Analysis of the behaviour of a carbonate rock mass due to tunneling in a karst setting.

Sorrento Peninsula is one of the most famous touristic resort of southern Italy. The high energy relief of the carbonate mountains, reaching over 1,100 m above sea level at a very short distance from the coastlines, along with the widespread development of karst processes, make the area extremely complex as regards the constructionof infrastructure lines. In the past, construction of railway and road tunnels was affected by serious problems due to instability phenomena, in part related to karst processes. In particular, the sector of Vico Equense is characterized by several collapse sinkholes, together with a number of further karst landforms. In this paper we describe the activities performed during the construction of a tunnel for water disposal. The tunnel, entirely realized in carbonate rock masses, is some hundreds of meters long and shows at several locations karst natural caves, the main one of which was surveyed by means of laser scanner techniques. Such an approach made possible the remote sensing collection of discontinuity strikes and dips even along the chimney-like vertical caves. These data, combined with those derived from the classical geomechanical survey within the tunnel, allowed to characterize the rock mass and to evaluate the stability conditions in the different phases of the tunnel advancement. In the present paper, the geostructural and the geomechanical characterization of the rock mass are discussed, along with the analysis of the rock mass response to tunneling carried out by means of the discrete element method.