In the event that the site you choose to build upon has poor soil conditions, you have alternatives. There are several methods that you can employ. However, I highly recommend that you consult with a competent structural engineer to assist you. The calculations which are required to determine the proper structural alternative can generally be performed only by a trained professional. Do not attempt to do this by yourself!

One method to consider is the use of "piles." Piles are structural elements (steel columns, wooden timbers, etc.) which are mechanically driven into the soil. These elements act in soil much the same way as a nail acts when driven into wood. The piles attain a certain "skin" friction as they are driven into the soil. The deeper they are driven, the more friction they produce. You can illustrate this very easily. Drive a small finish nail 1/8" to 1/4" into a piece of pine. Generally, you can readily pull this nail out with your fingers. Reinsert this nail into the same hole, and now drive it 1" to 1 1/4" into the piece of pine. I think you get the picture. When the pile is driven sufficiently deep enough, it attains enough friction to hold the weight of your structure.

Another structural alternative is a pier. Piers are simply columns. They are created by drilling a shaft in the soil until you reach a layer of rock or soil which will be strong enough to support the weight of the structure. These shafts are then filled with concrete, usually reinforced with steel. Generally, a specialty contractor with very large drilling equipment is required to perform this work. It is risky and dangerous. The shafts can be very deep and the sidewalls can collapse without warning if unsupported. Drilling piers is not to be performed by an amateur.

Structural engineers can offer even more alternatives given your specific soil conditions. You will never regret hiring one. They can relieve your anxiety. In a difficult building situation, only a fool would proceed without the advice of a competent engineer.