My deck has 6"x6" wooden support posts sitting atop 12" diameter concrete footings. The tops of the concrete footings are about 16" above grade. When I inspected a little below grade, I discovered the 12" diameter footings end just 2-3 inches below grade, but they seem to be poured on top of 6" diameter concrete footings. The 6" footings completely underground, and have an unknown depth. The deck over the posts shows no sign of settling/heaving however, and the deck appears to be at least 10 years old.
The wooden posts appear to have no attachment to the 12" pillars: one of the posts has shifted to the edge of the 12" footing. I would like to attach the posts to the footing using a rebar post holder by drilling a hole in the center of the footing, and using epoxy or some adhesive for the holder.
My concern is that the footing may crack during drilling. Is this much of a risk for a concrete footing this size?