“La Maddalena” exploratory adit - base tunnel of the Turin-Lyon high speed rail project: hydrogeological monitoring data analysis

“La Maddalena” exploratory tunnel, located in Chiomonte (Italy Western Alps - Susa Valley), is one of the four exploratory adits, three in France, completed in 2010, and one in Italy, whose realization is related to Turin-Lyon high-speed rail project. The excavation involve the ‘‘Pennidic Domain’’, and more in details the tectonic contact between Piemontese Zone and Brianzonese. During the tunnel construction several monitoring data have been recorded in order to assess geological parameters important for the future Base Tunnel realization. In fact, one of the main task in the optimization of the final design of a Tunnel has been represented by the hydrogeological monitoring. This activity has been aimed to verify the correctness of the project hypothesis and especially to evaluate the inflow forecast in term of discharge rate and distribution, temperature and chemical facies of groundwater. The hydrogeological monitoring has proved extremely valuable not only in checking the reliability of the tunnel design forecast but also in underlining the importance of the realization of exploratory tunnels prior to the excavation of a main tunnel.