Originally Posted by ncor
core your slab have an engineer inspect the house, basement and concret core then closely adhear to his recomendations.
Drilling a hole in the footing area / floor will determine depth, and overall condition will suffice. Actually drilling a core sample would be great, but what exactly will you use for a comparison? Aged concrete is notorious for being harder then a woodpecker's lips, and may break with a strength of 10,000 psi, but may shatter under a load also. The overall condition of the concrete, depth where the lally collumns would be placed, and weight supported will determine if this is feasable.