The asphalt material is slightly pliable. The surface underneath needs to
be a hard compacted surface -- I think it is compacted modified stone (or
something like that). That creates a solid surface for the asphalt
material. The first layer of asphalt material needs to also be compacted
with at least a 5,000 pound roller and is called a stabilizing layer. Then
a second coat of asphalt goes on top of that and is compacted.

Bob wrote:
Hello,

Was just wondering about this.

It is pretty well accepted, apparently, that a new asphalt driveway
for a residence should be laid over about 4" to 6" of gravel.
Never over soil directly.

Why ?

The hot, liquid, asphalt I would pretty much think makes the gravel
into one, solid, "clump" underneath (the asphalt).
So, it's hard to see that any improved drainage results.

Increased "stability" perhaps ? If so, how ?

So what does the gravel add as a benefit over just laying the asphalt
on top of well compacted soil ?

Thanks,
Bob