Patio base from hell.

Hello everybody. Looking for some input on a problem I’m dealing with at the moment. I’m building a 25x25 paver patio with a 8x8 fire pit offset from the middle. 12’ on one side and 5’ on the other in both directions. The yard is sloped about 6” on 25’ one way and more or less level the other way. I rented a track steer to excavate the high side and over dug. And then it rained. The following day I put some of the mud back in, ran the plate tamper over it, and filled it with 4” of QP. Graded it and compacted it with the plate tamper.

At this point I learned about pumping soil and the difficulties of clay ! I waited 3 weeks to see if it would firm up and it didn’t. No change whatsoever. So yesterday we hand dug about 5 yards of QP and mud out of the soft spots. Everywhere else is really firm so we’re assuming that it’s good. It’s very tight.

Right now we are a good 12” below where the ground was before we started. The dirt is slightly mushy but nothing like it was. It felt like a waterbed before. We are definitely down to undisturbed soil.

I’m going to have 5 yards of fresh QP delivered this week and I’m looking for any advice to prevent this from happening again. I’ve read about spreading lime over the clay, I’ve also seen people recommend spreading Portland cement. Right now it looks like an empty koi pond so I’m sure it’ll rain and make it a mud pit before the weekend. I hate clay.

I forget the exact numbers but the high side is about 2” below grade and the low side is about 4-6” above grade. It’s pitched an 1/8” per foot going with the slope of the lawn and I’m going to crest it where the water will run into the fire pit.

We built the fire pit first by pouring a reinforced slab and stacking concrete blocks on the concrete.

Any thoughts on preventing soil pumping while compacting ?