. Putting a floating slab on that is likely asking for trouble.

The good news if just sitting posts on top of piers you will be fine, you just have to go deeper where the fill is deeper. In theory you could tie a floor slab into a series of piers and be good but probably that’s beyond what you want to do. If you put in just a partial slab just put it on the end where you cut and didn’t fill.
 
   #4  

fried1765

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I am a land surveyor but my degree is in civil engineering. Like already said if the fill wasn’t compacted it’s a no go situation. The rule was to put foundations on undisturbed earth. If not that then put on compacted fill. I spent some time off and on over the years doing soil testing and density testing. It would take years for it to settle. Putting a floating slab on that is likely asking for trouble.

The good news if just sitting posts on top of piers you will be fine, you just have to go deeper where the fill is deeper. In theory you could tie a floor slab into a series of piers and be good but probably that’s beyond what you want to do. If you put in just a partial slab just put it on the end where you cut and didn’t fill.
Go deep,.... to virgin ground, for your piers.
Since the dirt floor area will be under your new roof, the filled area will definitely not settle enough in a year without weather moisture.
You will need to wait to pour a floor in the filled area for many years, unless you thoroughly soak that area each week in the warm seasons, for some number of years.
 
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   #6  

orezok

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Uncompacted soil will NEVER reach 90% compaction which is what your engineer wants for structural support. If it did then soil which was undisturbed for millions of years would be 90% or greater.
 
   #7  

4570Man

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They should’ve used a roller and compacted it as they went.
 
   #8  

crashz

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I've tested "virgin" soil before and found in to be in the mid 70% for compaction. But that's why proof rolling before constructing a foundation is a good idea.

You have a couple of challenges here:
1. That's a lot to settle. And it won't settle much without a surcharge load on top.
2. It looks like a bunch of concrete and junk was thrown in. This makes it even more difficult because the debris will cause the soil to vary in density as well as cause bridging and host of other issues. Not to mention, they will be in the way of digging for the piers.
3. Looks like the dozer guy just mixed the topsoil and subsoil together. Another win. In doing this, did he push the soil on top of the existing topsoil and vegetation?

Call a reputable excavation contractor. Have him strip that thing down and start new. Pull the organics (as much as possible) and debris out. Rebuild properly, compact in lifts and have him excavate and install the piers. It sucks but I think that's the way to do it right. For the record, I am a licensed civil engineer.

However if you wanted to cheat and gamble, I would rent the biggest single drum vibratory roller that you can get and beat the snot out of the subgrade. Make sure you hit every area at least three times. Level the pad (with a dozer or tractor and serious box blade) and repeat. Level the pad and repeat. I won't guarantee anything, but results would be better than waiting about 50 years.
 
   #9  

4570Man

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I've tested "virgin" soil before and found in to be in the mid 70% for compaction. But that's why proof rolling before constructing a foundation is a good idea.

You have a couple of challenges here:
1. That's a lot to settle. And it won't settle much without a surcharge load on top.
2. It looks like a bunch of concrete and junk was thrown in. This makes it even more difficult because the debris will cause the soil to vary in density as well as cause bridging and host of other issues. Not to mention, they will be in the way of digging for the piers.
3. Looks like the dozer guy just mixed the topsoil and subsoil together. Another win. In doing this, did he push the soil on top of the existing topsoil and vegetation?

Call a reputable excavation contractor. Have him strip that thing down and start new. Pull the organics (as much as possible) and debris out. Rebuild properly, compact in lifts and have him excavate and install the piers. It sucks but I think that's the way to do it right. For the record, I am a licensed civil engineer.

However if you wanted to cheat and gamble, I would rent the biggest single drum vibratory roller that you can get and beat the snot out of the subgrade. Make sure you hit every area at least three times. Level the pad (with a dozer or tractor and serious box blade) and repeat. Level the pad and repeat. I won't guarantee anything, but results would be better than waiting about 50 years.

I agree. Strip it and start over and compact it properly this time.
 

dodge man

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A couple of terms here. % compaction is a theoretical number based on a test called a proctor. It actually doesn’t really relate to the strength of the soil but has more to do with the soil not settling. There are other tests to check the actual strength, the easiest being a hand penetrometer.

If you roll it now, it will only compact the top foot or so, it won’t do much deeper down.
 
 
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