Improving Clay Soil

I am doing some improvements in my slightly sloped backyard which includes retaining walls, installing a concrete patio, and building a single car garage. I am not a heavy equipment operator, but am in the commercial concrete construction industry. I had to regrade the yard because the previous owner backfield against the back fence. During this process I uses a skid steer and mini excavator and discovered that my entire lot is clay. It had rained a few weeks before and the clay was deeply saturated but dry on the surface. Needless to say grading was sloppy due to pumping soil. So I got everything as close as I could and let it sit to dry for a few weeks.

I had someone come and haul off some extra spoils and the soil still pumped a little, but not as bad after drying. I cannot dig my backyard down to suitable soil and then backfill. It just isn't feasible for me. What are some methods to improve the soil for a patio slab and garage slab/footing?

I have heard of some people compacting rip rap into the soil with a jumping jack. Any thoughts or ideas that would improve the soil enough without breaking the bank? I do plan on putting base rock under the slabs. The garage slab will be 6" thick with a 12" thickened edge at the perimeter. I do overthink things a bit as I am used to building very large commercial structures where any pumping would be absolutely unacceptable. My gut says I can have some pumping for this home project, as the loads are low. Any ideas or thoughts would be appreciated. Also when the soil is dry on top and I probe it with a simple T handle solid pointed probe, it gets pretty hard at the surface.

Thanks.

How about using some bagged lime or bagged dry cement for soil stabilization? Till it in with a good big tiller on a tractor, then compact it and build from there. I do not know how much to use. You would probably have to ask a soils engineer about that.

I second the lime. Or better yet some CodeL if you can get your hands on it. Mix it in good and run a compactor over it.

Geotextile will help too. A thick fiberglass fabric blanket installed under your base material will prevent it from migrating into the clay. It will provide some additional stability

You're in California, Mowingman is in Texas, and I'm in Wisconsin, what we would do might not make any sense at all with your soil. Get a soil map and see what you're dealing with, under "engineering limitations" or something similar.

My first thought is calcium, but I've heard of some bizarre clays out there too.

I agree with Steve - geofabric or geogrid will be the easiest and cheapest solution for a light loaded residential structure.

A Mirafii N series fabric or geogrd if you want even more strength under your base rock. A layer of geogrid over the existing soils then a 1' layer of base rock compacted would be overkill.

I've got more on the subject but gotta run.

Get a soil sample: Plugs of soil about 4 inches deep from different areas. You can carve out some slivers with a hand spade if you do not have a probe. Put them all in a bucket and mix them up. Take that to your county extension office. They will send that off and recommendations will be mailed to you. Do not go crazy but work on what needs help.
Soil grows, at a rate of maybe 1 inch every 100 years, but clay is closer to a brick and needs some help. Best inexpensive help is plants growing in it. Plant whatever grass or grasses you desire with an annual such as millet or wheat depending on the season.
I know that is not what you want in your lawn but they have aggressive root systems and help hold the soil. Being annuals they dye and their root systems break down. These systems grow microbes as they dye and make pathways for your desired grasses.
A couple places that were most difficult worked out with shavings and manure from horse stalls broadcast over the top with new seed. They had already worked up like a garden several times. Had grass growing and dried up to one large dead brick. DOT would not release the bond until they approved the sod.
Overseed a time or two with something that disturbs the soil like an airator. Retest, water and it should be great with a bit of time and not a whole lot of money.