What you have is a deep beam. See the deep beam provisions of ACI 318 chapter 11. Traditional shear and flexure analysis methods aren't really valid, but the footing still needs minimum reinforcing. Also, probably not necessary due to the small loads, but consider checking the solution with a...
Fresh concrete does not have a uniform constitution through its thickness after being placed. Water and air entrapped below the reinforcing bar decreases bond more for "upper" bars than for bottom bars (bottom 12").
Consider industrial slab support via ground improvement, such as soil-cement columns, geopiers, or stone columns. These systems have no rigid connection to a structural slab, but are hard points and a typically very weak soil. Say a geotechnical engineer or design-build contractor proposes a...
