Depth of piers set in asphalt? 1

[mjohn]

I want to build a deck supported on concrete piers over an existing asphalt (blacktop) yard which has an uneven surface.
In soil, it is advised that the minimum depth of the foundation for the pier should be the frost line (Boston, MA - 30"?).
Does this apply when the piers are set in an asphalt covered yard (as far as I know the layers beneath the yard are a mixture of gravel, builders waste and soil.)

 

[digger242j]

" ...as far as I know the layers beneath the yard are a mixture of gravel, builders waste and soil.)"

It sounds like you're on some amount of fill. One of the Geotechnical experts might want to render an opinion on whether you can expect that to present a problem as far as sufficient support for columns.

As far as frost is concerned, it was recently discussed in thread194-88791 , and the consensus of opinion is that frost will penetrate to a greater depth beneath paved areas than it will below landscaped ones. Given that fact, my suggestion would be to avoid any temptation to cheat on the depth of your piers, and even consider going a little deeper than the specified depth.