Caractérisation multi-échelle du milieu karstique non saturé.

Abstract : The karst environment and especially its superficial part is typified by an important alteration. At the Lascaux site, alteration is responsible for plate limestone and also detrital clayey-sands soils due to dissolution of limestones. The presence of painted caves in this altered environment raises the need to characterize the karst environment in order to protect the caves and contribute to mural paintings conservation. The aim of this PhD thesis is to characterize the karst environment at different scales using two main methods: (1) geophysics and in particular Electrical Resistivity Tomography (ERT) and (2), petrophysics at the Lab scale, including microscopy, mercury porosimetry and electrical measurements. At the field scale, we characterized the calcareous surroundings of the Lascaux cave relying on a 6 years-long time-lapse monitoring by ERT complemented by geostatistical 3D reconstructions of the resistivity values. The time-lapse monitoring permitted a better understanding of the hydrogeology of the site. Combining ERT time-lapse monitoring, 3D models of the resistivity distribution and additional measurements on samples allowed to identify a drain within the epikarst, which is most likely responsible for the emergence of water at the Lascaux cave entrance. The 3D modelling of the resistivity values also allowed to identify a scarp of unaltered limestones, northeast of the Lascaux cave, leaving room for clayey-sand detrital formations. In relation to a current research program on the Chauvet-Pont d’Arc cave, an original micro-ERT acquisition layout was fitted on the wall of an underground quarry, allowing measurements at a sub-metric scale with a centimetric resolution. At such a fine resolution, an unwanted electrode effect appeared. We remedied this electrode effect by inverting ERT data with an Equivalent Electrode Point (EEP) buried in the ground at a characteristic depth. The quarry wall was subjected to fires. Relying on a micro-ERT time-lapse monitoring during few months complemented by petrophysical analyses, we showed that the fires impacted the first centimeters of the quarry wall whose porosity and connectivity were modified. We also showed that seasonal water saturation variations could be detected at such a small scale. Thus, this small scale acquisition layout may ultimately be used at Lascaux to measure and predict water intakes directly at the cave walls in relation, or not, with the water flow modelled at the field scale. Such an approach may become a new tool for the conservation of painted cave walls.
Complete list of metadatas

Cited literature [170 references]  Display  Hide  Download

https://tel.archives-ouvertes.fr/tel-02303051
Contributor : Abes Star <>
Submitted on : Wednesday, October 2, 2019 - 1:14:17 AM
Last modification on : Thursday, October 3, 2019 - 1:22:05 AM

File

VERDET_CECILE_2019.pdf
Version validated by the jury (STAR)

Identifiers

  • HAL Id : tel-02303051, version 1

Collections

Citation

Cecile Verdet. Caractérisation multi-échelle du milieu karstique non saturé.. Mécanique des matériaux [physics.class-ph]. Université de Bordeaux, 2019. Français. ⟨NNT : 2019BORD0047⟩. ⟨tel-02303051⟩

Share

Metrics

Record views

71

Files downloads

8