So I had a contractor give me a quote on installing a concrete driveway. He was sketchy with some of my questions, so I doubt I'll be using him regardless. But in particular, I asked him how far down he would excavate down to install the driveway. He said he would excavate down to 4 inches (wtf!) then compact and level. I asked him why so shallow, and he said because it was gravel already and packed down by years of parking cars on it (15-20 years), to excavate, replace the gravel and pack it down again was pointless. I asked him "how do you know it's gravel all the way through" (I suspect it's just gravel poured on top, then clay soil underneath), he said he would judge it when they start excavating, if it's not, they would dig up to 4" deeper. So he was planning on excavating to 4" deep, compact, level, rebar, than pour 4" of concrete. I believe it will be done in 3 sections, to match the original driveway. The area is a 10' x 22' gravel pad. There is a large deciduous tree in the neighbor's yard located approx 10' away (branches extend all the way to the far end of the gravel pad), so I was a little concerned there might eventually be roots heaving under the driveway. There are also neighbor's bushes lining the driveway. My question is how would you install a concrete driveway in this situation? Is there some merit to his excuse for such a shallow depth?