Quesitons about compaction?

I am working on building up a building site for a barn. I am packing with a sheepsfoot roller and I have a couple of spots where the dirt is starting to pump and was wondering if I should worry about it or if it would be ok? The fill is anywhere from 3 ft to 5 ft of fill and was wondering what harm it could result in the future.

You better worry about it. Undercut it and back fill it with some good material like 3.0" crushed limestone breaker run. If the bad area is under a footing the whole thing could settle and crack everything. If under the slab could settle and crack the slab

I would first ask you to define pumping. With the clay I work with after it has passed a compaction test and a loaded dump truck goes over it you watch the soil rise after the tire rolls over it. It used to worry me but now after the years I have found that is not a reliable indicator. Is your soil real wet? If it is wet and the dump truck is leaving ridges of soil in between the tires and you bring moisture to the top when you drive over it that would make me stop and redo things. Is it a pole barn with a gravel floor? If so you have a little more fudge factor.

mattm said:

I am working on building up a building site for a barn. I am packing with a sheepsfoot roller and I have a couple of spots where the dirt is starting to pump and was wondering if I should worry about it or if it would be ok? The fill is anywhere from 3 ft to 5 ft of fill and was wondering what harm it could result in the future.

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Lots of variables here. Your boil is being caused by trapped water[usually in cohesive soils-clay],or as I like to say-hydraulics at work.NOT good for building directly over such areas for sure. Many times,if it's not too bad,stay off your fill pad for a few days,combined with some dry weather,and it will harden up by itself.You could also excavate the real bad areas also and place some good large aggregate like Greg mentioned and compact that.I take it that you are installing your fill in lifts of something reasonable,like no more than 12'' per at a time correct?

Well when we run the loaded scrapers across it, it will sink down about 1 to 2 inches but will come right back up. We have disced it and let it dry but it still wants to do it. It is a freestall barn cows and the footing should get below where we have hauled in the dirt. The only thing is there will be concrete alleys for the cows to walk on. I was wondering since it is just cows walking on the concrete if it would matter as much. The concrete will also be 6 inches thick and down the center there will be 8 inches thick concrete for the feed tractor to drive on.

Thanks for your responses.

Jim I have posted what is going on and was wondering if you had any suggestions.

Is there a geo-tech on-site?

What you describe sounds like flexing. A heavy clay soil that is on the higher end of the moisture content will pass compaction testing but will still flex under a proof roll.

No for these type of jobs around here nobody usually hires a geo tech. The dirt was a little wetter than we would have liked when we put it in, but it didn't seem like it was anything to worry about. Like i said it comes back up when you drive on it with a scraper, but we havn't driven any concrete trucks across it yet. The other day before we were done they drove a semi across it with 29 ton of rock and they sank in about 3 inches when driving.

I had a job 25 years ago,,, maybe more????,,, building an earthen dam,, soil engineer on site. The vibratory roller made its pass's , the tech stuck his nuclear probe in and said " she pass's" . I said wow look at it bend. He said that might be, but its as compacted as its ever gonna get... So we continued on with the fill /pack pass'. Like I said that was 25+ years ago and its still standing holding a river back.

Looks like you might have too high a moisture content. You may need to either disc the material and let it dry or apply lime to pull the water out and tighten the soil up.

I ran into this issue on a hotel project I did in '08. It was a silty clay soil that we couldn't do anything with. We bladed it with the dozer and let it dry in the sun for a day. Re-bladed and compacted and still pumped when a loaded truck ran across it. What we ended up doing was getting a spreader truck from the local Co-OP to come out and spread agg lime over the lift. Did this on the last two lifts, blending the lime into the material and re-compacting it. The lime did the trick. It tightened up the silty clay and we passed our proof roll.

It wasn't that expensive at the time considering the project but I don't remember how much exactly.

Grandpa posted while I was putting the potatoes in the oven.:tong I have also had techs say the same thing. It depends on the project and the specifications. Some projects require a proof roll and others rely on the nuke test. Personally I prefer the proof roll. If the soil is moving under a loaded dump truck, it's just not suitable for building upon, although it does depend on what kind of structure you are building. The weight of the building and it's applied loads is the deciding factor. This is the realm of geotechnical, structural and civil engineers - it's what they are paid to do. I don't practice jobsite engineering anymore since I have never gotten paid for it - just assumed the liability...:cool2

And burnt your potatoe's..... ha ha hha

dig it out, dig down till you find decent material, fill in with decent material compacting in layers of 500mil at a time.

Matt, I reread your original post and you said certain spots were pumping and bringing the "mud" up. How big are those spots and where are they located? If the spots aren't that big and are not under the footings I might would put extra rebar in the concrete and have control joints every 8 feet or so. At every control joint have rebar every 2 feet and cut every other rebar. This would allow for the concrete slabs to float a little and still have all the concrete stay together and not heave leaving a trip edge. The above applies if the pumping spots are 5' in diameter or smaller. If the spots are under the footings you need to get that right. Are you doing this for yourself or for a paying customer? If you dong for yourself you can take some chances because you will have to deal it. If for a paying customer I would be a lot more cautious and involve them in the decision. I know how some customers don't want to pay to do it right but will be quick to blame you if it doesn't turn out right. I am not encouraging being casual about compaction and I am by no means an expert but your not building a skyscraper I am trying to offer a budget minded pratical potential solution. I can here the engineers and experts shouting at me from here.

We usually dig out the bad spots as soon as the show up because they will follow the fill on up and that just makes more dirt to move to correct it. Normally you need to dig down to the bottom of the probelm to get rid of it, sometimes over x the original ground if it is pumping before starting the fill. I have seen pumping fills pass compaction tests but for peace of mind we usually fix them.

Depending on what "Dirt" Matt is talking about . Any topsoil of course has to come out but I have had good clay sites go very spungey and will move at least a couple of inches when driven over even with a bobcat , never mind about a loaded scraper . We have found that these sites easily pass a compaction test once they have dryed out . Just got to be patient

You say a sheepsfoot, but is it a vibratory sheepsfoot that is shaking water to the surface of your fill?

The soil is a clay, and theres only a couple small spots where its happening at. Theres only one spot where the foundation will go, but the foundation will go deeper than the fill at that part so it should be sitting on solid dirt. I was wondering also if you stick a metal prope down in the soil how much resistance should you feel. Also since we started the project we had over 12 inches of rain and the weather has changed from 90 degree weather to 50 degree weather so there isn't much chance for drying out.

How deep is your probe going in - say pushing it with one hand, just using your arm not throwing you whole body onto it?

12" of rain, change in temps and clay soil. You probably have some pockets of fat clays in the fill causing the pumping in those spots. If it's cost effective, do like the others mentioned and dig those areas out and fill with better material.

The problem will be during construction of the barn if there is just one, I mean just one Lull on the job :cool2, that sucker will find that soft spot and wallow around in it like a hog. That night you will get 6" of rain and your small "soft" spot has become a mucky mud hole that will require a lot more to fix later on, not to mention that Lull will be right back wallowing in the same spot the next morning. Evil bastards those Lulls are....

The dirt is mostly a clay, but we ran into like a gray clay for part of it when we were digging the pond to build the site. There is only a couple small spots maybe 5 to ten feet in diameter. There is only one spot where it is happening where the footing is going, but the footing will be below the fill layer and onto original dirt. As far as the main footing goes I am not worried about that. Since we started the job we have had over 12 inches of rain, and the temperature went from 90 to 50 degrees so the ground isn't really drying out. Anymore and the people we are doing it for don't want to spend the money on lime or anything like that. Just wanted to let you know the conditions. I really appreciate all the responses and help.

mattm said:

The dirt is mostly a clay, but we ran into like a gray clay for part of it when we were digging the pond to build the site. There is only a couple small spots maybe 5 to ten feet in diameter. There is only one spot where it is happening where the footing is going, but the footing will be below the fill layer and onto original dirt. As far as the main footing goes I am not worried about that. Since we started the job we have had over 12 inches of rain, and the temperature went from 90 to 50 degrees so the ground isn't really drying out. Anymore and the people we are doing it for don't want to spend the money on lime or anything like that. Just wanted to let you know the conditions. I really appreciate all the responses and help.

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So--if I understand this correctly your footings will rest on virgin ground[as they should],but your concrete floor will be over a compressable soil.Why not just excavate out these boils and install a large aggregate like 1.5-2.5'' crushed stone in lifts being compacted as you go?Place a geotextile cloth over your sub grade,install a foot of Item #4,compact,pour your floor.