Just started a job, 700 sqft driveway. In a heavy clay soil. Driveway was previously asphalt so we removed that along with 15 inches of previous base and clay to provide a 12 inch gravel base. Put in 2 loads now up to about 8" of compacted base, the water seems to be moving up into the gravel. The base is spongy under foot and only another 4" of base remaining to put in. Suggestions. I'm thinking I have to go down another 12 inches or perhaps more, but how far do I take it and is there anything else that needs to be done.