Characterization of Textural and Hydric Heterogeneities in Clay-rock with Induced Polarization Method (Aveyron, France)

The extension of the excavation damaged zone (EDZ) has been investigated thought electrical resistivity and induced polarization methods in time and spectral domain from three galleries belonging to the French Institute of Radioprotection and Nuclear Safety (IRSN)’s experimental underground research laboratory of Tournemire (Aveyron, France). Combined electrical resistivity and Induced Polarization methods show the possibility to delineate textural changes associated to desaturation of the clay-rock induced by the ventilation of galleries. The impact of the desaturation is particularly observed on the gallery’s walls. In addition, Time domain induced polarization indicates the presence of mineralization (e.g., especially pyrite) located in the structural discontinuities such as tectonic fractures (mm-cm), tectonic fault (m) and calcareous nodules (cm). We cannot see these nodules on the resistivity tomogram because the contrast in resistivity between these nodules and the matrix in which they are embedded is too low. Also, the resistivity tomograms do not allow distinguishing between the calcite-filled tectonic fractures and the new fractures which are associated with the mechanical damage (both of them show high resistivity values).New fractures and hydric fractures associated with hydric changes of the formation exhibit low values of chargeability.