Sounds like a good idea to me. The roots will eventually rise to fill the new area. There could be some problem with having the old roots deeper but I can't think of anything off the top of my head. The dirt next to the plant stems should not matter.

Scott

I would worry about the TC blackberry. The canes grow from a single established crown. It might not be able to handle an additional 8 inches of soil dropped on top of it. But I really have no solid info or experience about that. And on the other hand, they are very strong growers and might laugh at the additional topsoil.

I would worry less about the raspberries that will sucker up from practically any bit of root.

Thanks! Yea, I figured the raspberries would be fine. They are pretty crazy... sprouting up in my lawn and what not.

I would not worry about the Triple Crown. I cover mine with at least 6" of wood chips and horse manure and have no problems; this eventually turns into soil.