Near Grenoble (French Alps), a 100 million cubic meters slope movement threatens the Romanche valley and has been monitored since 1985. The deformation mechanisms are very difficult to identity. A simplified geomechanical model of the rock mass has been used to simulate the excavation of the valley, with finite and distinct element methods. The results obtained allow to explain some morphological features of the slope and are compatible with the present movements.
Pres de Grenoble (Alpes françaises), un mouvement de versant de 100 millions de mètres cube, qui menace la vallee de la Romanche, est ausculte depuis 1985. Les mecanismes de deformation sont très difficiles a identifier. Un modèle geomecanique simplifie du massif rocheux a ete utilise pour simuler I'excavation de la vallee, par les methodes des elements finis et des elements distincts. Les resultats obtenus fournissent une explication de certains traits morphologiques du versant et sont compatibles avec les mouvements actuels.
Nahe Grenoble (französische Alpen) befindet sich ein seit 1985 unter Beobachtung stehendes Hangrutschungsgebiet mit einem Volumen von 100 Millionen Kubikmetern, welches das Tal der Romanche bedroht. Die Verformungsmechanismen sind sehr schwer identifizierbar. Ein vereinfachtes geomechanisches Modell der Felsböschung mit finiten und distinkten Elementen wurde zur Simulation der Talentstehung genutzt. Die erhaltenen Ergebnisse erklaren einige morphologische Besonderheiten dieser Felsböschung und entsprechen den momentan stattfindenden Bewegungen.
Deformation mechanisms of some large slope movements in mountain areas are very difficult to identity. To be understood, they need to be considered as the result of a long term geological process, and then to be analyzed in the appropriate space-time scale. This is the case for the Sechilienne slope movement, which will be described later. The geomechanical models presented in this paper have been elaborated to highlight the evolution of the rock mass, due to the formation of the valley, and to analyze the influence of different factors on its present behaviour. The models are not aimed at predicting the future behavior of the slope. We think that, for movements which are as complex as the Sechilienne landslide, geomechanical simulations are not sufficient for this purpose, and must be used together with more empirical approaches.
The Sechilienne slope movement takes place on the north flank of the Romanche valley, 20 km upstream from Grenoble (Figure 1). Rockfalls at the front of the unstable mass were well known by the former generations of inhabitants who called the site "Les Ruines" Their reactivation in 1985 proved dangerous for a major highway (RN 91) and led to a complete geological survey of the slope and to the installation of a large monitoring net to measure displacements, by geodesy and extensometry. These studies showed that the movement extends up to the crest and, consequently, that the unstable mass is much larger than the 3 million cubic meters of the very active frontal zone. First volume estimation of the unstable mass was 50 million cubic meters but recent geodesic and underground observations lead to an estimation of about 100 million cubic meters. Different rockfall scenarios have been studied to estimate and prevent the damages wind effect, damming of the valley, flooding …
