Geological classification
Nature and classification of soils

In geology as applied to construction, a fundamental distinction is made between "terrains en place" and "terrains d'apport". Soils in place are those in their original geological context, while fill soils are those displaced or deposited by natural or man-made processes. Generally speaking, and barring specific exceptions, imported soils are considered unsuitable for foundations, as their stability and behavior under load are not as predictable as for in situ soils.