The foundation is a crucial component for ensuring stability of a structure and is often viewed as being equally important as the human hands and feet to the body.
In the built environment, man-made structures such as houses, apartments, schools, stores, bridges, highways, parks etc., are supported and anchored by their foundation. The foundation of a structure transfers its weight into the ground. Two main types of foundations are shallow foundations and deep foundations; a shallow foundation is constructed relatively close to the ground level and transfers the structure’s load to the earth very near the surface whereas the deep foundation transfers the load to a greater depth.
A major factor which contributes to the decision of whether to design and construct with a deep foundation or a shallow foundation is the soil type. Some soils are very strong while some are weak or marginal. Strong and firm soil gives better support to structures.
Building in an area with a high water table also affects the foundation type given external hydrodynamic effects. E.g. Portsmouth, Dominica generally displays a high water table (relative to ground level) and therefore the foundation would need to assume a greater area for shallow types, for improved stability against upthrust and other effects.
What is seen, especially by a layperson, on the surface of the soil sometimes is not what is 15 feet below – top soil may appear to be soft and weak but after digging to a certain depth may show otherwise, and vice versa.
It is important to consult a structural/civil engineer to provide advice and or design the foundation that is right for your land type and load of your structure. Remember, building a foundation is expensive so it is more economical to do it right the first time and avoid costly foundation repairs.