Geophysics applied to civil engineering

Geophysics applies the tools of physics to the study of ground structure. It is carried out from the ground surface (surface geophysics), in a borehole using a probe carrying measuring instruments (logging) or between boreholes, borehole and surface, borehole and gallery (borehole geophysics). This is one of the approaches used for geotechnical reconnaissance of a site prior to the construction of a structure (building, urban or transport infrastructure, dam, etc.). Geotechnical reconnaissance of a site involves determining the nature and distribution of the materials of which it is composed, and determining their properties. These elements are used to specify the location or layout of the structure to be built, to design its foundations and to decide on construction procedures. A large part of the reconnaissance work is related to hydrogeology, and in particular to the structure's relationship with water.

A geological model is created as part of the reconnaissance process.

A geological model is a set of representations of a site in its various aspects (nature, distribution, properties of the materials that make it up). These representations can take the form of maps, cross-sections, block diagrams, borehole cross-sections, texts or even models.

Initially, reconnaissance is always based on an initial geological model, which may be very sketchy, imprecise or unreliable. The aim of reconnaissance is to improve it, to make it reliable, precise and as complete as possible, so as to enable the design of the work to be based on the data we need and which are as reliable as possible.