I would be concerned about top soil under my drive way. Especially more than 6" freshly put. I don't know what soil you have but even then more than 6" needs to go back in "lifts" not more than 6" at a time and compacted to 90 to 95% of original (of recommended density material) Check this out for basic information on the subject:

http://www.concrete-catalog.com/soil_compaction.html

A proctor test will determine the compaction/density of the soil you have. Might want to do that to see is what you have can actually be compacted sufficiently for concrete overlaying.

BTW, I did stay at a Holiday Inn once...

Good luck,