Engineering - geological problems in the execution of an urban tunnel with small covering in pyroclastic formations underneath an old town center

This work treates the engineering-geological problems, the criteria followed to design and the technologies used in the execution of an urban tunnel with small covering in pyroclastic formations underneath the old town city of Zagarolo (Rome). The geognostic surveys showed that the excavation affected only pyroclastic formations, present in outcrop on a wide area of Southern and Centrai Italy, whose morfology has always favoured urban settlement. On the other hand, the increasing of road and railway traffic in the present and in a recent past have produced an adjustment and improvement of the road and railway facilities requiring underground excavations affecting also this kind of formations. Often these tunnels have been realized with small covering causing the highest interaction with the existing overlooking structures. These execution problems, typical of underground works in urban environment, reach particularly difficult levels when the overlooking structures have an historicalartistic interest.