The Ceneri Base Tunnel (CBT) in the canton of Ticino is the third longest railway tunnel in Switzerland. It is the continuation of the Gotthard Base Tunnel along a new transalpine railway line that has a total length of more than 70 km. The modern and flat route will allow speeds between 200 and 250 km/h. In contrast to the existing section, where additional locomotives are required to push the trains in order to cope with a slope of up to 26 ‰, the trains will no longer have to be pushed on the new section, which is also 40 km shorter than the existing section.
The 15.4 km long Ceneri Base Tunnel is being built as a double tube tunnel with a cover of 10 to 850 m. The parallel tubes are single track tubes separated by a space of 40 m. Every 325 m, the tubes are connected via crosscuts.
Intermediate heading near Sigirino
Via a 2.5 km long approach adit, an intermediate heading was driven near Sigirino from which the main tunnel is being simultaneously excavated at four different locations. The main section – Lot 852 – consists of two 8 km long drifts towards the North and of two approx. 6 km long drifts towards the South. The new tunnel is located in the crystalline rock of the Southern Alps in heterogeneous rock strata. Due to the fault zones that are expected in this area, tunnel advancement is primarily carried out using the conventional blasting method.
The project is divided into ten different excavation sections
In order to cope with the very different geological conditions, the project is divided into ten different excavation sections. The areas located in the most stable rock formations required flat inverts, few short rock bolts and a thin shotcrete lining. The sections where intermediate fault zones are prevalent were advanced using curved inverts, steel ribs in the crown, rock bolts in the tunnel walls and thick shotcrete lining. The areas located in the strongest fault zones were excavated using circular invert, steel ribs in the crown and invert, many long rock bolts and a thick shotcrete lining.
Rock bolts with a total length of 149,500 m
For all ten excavation sections, DYWIT Italy supplied R 32 and R 38 Ø rock bolts with a total length of approx. 149,500 m, all of which were flexibly adapted to on-site conditions. The self-drilling hollow bar system proved to be ideal in these difficult ground conditions because it can also be installed trouble-free and safely in a single step in unstable boreholes. In addition, DYWIT supplied a total of 93,000 Type EFB-160 and EFB-240 rock bolts. The expandable friction bolts achieve immediate full load bearing capacity over the entire installed bolt length and are therefore very suitable for advancing the Ceneri Base Tunnel in the prevailing fault zones.