Water and clay don't mix!!

[RayH]

I think I screwed up my latest project. I was putting in a gravel pad for one of those prebuilt wooden sheds. The area where the shed is to go is slightly sloped so my project was to make it level. I used landscaping timber around the perimeter of the area. I had some dirt (mostly clay) and a couple tons of crush & run left over from another project. The one side of the pad had to be built up about 12" to be level with the other. I didnt have enough crush/run to fill the whole thing in so I put about 6" of dirt in and finished off with gravel. I rented a compactor and ran it over the dirt and gravel as I was filling it in, along with running over it with the tractor. When I was finished, it was solid as concrete, or so I thought. After it sat through several inches of rain an a couple days, it has become like a waterbed. It hasnt really compacted much but its mushy and bouncy, if I jump on it, my wife, standing 2' from me will bounce. Now Ive got a shed on the way in a couple days and my pad is a waterbed. I dug the crush/run off the top the other day to help the clay dry but its still sticky and unstable.
Does the dirt need to come out? Will it eventually dry and stabilize? I've done projects like this before but never had this problem.

 

[zeuspaul]

You cannot compact clay. You can conslidate it by putting a heavy load on it and waiting a loooong time.

Remove the clay.

Zeuspaul

 

[EddieWalker]

I disagree, clay compacts realy, realy well. In fact, when you get it right, water will shed right off of it!!

What I think happened is you did a bad job of compacting it and created a sponge. Either you did it in too large of lifts for the compactor to handle, you didn't spend enough time working it or in all probablity, the clay was too dry.

You didn't mention water content before you started. If you don't have enough moisture in your soil, nothing will compact it. NOTHING!!!

When it rained, the clay soaked up all the water and now it's "pumping" or feels like jello.

You can try to wait it out, but it's a very, very long process for it to dry out.

What I'd do it pulle it apart, spread it out over a large area and let it dry out some. Again, don't let it get too dry. You want enought moisture in it so the when you take a handfull and squeeze, it will stay together. If any moisure comes out when you squeeze, it's WAAYYY to wet. If any dust or crumbs break off, it's too dry.

Most construction sites have water trucks on hand for this very reason. To mix fill material that is dry to a consistancy that it can be used and compacted.

Good luck,
Eddie

 

[RayH]

It was dry when I filled with it. Dry enough that it was crumbly when squeezed.
Its much better today after getting some sun and air to it and it has compacted a little more. Its about an inch lower than it was so I believe you may be right about it being too dry and me not doing an adequate job of compacting it.
I'll tell the shed guys to deliver Friday, that should give it time to firm up.
Now that its soaked up plenty of water and been compacted some more, do you think it will be fine to place the shed on or will this continue to happen?

 

[EddieWalker]

There's a fine line between enough moisture and too much. Trying to guess when it will be at the right point after full saturation is beyond my ability. I would estimate it to take at least several months to dry out enough to put a shed on from what you've said.

Lets look at it from the shed's perspective. What type of foundation does the shed have? Your pad will continue to dry and settle for a very long time unless you redo it. If you put the shed on it now, will the foundation be able to distribute the load over an uneven, or settleing base? Can you remove the shed in a year ot two and redo it then?

Just so you don't feel so bad, I did something similar while filling in a hole from a stump. I used dry powdery dirt for fill. A week or so after a heavy rain, I was driving my dozer over the area and went across the fill for the stump. The dirt had turned to quicksand and swollowed my dozer!!!

When worked right, clay is a wonderful builing material for allot of applications. When worked wrong, it's the most miserable stuff on the planet!!!

I think you need to pull it apart and let it dry for three or four days and then rebuild the pad on thursday in small lifts. Then drive over each lift with your tractor over and over again until it's solid.

Eddie

 

[MarkV]

Just a thought here. The shed is going to keep the water off the pad so the pad is going to dry out eventually. Most of the pre-built sheds I see have a plywood floor and are often set on corner blocks for leveling. Even if the shed is made without a floor so the gavel is the finish floor can you set some concrete blocks filled with concrete at the corners and maybe mid span of the walls to support the structure? If the pad settles another inch or so more gravel could be added in the future to keep it level with your supports.

MarkV

 

[Renze]

I dont have any experience with clay, our soil is different: When it's dry, we have to keep spraying water on our sandy (dust) soil. When we want to build, we just dig 2 feet and pour concrete on narrow slabs, to carry a 21x50 meter horse riding hall.

Luckily we dont have these issues when building, but i thought of what they do, some miles away from here: just make a pole foundation. If you dig some pits down into the white/yellow subsoil (i dont know which colour of subsoil you have in your area but we have bright beach sand at 3 to 4 feet deep) and place 8" cardboard tubes in there to use as pillar castings, you can make a pretty solid foundation. Afterwards you can just pour the slab over the heads of these pilars to create a bridge. If you have a steel or wooden building, you dont even need slabs if you put a concrete pillar under every pole. Having the pillars down onto deeper soil layers, you require less bearing area than a slab on topsoil.

 

[Egon]

Pull off the gravel and added clay. Then dig out the topsoil and start over.

Clay does not compact well with flat vibratory type packers as they layer it and do not bind it all together. Needs something like a sheeps foot or similar type packer that can have vibratory assist.

For packing to check for close to optimum moisture in the clay take a handfull and roll it between your hands. If it crumbles it's too dry. If you can make a nice pencil sized roll its about right. If the roll just keeps getting smaller without breaking it's too wet.

For small areas a jumping jack compactor will work. Just remember to guide it rather than have armstrong control. All that does is make you weary.