/diy/ - Do It Yourself

>>1549654
Oh boy. This is like an entire semester of soil mechanics and materials classes worth of shit to go over, but I'll try to dumb it down to the absolute basics.
tl;dr Expansive soils cause 2 main types of issues, uplifting or shifting. The problem is the solutions to each are different.
*TYPICALLY* the issue is uplifting, especially on clay soils.
Adding to that, problems typically come from the wetting and drying cycle. The biggest problems come from soil that can't stay either consistently wet or consistently dry.
So this a very YMMV situation and you need to know what the soil in your exact area tends to do. The short of it is, you need an engineer who knows your soil composition and expected loading to tell you anything ...concrete (ehehehe...)
To try to answer your questions generally:
>1. Would building deeper footings help?
You can probably forget footings all together because the worst problem you're going to get is going to be from differential settlement across the slab. Footings exacerbate that because you're localizing your load to different parts of the slab, so when one footing starts sinking but the others don't (or worse, rise), welcome to crack city, (bitch).
>2. Would excavating a certain amount of soil around the foundation and replacing with a less expansive soil, or gravel, prevent any problems?
The short answer to this is probably but only marginally, but the more accurate answer is that it's going to depend on the foundation type you end up with. If you're having issues with unstable soil, especially from wetting and drying cycles, you're probably not going to be able to excavate deep enough to get to stable soil. For footings, it won't do shit.