Landslides in the coal-bearing series of the Arc Valley, France

The right bank of the Arc Valley bears a number of huge landslides located between Saint-Michel-de-Maurienne and Modane. They mainly affect the coal-bearing series of the “Briançonnais facies belt” which is famous throughout the Western Alps for being prone to slope movements of many types and sizes. aper describes the three major slides: the Poucet, Francoz and Bonvillard slides. Two of these slides extend from the very crest down to the valley bottom, with elevation differences ranging between 1400 and 1700 m. slides have long been identified because of their geomorphological expression. However, they have never been studied in detail owing to their size and a lack of practical interest. Indeed their displacement has been sufficiently slow to result in only minor damage to the railway and road in the area. ly, preliminary studies for a deep tunnel on a section of a new motorway (construction of which has just started) required that significant subsurface investigations be carried out. sical surveys and associated exploratory borings have provided a great deal of information on the thickness of the landslides and shows them to be essentially of the planar type.