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Geological discontinuities, main flow path and chemical alteration in a marly hill prone to slope instability: Assessment from petrophysical measurements and borehole image analysis

Authors

  • Johanna Lofi,

    Corresponding author
    1. Géosciences Montpellier—UMR 5243—CC 060—Bat. 22. Université de Montpellier 2, Place E. Bataillon, 34095 Montpellier Cedex 05, France
    • Géosciences Montpellier—UMR 5243—CC 060—Bat. 22. Université de Montpellier 2, Place E. Bataillon, 34095 Montpellier Cedex 05, France.
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  • Philippe Pezard,

    1. Géosciences Montpellier—UMR 5243—CC 060—Bat. 22. Université de Montpellier 2, Place E. Bataillon, 34095 Montpellier Cedex 05, France
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  • Didier Loggia,

    1. Géosciences Montpellier—UMR 5243—CC 060—Bat. 22. Université de Montpellier 2, Place E. Bataillon, 34095 Montpellier Cedex 05, France
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  • Emilie Garel,

    1. Université d'Avignon et des Pays de Vaucluse—UMR 1114 INRA/UAPV, 33 rue Louis Pasteur, 84000 Avignon, France
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  • Stéphanie Gautier,

    1. Géosciences Montpellier—UMR 5243—CC 060—Bat. 22. Université de Montpellier 2, Place E. Bataillon, 34095 Montpellier Cedex 05, France
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  • Christophe Merry,

    1. Géosciences Montpellier—UMR 5243—CC 060—Bat. 22. Université de Montpellier 2, Place E. Bataillon, 34095 Montpellier Cedex 05, France
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  • Karim Bondabou

    1. Géosciences Montpellier—UMR 5243—CC 060—Bat. 22. Université de Montpellier 2, Place E. Bataillon, 34095 Montpellier Cedex 05, France
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Abstract

Clay shale landscapes are sensitive to landslide, erosion, and re-sedimentation processes. In this context, tectonized clay shales have peculiar hydrological and mechanical behaviours. In order to improve our understanding of the processes involved in such systems, an experimental site has been settled in the Draix Observatory (ORE DRAIX) on a black marl hill slope of the Southern Alps (France) in the framework of the ECOU-PREF project. The site is a natural laboratory to study the evolution of clay shale landscapes at several scales (regional to µm). In this study, we aim to characterize the internal structure and fissure patterns of a stable interfluve, in order to locate preferential water flows within the system, and anticipate its evolution. This work is based on a series of mutli-disciplinary approaches including petrophysical analyses, well pulse injection tests and downhole geophysical measurements. Borehole geophysical results were combined with laboratory measurements on core plugs (permeability, density, porosity, and acoustic velocity). Optical and acoustical images have been used as an original tool for internal discontinuities characterisation and potential active flow path detection. They allowed the identification of three main lithological units interpreted as several stages of shale alteration. In addition, several main structural plane discontinuities (open fractures, schistosity planes, and fractures infilled with calcite or clays) were identified from the images and their potential transmissivity discussed with regard to piezometric and tracer measurements. In all, the integration of measurements leads to propose a simple scenario of fluid circulation and chemical alteration of the interfluve. Copyright © 2011 John Wiley & Sons, Ltd.

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