Compacting the ground in the driveway with which material?

Hello,
I had a large amount of gravel 16/32 mm leftover and spread it in the driveway 3m wide and 10m long to create a firmer surface. Unfortunately, that didn’t really work. Even compacting with the vibrating plate doesn’t provide enough firmness.
Now I’m considering maybe adding clay or another material, e.g., rolling it in or slurry-coating to stabilize the area.
Does anyone perhaps have another idea or advice on how to stabilize the area?
I’m grateful for any tip.
Best regards
Michael

Buy a time machine and inquire about the compaction before installing filter material. Applying new material as a replacement for the missing zero line makes sense mathematically, but in practice I only see it as partially advantageous, because you then also have to mix the mixture. Just slurrying, my gut feeling says, is not enough. For a footpath, okay. Under vehicle load, it is not permanent. Maybe it is better to invest money in the substructure now, then the driveway will last longer.

Which soil is to be found beneath the gravel layer? How high was the gravel layer installed? This of course is all pointless if the soil underneath is not sufficiently load-bearing. Many soil reports do not recommend replacing several meters of soil before a base layer can be installed for no reason. When setting angle stones, we encountered such a clayey, permanently wet layer. I had it excavated on a large scale and replaced with gravel.