The work deals with the evaluation of the stability conditions of several steep slopes hanging along a motorway track in the far east. The slope rock mass structure determines the possible unstable blocks that can induce rock fall phenomena. Consequently the stability analysis must be based on an accurate geo structural survey performed by using laser scanner to obtain a precise 3D digital model (DSM) of the rock surface. Discontinuity orientations and positions on the rock face are derived from the DSM in order to perform the reconstruction of the rock mass and to identify blocks lying on the slope. Stability analyses are determined by evaluating the kinematically feasibility of different failure mechanisms. The rock block shapes and volumes are computed by performing 2D and 3D analyses whereas the failure mechanisms are examined by Key Blocks methods.
In mountainous regions transportation corridors are often susceptible to landslides and, in particular, rock falls constitute a major hazard in numerous rock cuts. This is the case illustrated in this work, that regards a highway segment, about 5 km in length, excavated through 8 slopes and affected by several rock falls that determine a possible risk for highway users. The aim of the study was to establish the prevailing rock mass characterisation on the 8 slopes for the evaluation of instability phenomena based on traditional geostructural survey coupled with the LIDAR technology, in order to assess a relative hazard for the slopes, thus providing recommendations for remedial works. LIDAR application has enabled the acquisition of a very large number of measurement points in a short space of time. This measurement methodology has permitted the realisation of a 3D model of the rock slope (Digital Surface Model DSM). This model composed by a "cloud" of points is related to an image of the rock slope and it allows, through a specific software, the reconstruction of slope topography and the identification of the discontinuities in terms of position on the slope and orientation, spacing, persistence and joint hierarchy. Data acquired with the two different approaches (compass and LIDAR) have been merged together in a consistent data sample of the discontinuity and statistically treated. This has led to recognize typical discontinuities for each slope describing them from a geomechanical point of view. Once determined both the topography of the slope and the geo structure, stability analyses have been performed using the Key Block method. The different possible kinematics modes have been determined and the possible unstable blocks factor of safety and volumes calculated. On this base remedial work typologies have been suggested.
From a geological point of view the slopes are composed of porphyritic biotite granite belonging to Kledang Range of Triassic Age. Quartz veins, aplite dykes and pegmatites of variable orientation and size are also present within the granite bedrock.
