Application of a Terrestrial Laser Scanner (TLS) to the Study of the Sechilienne Landslide (Isere, France)

The active Sechilienne landslide (Isere, France) has been continuously monitored by tacheometry, radar and extensometry devices for 25 years. Indeed, if the 3 mil. m(3) of rocks in the active zone named Ruines fell down, the debris would dam the Romanche valley. The breaking of the dam by overtopping and rapid erosion would bring a catastrophic flood and other dramatic consequences throughout the valley. Given the rockfall hazard in the most active zone, it is impossible to use targets in this area: Only reflectorless remote sensing techniques can provide information. A time-series of seven Terrestrial Laser Scanner (TLS) point clouds acquired between 2004 and 2007 enable us to monitor the 3D displacements of the whole scanned area, although point coverage is not homogeneous. From this sequential monitoring, the volume of registered collapses can be deduced and the landslide movement along the main geological structures can be inferred. From monitoring associated subsidence and toppling observed on TLS data, it can be deduced that blocks rearrangements are linked to structural settings and that the Sechilienne landslide is complex. To conclude, TLS point clouds enable an accurate monitoring of the evolution of the inaccessible Ruines area and, therefore, this device has proven its ability to provide reliable kinematic information, even in areas where on-site instrumentation is infeasible.