UNDERGROUND EXPLORATION
Electric, electromagnetic and seismic tomography.

Presentation :
Since the beginning of the century, geophysicists have been proposing underground exploration methods based on different physical principles like the propagation of electric, electromagnetic or elastic waves, natural radioactivity, etc. Each of these methods can be distinguished by the physical processes involved. In order to propose more reliable and more precise underground exploration, DCI has specialised in the use of three types of geophysical exploration.

Objective :
Non-destructive investigation allowing access to a 3D image of the underground, with a view to identifying its internal structure like geological heterogeneity, stone walls, the depth and thickness of an economically exploitable layer, etc.

Application fields :
Environment
Search for water, followed by sheets
Geological map
Archaeology
Mines and quarries
Geotechnics

Electromagnetic tomography :
Based on the principle of electromagnetic induction and the measurement of surface EM field variation.
Particularly dedicated to the detection of large heterogeneity Chosen when no prior knowledge exists. Easy and quick utilisation. No sensor or artificial source needs to be installed. Resolution of about 10 metres, more in-depth resolution reliability. Maximum investigation depth of about 60 metres. Allows the exploration of large areas.

Electric tomography :
Based on the measurement of the resistivity of bodies buried underground after electric current injection.
Particularly dedicated to the detection of tabular and sub-horizontal layers. Chosen when no prior knowledge exists. Requires the installation of electrodes and sources of artificial current. Resolution of about ... metres, more in-depth resolution reliability. More than 100 metres maximum investigation depth. Exploration limited to small areas

Seismic tomography :
Based on the principle of elastic wave propagation perturbation by the geological components of the environment. Particularly dedicated to fine detection of geological structures. Chosen as supplement for prior explorations. Requires the installation of sensors and artificial seismic sources Resolution of about 10 metres, equivalent in the three directions. More than 100 metres maximum investigation depth. Exploration limited to small areas.

Example of resistivity cut :
EM, electrical data Or seismic data Establishment of acquisition profile in the field Underground visibility at all the desired depth Software dedicated to geophysical data processing and analysis D.C.I. has developed a software dedicated to the formatting, processing and analysis of the geophysical data gathered in the field. It is used to globally process a very large number of data from investigation areas, even if the profiles are not evenly distributed and even if topographic differences exist.

Editing the results :
The software provides a view of the underground, at all the desired depths (limited to the maximum investigation depth) and for all the points of the investigation area. The end result is a three-dimensional representation of the underground. A model of the explored volume may be prepared on demand.