Analyse multi-méthodes de la déstabilisation d’un pylône de remontée mécanique implanté sur un glacier rocheux des Alpes françaises

• Published in: Géomorphologie : relief, processus, environnement
• Main Authors: Duvillard, Pierre-Allain, Ravanel, Ludovic, Schoeneich, Philippe, Marcer, Marco, Piard, Jean-François
• Format: Article in Journal/Newspaper
• Language: French
• Published: Groupe français de géomorphologie 2019
• Subjects: Remontées mécaniques; permafrost; glacier rocheux; subsidence; tomographie électrique résistive; Alpes françaises; Ropeway transport systems; rock glacier; Electrical Resitivity Tomography; French Alps; Pylon; Ice
• Online Access: http://journals.openedition.org/geomorphologie/12945

In the Val Thorens ski resort (Savoie, France), more than 79 infrastructure elements related to ropeway transport systems are located on permafrost. During the last decade, three of them (two top stations and a pylon located around 3,000 m a.s.l.) experienced destabilization which required important adjustment and stabilization work. This study investigates the destabilization of the pylon #2 of the Thorens funitel that occurred during the Summer 2016. Its foundations were affected by horizontal displacement and subsidence, causing a metric shift of the pylon top with respect to the cable. The pylon was built on a rock glacier which morphology was severely altered by earth work aiming to develop a ski slope. A multidisciplinary analysis was conducted in order to understand the processes that led to the pylon destabilization with a focus on the role of the morphological alterations of anthropogenic origin on the rock glacier dynamic. We used (i) a stratigraphic data analysis from boreholes and (ii) a subsurface analysis based on geophysics (Electrical Resistivity Tomography profiles) to understand the rock glacier internal structure, while (iii) geomorphological surface modifications were investigated by comparing digital terrain models obtained by aerial photogrammetry before and after the earthwork. This study highlights the preparatory role of the earthwork and a non-control of the surface water flow in an ice-rich environment such as a rock glacier. La station de Val Thorens (Savoie, France) concentre plus de 79 composantes de remontées mécaniques en contexte de permafrost probable. Au cours de la dernière décennie, trois d’entre elles (deux gares amont et un pylône), situées vers 3 000 m d’altitude, ont subi des déstabilisations partielles nécessitant d’importants travaux de confortement et de stabilisation. Cet article documente la déstabilisation du pylône n° 2 du funitel de Thorens au cours de l'été 2016. Ses fondations ont été affectées par un déplacement horizontal et un affaissement à l’origine d’un ...