Geostructural and Geomechanical Characterization of Rock Exposures for an Endangered Alpine Road (Italy)

The paper summarizes the main results of a study aimed at qualifying the geostructural-geomechanical rock mass conditions that affect rock slope stability along the upper tract (Italian-Swiss border) of the endangered "Val Vigezzo" Alpine national road and singles out the road sectors that show potentially unstable behaviour. The road was subdivided into 18 sectors and the study was developed according to: in situ exploration; rock laboratory testing; characterization through rock mass classification systems, and evaluation of the potential instability modes. The judgment derived on the stability conditions of the rock slopes is rather pessimistic, that is: of the 18 road sectors, 12 are described as unstable with 5 sectors ranked as fully unstable. The block theory and toppling analyses confirm a high potential for rock slope instabilities. For the stabilization measures to be effective, systematic anchoring of the rock exposures, anchored concrete walls, or reexcavation are required on a very difficult terrain. The excavation of diversion tunnels in the fully unstable sectors therefore seems to be the only way of obtaining permanent remediation. This qualification technique could be applied for preliminary evaluation of rock slopes instability over a large area.