MJ wrote:
I am building a pole barn and am ready to pour a concrete slab. The structure has been built on a slight slope so I had some dirt fill brought in and compacted. The deep end of the fill goes down about 30". The frost line in my area is 4'. Is it possible to drive rebar down below frost line, then bend it over into the concrete to prevent possible settling later on?

Answer:
Thanks, MJ for the question. Driving rebar into the soil is a big NO-NO (though many contractors do this when placing rebar in footings). Remember, the rust process is electrical (called oxidation). When you drive rebar into the soil, you provide an "electrical connection" to the ground through which electrons may flow. The result... RUST IN THE REBAR. When rust is allowed to continue, the rebar will expand (rust expands to 1,000 times the original steel volume) spalling the concrete and accelerating subsequent oxidation. You've got to get the bottom of the footing below the frost line, not to prevent settling, but to prevent frost heaving the footing upward. If it's interior space, you should also provide some rigid board insulation between the sides of the footing and the soil. This limits cold concrete inside the building that can lead to some real heating problems! Sounds like you need a properly designed concrete sub-wall (30" above the ground and 4' into the ground). You must be way north of the Mason-Dixon line!