I would probably figure out where your top of foundation is relative to existing ground. If you have 8' stem walls on a 12" deep footing than only fills > 9' should be of concern. I'm not saying that I would just bomb the dirt in, just that a concrete slab distributes the weight over a larger area than a footing with less loading. In other words a lower bearing is required for the floor slab than the foundations. But I wouldn't hesitate to call a local engineer, they are cheap and their experience can prove invaluable. A proctor test is only $150.00, field techs 85-100 per hour and the engineer shouldn't be more than $150.00/hr. For what you're describing, you could get sound engineering advice and support throughout the project for probably less than $2,000.
On another note, remember, a proctor only tells the maximum unit weight attainable by a material type, not it's bearing capacity. I could get a proctor on topsoil, doesn't mean I would want to build my house on it.
Finally, if I were you I would just hire a reputable local contractor. Not that I don't think you can handle the project, but they have the time, experience and insurance required to do the job right. Also with the market the way it is, contractors around here are doing work for just fuel and wages. You probably can't rent the trucks, loader and compactor for what they are willing to run their own for.
Best of Luck, Sounds Like a Fun Project.
On another note, remember, a proctor only tells the maximum unit weight attainable by a material type, not it's bearing capacity. I could get a proctor on topsoil, doesn't mean I would want to build my house on it.
Finally, if I were you I would just hire a reputable local contractor. Not that I don't think you can handle the project, but they have the time, experience and insurance required to do the job right. Also with the market the way it is, contractors around here are doing work for just fuel and wages. You probably can't rent the trucks, loader and compactor for what they are willing to run their own for.
Best of Luck, Sounds Like a Fun Project.