120 A new concept of karst development based on hydrogeology and geophysics The primary objective of the electrical resistivity panels was to investigate the electrical signature of these layers. Vertical resistivity panels were implemented in five boreholes: M20, M04, M08, M07, and M11 (Fig. 1). Material and method Electrical prospecting (Chapellier, 2001a) is a non-destructive geophysical method used to determine the structure and quality of the terrain. This method is based on the ability to represent the nature of the terrain in terms of one of its physical parameters: electrical resistivity. The resistivity of geological formations primarily depends on the following factors: • water and clay content; • composition of electrically conductive minerals, such as sulfides (pyrite, galena), iron oxides, graphite, gold, and silver. In boreholes, the Electrical Cylinder Method (Lantier & Frappin, 2000), developed by Soldata Geophysic (now known as Sixense Geophysics), is a technique Figure 1 Location of boreholes at the Poitiers HES site, France. Red circles indicate the boreholes selected for electrical measurements.
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