Replacement of soil makes sense for drilled shafts but not for driven piles. For driven piles you should add pile weight, particularly if you are using lower factor of safety.
Depends on your purpose but you can look at AASHTO LRFD Bridge Design specifications or Hoeks corner at the following link:
http://www.rocscience.com/education/hoeks_corner.
I am working on a project where embedment depth for existing bridge foundation will be reduced. This is third such bridge that we have seen in the recent past. Anybody has any experience with protecting the footing subgrade from frost? Thanks.