The Bodio section is the southernmost and, being 16 km in length, the longest of the five sections of the Gotthard Base Tunnel (57 km: the world’s longest tunnel). Most of the parallel twin tunnels have been mined using two open hard rock TBMs. During the drives through the Leventina Gneiss (massive gneiss alternating with highly fractured rock), the different ground conditions resulted in variable structural engineering effects. Furthermore, both TBMs unexpectedly met two fault zones of several hundred metres in length. These zones, due to both brittle and squeezing characteristics of the rock mass, were a particular challenge to man and machine and were successfully mastered thanks to appropriate technical solutions. This paper gives an overview of some of the technical experiences made during mining and lining works.