Foundation is used to support a building or structure and transmits loads directly to the underlying soil or rock. It must satisfy two fundamental requirements. Firstly, it must provide an adequate factor of safety against failure of the supporting strata. Secondly, any resulting settlement, and in particular differential settlement, should not be detrimental or interfere with the function of the structure.
Shallow foundations are constructed relatively close to the ground level. Shallow foundations can only be used where the soil at that level is capable of adequately supporting the load. A deep foundation is used to transfer loads from a structure above ground through upper weak strata of soil to a more competent one at depth, beyond which shallow foundations become both impractical and uneconomic.
The type of concrete foundation depends on the area the foundation will be located on, and the type of structure that will be placed on it. Adjustments to the form of a foundation based on the footings cannot be made after concrete is poured. Because concrete is very heavy, one should be sure that the formwork is strong and firmly in place. The foundations should be covered from rain as it can cause depressions in the concrete and cause your foundation to be uneven.
Regardless of the type or how you build a concrete foundation, the most common problem facing homeowners and contractors is a concrete foundation crack. A concrete foundation crack is perfectly normal as 66% of all concrete foundations crack within the first year. The major reason for cracks is concrete shrinkage and a settling concrete foundation.
The primary design concerns are settlement and bearing capacity. When considering settlement, total settlement and differential settlement is normally considered. Differential settlement is when one part of a foundation settles more than another part. This can cause problems to the structure the foundation is supporting. Foundations are designed to have an adequate load capacity with limited settlement by a geotechnical engineer, and the footing itself may be designed structurally by a structural engineer. Inadequate foundations in muddy soils below sea level, are a primary cause for houses to subside.
Remember, you only get one chance to protect your home right the first time. Do it right, do it once, do it forever.