The Lyon-Turin high-speed rail project includes a 57.5 km long twin-tube base tunnel. The design uses data collected from four exploratory tunnels, three in France, completed in 2010, and one in Italy, named “La Maddalena”. Excavation of this 7 km long Italian exploration tunnel was completed in February 2017 using a 6.3 m diameter main beam TBM under exceptionally high overburden of more than 2,000 m under the Ambin mountain slopes, where mild rockbursts were systematically experienced along nearly half of the alignment. The TBM excavated through gneiss and mica schists. Intercepted water inflows were lower than expected in the design phase, with temperature and chemical composition giving useful information. This exploration tunnel is the subject of the present paper.