From an engineering viewpoint, the ground beneath a site can conveniently be divided into the categories shown in Table 2.1, which are based upon generalizations of its expected behaviour in construction works.
These broad generalizations are, of course, limited in accuracy. But they give the geotechnical engineer a good basis on which to consider, at the start of a project, both the likely construction problems and the methods of investigation which might be used. In practice, it is found that the ground varies continuously beneath a site, and it is not often possible to find sharp transitions from one type of material to another. This then, calls for more refined, systematic, description and classification of soils and rocks.