to answer OP his question about the big size rocks: NO
You will only, just as you are doing now with the smaller size rocks/gravel, push it in the clay.
Your problems sound very familiar.
I agree on the geotextile things but just dont see how good it will be fighting with that truckload. I would never use it for driveways.
We have similar problems in our region and it is a habbit to order a load of clean gravel every year after winter to top dress our driveways. Just, i'm an immigrant here and i hate topdressing with $$$ every year (even more as i do hate the manual labour involved with gravel). So, i did it a little different.
We rented a backhoe and took about 10" from the top layer (so the muddy stuff was gone and you are back at firm clay level).
We then dumped in the most unwanted mix of rocks, gravel and stonedust. This is the stuff nobody wants and much cheaper than a nice calibrated mix.
The point being that this rough mix makes for a very hard layer which does not allow water to go flow through but stay on top of it. (so ask for a lot of dust in your mix) and because it settles as a crust it also spreads the load more evenly.
If you can grade this mixture a bit you are making a flowdirection for the rainwater. (or you put your drainage tubing under this layer if you have groundwater issues)
then we added mix on top, like 3", as a finishing layer. (there i used small pebbles and gra as you can grade them much easier, that was also an unconventional move)
When it was raining the water flowed through the toplayer and then on top of the mix layer to the sides of the driveway.
If you allow water to go to your clay layer it will weaken the clay and thus allowing the clay to absorb any toplayer when you put pressure on it.
When we build our house and had to put pavement for a parking and driveway the construction company took off the 3" and left the bottom layer as it was. He could not make it a better underlayer, only make it worse.
Oh, and needless to say that all types of gravel consisting of round shaped pieces (pebbles) are a no-go as they never stabilize.
2cents only
