ABSTRACT

This chapter deals with the geological and geophysical surveys used to investigate what rocks and soils are present, and how they are distributed under the site. A wide range of physical properties of rocks are used as the bases of particular geophysical methods. The most common in engineering surveys are: elastic properties, used in the seismic methods; magnetic properties, used in the magnetic methods; electrical properties, used in the electrical and electromagnetic methods; and density, in the gravity method. Surveys can be commissioned from specialist contractors, who may also offer geological interpretation of the air photographs as an additional service. A site inspection should be made as part of the preliminary geological exploration. The investigator should ideally have a copy of a British Geological Survey or other geological map to which he can refer. If a preliminary geological map of the site is not available, the investigator should attempt to make one.