Identification and Characterization of Hard Rocks Weathering Profile by Electrical Resistivity Imaging
A. Portal, P. Belle, F. Mathieu, P. Lachassagne and N. Brisset
Event name: 23rd European Meeting of Environmental and Engineering Geophysics
Session: Monitoring and Characterization of the Shallow Subsurface A
Publication date: 03 September 2017
Info: Extended abstract, PDF ( 918.14Kb )
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This study proposes an original method for the detailed characterization of the weathering profile in hard rock (plutonic and metamorphic) contexts by electrical resistivity imaging (Electrical Resistivity Tomography – ERT). The main objective is to identify the electrical signature of the different layers constituting the weathering profile, more specifically that of the laminated layer. Location of the latter is an important issue for geological (saprolite thickness assessment) and hydrogeological (location of productive boreholes) purposes. The dual approach presented here firstly focuses on real datasets obtained from field measurements acquired in both granitic (1 site) and metamorphic (3 sites) environments. Then, synthetic modeling, based on real data results, were performed in order to test the sensitivity of the ERT method to identify and characterize the layers of the weathering profile depending on the geometry (thickness) and the resistivity of the laminated layer and the Stratiformed Fractured Layer - SFL. The results so obtained highlighted for the first time (i) the complex electrical signature of the weathering profile, (ii) the resistant nature of the laminated layer and (iii) a resistivity gradient at the base of the SFL.