I've built a few pads for shops and garages for other people and never had a problem. Now when I want to make a pad for my own pole shed, I run into problems. I got the topsoil all dug out and the ground was hard as rock but got it ready for fill. I dug what I thought was really good clay to build it up but I don't know if was just too wet or a different clay than other clay on the property but when it dried it cracked all over. This isn't good so I have to dig it back out. I did read that adding about 60% sand will make a big difference so my little job just a lot bigger. I'll have to go to my neighbors back field and haul several loads of sand now to mix in. It must be Murphy's law or something when you your own projects seemed to be jinxed. Maybe if the clay was drier it wouldn't have acted the same way?
Probably too good a clay. If your clay layer isn't too thick, you could probably spread sand over the top, wet it all down and mix it in with a tractor and a good husky rotovator/tiller. Just a thought.
When it was wet it was almost like modeling clay. I can dig it out with the backhoe but what a lot of extra work. Maybe if I would have let it dry out some but I guess it's good to know now rather than after the building is up and I have problems. The neighbors back field has about a 5' layer of sand and you can drive on it and not make a dent so I think it will make a good pad.
And that would depend,,, if you live in frost country, clay under a cement slab will freeze and expand.
What does it matter? Are you covering it with concrete? Did you proof test it with a loaded dump truck? That all we have here and it does Crack but generally it seems to be because it is not packed enough. I would not add sand. Use the machine to grade and pack it better. If you don't have a loaded truck you can check it with a probe rod, like a piece of 1/2" rebar, it should not go in more than 2 "s. Check the pad every 8"s as you make the lift. You might need to remove the fill and start over with the compaction.
I agree. I've never seen anyone here use clay under a slab. We always use a fine gravel pack. I have seen clay used against basement walls and it will crack the wall when it freezes and expands.
You can put a plastic vapor barrier on top of the clay. It will prevent the clay from drying out and it will prevent moisture from migrating into the cured slab. The lack of a moisture barrier is one of the reasons why many people have damp basements and crawl spaces under their homes.
It's just a pole shed with no slab but I've read that if the soil expands and contracts it will still cause problems. It might have been too wet when I was packing it.
same here we always use about 4 inches of gravel, and then some re bar, and pending size some relief cuts in it after it dry's
Can I ask how much fill did you put in? Did you put it in in lifts? I feel I would chew it up and let it dry. And compact it again. Clay will crack on top once the moisture comes out but have seen it pretty hard underneath. We have a lot of clay here, but usually underneath is shale so we mix it together. Makes beautiful fill.
I put it in in lifts but I think it was too wet and I didn't let it dry enough before packing. It's about 18-24" deep at the lowest spot. I'll dig it out and let it dry and then see how it packs. The clay was wetter than I normally work with. I don't think it would hurt to add a few loads of sand to it. More work but might as well do it right. I was in too much of a hurry to get it done. It's hard when you only have the weekends to work on your own projects.
you say it was like modeling clay was it really that thick and heavy and sticky around my area that is called bull tallow and you do not what it around any structures because it will expand and contract with the moisture conditions (dry weather/wet weather) the only time you can use it is if you can bury it at least 5' below footings or sub grade where rain water does not get to it. and then you need to mix it with either sandy, gravel or shell soils or you may be able to mix some dehydrated lime or bags of cement and mix it in that would be better than sand because it changes the chemical make up of the soil but if you do that better make sure to have it graded right before its dries because it will get so hard you will not move it
The problem with clay is that even if your pole barn posts are buried beneath the frost line, when the clay expands on freezing it will pinch hard enough to lift the poles from friction. I have two neighbors with pole sheds that have both gradually lifted over two feet over the last 20 years. Their poles were only buried 5'. One has added metal on the bottom but it is now sits crooked as all get out. I would not have clay around my poles it in any deep frost prone area. Many are now wrapping the poles with plastic so the frost slides easier. Not sure how well it will work long term. The best seems to be to use longer poles for more friction holding down below the frost line.
The poles are packed with 3/4" washed rock. I think I'll dig it up and let it dry out and start over and mix a few loads of sand with it.
That is my suggestion as well but we don't have to deal with frost down here. I have used ag lime and bagged cement to dry up wet clays in order to get the moisture right on a compaction test. Like Clint said it changes the chemical makeup of the clay. Now the deep frost in your area is another animal, something I have no experience with.
Compacted 2rc would make a better floor in my opinion. I used that as a base under my driveway and after compacting it was like concrete. So the one part of my driveway is as if it was 10" of concrete not just 5".
2rc is not a stone classification I am familiar with, what is it size wise?
As far frost pushing up pole barn poles or legs, I guess you guys are not are boring a big enough hole. Move up to an 18" bore on a 6" pole or a 24" bore on a 8" pole and use bagged concrete. Make them deep and rent a special bit that puts a flare in the bottom of the hole. Makes the hole kind of look like an upside down engine valve. This will keep the poles from pushing up. You can expect to use 1000 to 1800 lbs of concrete per hole.
The holes are drilled 8' deep and 16" dia. with a foot of concrete poured in the bottom and cured for a footing under the posts.
Its dirty 2b with sand. If I remember correctly.
#2 crusher run... cr. rc? 2 inch stone ?
"2RC is a modified stone which means it includes a variety of sizes and fines which are 2" and under. This product includes 5 aggregates and may have some clay or soil content. It is used in a variety of ways and packs well. It can be compacted for driveway beds and roadway beds, it is also used in water and sewer installation. It is sized at 2" and under." There was quite a but of sand with the stone I got.