If you approximately double the footprint of the lift columns with a 1/2" steel plate, that should be safe enough, and probably less expensive than digging up the floor. That's what I plan to do with the 6" thick floor of my shop when I install a twin-post lift soon.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!