I've been searching the net as well as this forum but haven't found any info regarding this idea. I plan on pouring a shallow footing (w/rebar) for a mortarred rock wall. I am in a cold climate and was thinking of incorporating column/pier footings that extend below the frost line with bulbed/coned bottoms. I am hoping this will prevent frost heave cracking of the footing and subsequently the rock wall. Any comments or suggestions appreciated, thanks.
If you are in a frost heave area and water gets under the wall it seems it will still go up even if the footings stay down if I understand what you are talking about.
The best way to do what you are suggesting would be to do the column footings down to below frost line and then come up to just below the final grade and tie them together with a grade beam (concrete reinforced horizontal beam with rebar tied into the footings). The soil under the beam should be removed (if clay) and replaced with drainage material so it won't freeze and lift the beam.
You could then either face the grade beam with stone and bear directly on it, or build a structural rock wall on top of the grade beam.