High Resolution Electrical Resistivity Tomography in Superficial Limestones at Tournemire Site, France

Abstract

Deep argillaceous formations are considered in many countries as potential host media for high-level long-life radioactive waste due their confining properties. The precise sedimentary, structural and hydrogeological characterization of such potential host sites is a key point in determining their appropriateness for the long-term deep underground disposal of radioactive waste in geological formations. The presence of faults in clay–rock formations should be carefully assessed, since these features could modify the confining properties. This study focuses on testing the potential of the electrical resistivity method to detect fault or fractured zones in the near subsurface layers above an argillaceous formation. We present in this paper results from a high-resolution electrical resistivity survey carried out at the IRSN Tournemire Experimental Platform (TEP). The electrical resistivity profile was located transversely to the fault and fractured zones location, inferred from geological data, that affect the Jurrassic formations at the TEP. Electrical resistivity data were successively acquired with 8m, 4m and 2m-electrode spacing. This multi-resolution acquisition allows to investigate the near subsurface limestones and dolomites to a depth of 100 metres. In particular, two sub vertical conductive corridors reaching the surface through higher resistive layers are correlated with fractured zones.