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

SnagDump

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You've received good advice from DodgeMan, Orezok and Crashz. Here's a rehash from another Civil Engineer. Consider what you are going to spend on the structure vs the cost of fixing your site before gambling on the uncompacted fill.

It may not be all that expensive to strip it off including 6" or so of the supposedly undisturbed areas and have a legit excavation contractor recompact it in lifts. This is starting out as a hay barn but you know how it goes - at some point you may want it to be something more.

Yes you can auger down to undisturbed soil if you can find an auger long enough and big enough to set whatever size blocks you need as bases for the posts. But, the slab is another matter entirely. The cost of a heavily reinforced slab to maybe make up for the uncompacted fill will make stripping and recompacting look like a bargain.
 

bcp

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We have a lot similar to yours... gentle slope from right to left of where I wanted to put our barn. Instead of back filling half of the pad, I dug down into the hill side and end up with the barn 5 feet in the ground on the up hill side so my pad was all virgin soil. It also allowed the barn's height to be out of the wind a little more by being lower profile. We put a retaining wall on the up hill side and then the posts are on the inside of that, in the ground, holes dug in virgin soil. Just a thought.
The OP could get the dozer operator back and cut farther into the hill so the entire barn is on undisturbed soil, The uncompacted fill will be a useful area beside the barn.

Bruce
 
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JWR

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The OP could get the dozer operator back and cut farther into the hill so the entire barn is on undisturbed soil, The uncompacted fill will be a useful area beside the barn.

Bruce
Great point. Unless there is something critical about the exact location -- for pete's sake get the dozer back and do what bcp said. Much cheaper ( and better) than these other schemes. If the footprint must stay where it is, the dozer could also go a long ways toward compacting the soil . These other solutions are way too complex and iffy. The other thing is -- a great question was asked : Is this "just a pole barn ?" I think the answer is YES and thousands of them have been built, many thousands, without worrying over any of these issues. If I were you I'd have the pole barn installer do the posts and emphasize to him what is fill and not fill. Ask hm to do a little bigger hole with a ;little more concrete fill around the posts than he might have planned. They will have mucho experience compared to us peanuit gallery inhabitants. I would also put gravel in for the floor and use it a while and add the concrete next year.

And one more for pete's sake: YES, do a good trench around it, back several feet, and route the water away from the foundation.

Note: and this is guesswork, if you are doing this pole barn yourself (?)you won't be out quite so badly if it has a few flaws. If you are using a good local contractor who installs several pole barns a week you will be a heck of a lot better off letting him deal with the entire issue. In the long run it will be cheaper, esp. if you have other things to do.
 

EddieWalker

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You are getting a lot of good advice that would apply if you where building a house. They are also suggesting that you spend massive amounts of money on a pole barn, which is the cheapest type of structure to build.

Since this is a pole barn, the only thing you really need to worry about is the stability of the poles in the ground. Soft soil will not support the weight of the building and over time, you will have movement in the building. The poles need to be in virgin soil. If you have 8 feet of fill, I would want my poles to be at least 11 feet in the ground. For maximum strength, you want that pole to be continuous from the bottom of the hole, to the top of the wall. This might not be possible, so some engineering will be needed if you go with a 16 foot post and sister on another post on top of it. It's doable, you just have to really think of the best way to do this, which I'm unsure of right now.

The link above shows an auger that will get you down that deep for a very affordable price. When I was a kid, my Dad dug a hole in our backyard 30 feet down for a well to water our yard. He did it next to our 2 story house, and I was on the roof pulling it up with a rope, and then holding onto it while he emptied the bucket, and then later on when it got deeper, he would take the pipe apart and pull up what was in the hole while I held onto it, then he would put it back together and I would help lower it from the roof. Eventually he got an electric winch on a tripod to help pull it up, but that was near the end and we where pulling up gravel and not really getting any deeper. That was pure torture as a kid having to help him do that. It was a family nightmare with my brothers and Mom helping, but with determination, we got it done. Drilling down 12 feet would be easy!!!!!

I would not pour concrete on that soil. It will crack and settle. There are ways to pour a floating slab on soft soil that would work, but it's a huge expense and not very practical for your situation. I would use gravel and expect to add more gravel over time as the soil settles.

I would not bring back the dozer, or hire somebody else to fix the soil. It will still settle with that much fill unless you spend a massive amount of money to do it right. that would mean a water truck and loader to mix the soil before spreading it, then a vibratory sheepsfoot roller to compact it in lifts. The size of the lift is determined by the size of the roller. This would have to be done for the pad, and also the soil that slopes away from the pad.

This is not a house or a shop. Move forward in building it as a pole barn with the knowledge that you have to overcome that much fill material. This isn't hard or complicated. It's not even expensive in the grand scheme of building things.
 

Hay Dude

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I’d dig further back into the bank if possible to keep my footings on virgin soil. get back to a point where the footings are maybe submerged 3’ in fill, not 8’. Thatll make post hole digging a lot more reasonable. Doesn’t look like you’d have to go back real far. Youll be able to make use of the built up area for unloading and parking.
 

FTG-05

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If you decide to make do as-is, a couple of ideas to "accelerate" the settling/compaction::

- Add a good layer of gravel to the surface and then start parking your vehicles on it. Make sure to back and fill every time you park to compact different areas.

- Got a neighbor with a big truck? Offer to let him park on the gravel pad.

- Got a pond or creek nearby or are you on a well? Wet and soak the pad each and every day it doesn't rain.

There's a filled in area near where I used to live in Madison AL. It was probably filled in 50' or so over +20 years. Except for the water idea, the owner allowed people to park on it all the time. I don't know if it was compacted in lifts. There is now a convenience store on the property. It's located at the corner of Shelton and Old Madison Pike or at: 34.706946° -86.723776°

Oh and I just noticed that there's a bunch of houses behind (to the north) of it. Guess it was worth filling in over all those years.
 

Hay Dude

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If you decide to make do as-is, a couple of ideas to "accelerate" the settling/compaction::

- Add a good layer of gravel to the surface and then start parking your vehicles on it. Make sure to back and fill every time you park to compact different areas.

- Got a neighbor with a big truck? Offer to let him park on the gravel pad.

- Got a pond or creek nearby or are you on a well? Wet and soak the pad each and every day it doesn't rain.

There's a filled in area near where I used to live in Madison AL. It was probably filled in 50' or so over +20 years. Except for the water idea, the owner allowed people to park on it all the time. I don't know if it was compacted in lifts. There is now a convenience store on the property. It's located at the corner of Shelton and Old Madison Pike or at: 34.706946° -86.723776°

Oh and I just noticed that there's a bunch of houses behind (to the north) of it. Guess it was worth filling in over all those years.
Puddling is a technique I’ve used, but it has to be done in layers or lifts or it won’t soak through that much soil
 

Golden Rocket

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Instead of staring all over from scratch - I would ask this - why not use screw piles rather than cement piers - around here setting in a screw pile cost 200 bucks (on average) per pile. Is there a strong reason to not use them - they do go in as deep as needed to be - starting length is 7 foot with a 24" foot (the screw) - the pressure built up from the resistance during the install, convets to a weight bearing capability - seems pretty simple, BUT certainly not a DIY unless you happen to be an installer yourself.
 
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MasseyFerg231

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I build commercial buildings for a living and have been in this industry for 25 years. Many moving parts, involved. Several good comments above from Crashz (trash in dirt, proofroll), Dodge Man and some others. Virgin soul doesn’t always mean it’s good and has adequate bearing capacity.

The projects our company builds are in the $5million to $40 million dollar range. The Geotech Engineer does a soil boring to advise the structural engineer on how/what the soil can handle and adjust for any any poor soil conditions. This helps to establish a set of conditions/specifications that can be bid Apples to Apples and can be monitored by a third party to ensure that the owner is getting what they are paying for. If the process fails to meet the specifications, this allows the owner legal recourse (breach of contract) to correct the deficiencies. all of this adds costs that the owner I ultimately pays for. That being said sometimes local (non-degreed) knowledge can be better than all the testing in the world. With the pictures of the concrete trash and fill placed over topsoil, I hope you didn’t pay the guy much for the work.
 
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