I'm in Texas, so things will be different, but the basics are always the same.
First thing you need to do is have your pad leveled. Sounds like this is what your doing. You have two choices.
But first a littel about dirt. Virgin soil that has not been disturbed is considered good for building on. There's all types of soil and some is better than others. Clay is generally considered one of your less desireable soils because of the amount of movement you get out of it.
Clay will crack when it dries out and expand when it gets wet. All that movement leads to a cracked foundation.
Fill dirt will aslo settle over time. It takes an aweful lot of effor to get it compacted, and driving over it with a tractor aint going to do it to the level of undesterbed soil.
When you build up with dirt, there is always going to be a spot, and sometimes many places, that don't get totally compacted. This becomes your weak area that may settle over time. It could take 20 years, but sooner or later, it will settle and you're slab will crack, your house well settle and all sorts of things will happen.
This is the basic broblem with most cracked foundations. Of course, it doesn't cover them all.
Now to your situation. If you have the land and space, it's better to cut down the high spots. Make sure you still have drainage, cause water getting under your foundation is the biggest reason the dirts settles and moves after everything is built. Water is your number one enemy. Get it away from the house !!!
To level off the pad or build it up, use sand. Builders sand is a course, clean sand. It spreads easy and doesn't need any done to it to build on. Some parts of California, where earthquakes and building codes are extreme, require so much sand under a slab foundation. I think it was four inches, but don't remember for sure.
With rebar and good concrete, you don't have to use sand under your foundation, I didn't on mine, but I did on another house I built last year. Your code and local conditions will also dictate on what you use. Just ask around.
Eddie
