The project aims to address the critical issues on the section of road 251, characterized by high tortuosity of the route, poor visibility, narrow roadway, lack of stopping places, and exposure to hydrogeological and avalanche risks. To this end, the construction of a tunnel consisting of a single two-way lane with a total length of about 755 m (of which 30 m artificial and 725 m natural) is planned. The geological-geomechanical study made use of detailed field surveys, the execution of two seismic profiles (MASW, HVSR, and refraction seismics), and four drillings with laboratory tests on the extracted samples to define the geomechanical parameters. Based on the conducted investigations, it was then possible to perform a 2D finite element modeling in a plane strain state, through a continuous model of the rock mass. In the development of the project, particular attention was given to the mountainous context in which the structure is located, finding solutions that were compatible from a landscape and environmental perspective: the two entrances are indeed characterized by significant reshaping of the rock walls, followed by covering and concealing of the walls through the construction of reinforced earth structures up to about 20 m high. For the stability analyses of the excavation fronts at the entrances, it was also possible to take advantage of consultancy from the University of Perugia.
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