ABSTRACT
A detailed structural analysis has been carried out based on the field observation and on a High Resolution Digital Elevation Model (HRDEM) derived from a terrestrial and airborne (provided by Swissphoto) laser scanning point cloud. The software COLTOP3D (Jaboyedoff et al. 2007) has been used to determine the orientation of the different discontinuity sets and the result is a colorful point cloud where each color is assigned to a spatial orientation (Fig. 3). When all the discontinuity sets have been identified, the potential failure mechanisms and the kinematic have been tested. (Hoek & Bray, 1981). The potentially unstable volumes have been calculated using two methods: the Sloping Local Base Level (SLBL) method and by a geometrical analysis on the airborne laser scanning point clouds. The SLBL method applied to a 3D surface consists of replacing the altitude zij of a DEM node by the mean value of the highest and the lowest node altitude among the four direct neighbors, only when the altitude zij is greater than the mean value (Jaboyedoff et al. 2009). The geometrical method using Polyworks (InnovMetric, 2009) consists in fitting plans along the main discontinuity sets in order to calculate the maximum volumes that could be
mobilized. Finally, the limit equilibrium analysis code SWEDGE® was used for a preliminary safety factor (SF) calculation when the instabilities are structurally controlled. When the discontinuity sets are difficult to detect and when the failure mechanism takes place on the intact rock mass following a pseudo circular failure surface, the software SLIDE® was used. Both methods are based on a limit equilibrium analysis assuming a static situation.
