The Furka Base Tunnel is a Swiss railway base tunnel on the Matterhorn Gotthard Bahn's Furka–Oberalp line, an east–west railway connecting the cantons of Valais and Uri. Its west portal lies east of Oberwald (VS), at above sea level and its east portal lies south of Realp (UR), at .
Prior to its construction, all traffic had to use the historic high-level route via the long Furka Summit Tunnel, which was only available seasonally due to the threat posed by heavy snowfalls. Construction commenced during 1971, taking ten years to complete. An innovative permanent support system was used, comprising rock anchors and a shotcrete coating, which included the first use of polyurethane-based grouting within a railway tunnel. The tunnel has a relatively narrow cross section, which has been attributed with slowing the construction effort somewhat. The interconnecting Bedretto tunnel was used during the Furka Base Tunnel's construction for the removal of excavating spoil as well as to moving supplies inwards; it has since been reused for ventilation.
The Furka Base Tunnel is in length, and replaced the previous track that climbed to an apex of above sea level, thus allowing year-round through service on the Furka–Oberalp line. In the middle of the base tunnel, is a access tunnel to Bedretto in the canton of Ticino (elevation ); some proponents of the project hoped to eventually build a Y-shaped tunnel connecting all three locations. The Furka Base Tunnel is completed by a bypass tunnel around Oberwald.
History
Background
Prior to the opening of the Furka Base Tunnel, all railway traffic on the Furka–Oberalp line traversed the challenging terrain between Valais and Uri via the historic high-level route using the long Furka Summit Tunnel.
The replacement of the Furka Summit Tunnel with a base tunnel had long been identified as an attractive solution, but the prospects for constructing such a tunnel were complicated by multiple factors in both its design and construction. Initial authorisation from the Federal Council for preparatory work was given in 1971.
The construction techniques used for the Furka Base Tunnel were relatively innovative for the era. One such technique involved the application of a recently developed polyurethane-based grouting to make the rock surrounding the tunnel portals impermeable. It was reportedly the first use of such material within a railway tunnel.
The completed Furka Base Tunnel accommodates a single track throughout, its cross section varying between 26 and 42 m<sup>2</sup> throughout its length.
During August 2018, a comprehensive modernisation of the Furka Base Tunnel's infrastructure commenced. This programme, costed at CHF 190 million, largely revolves around the refurbishment of the tunnel's structure, the wholesale replacement of the track and trackbed, as well as the incorporation of various safety measures. The tunnel is typically kept operational throughout the process by performing the majority of the work at night. Particular attention has been paid to the tunnel ventilation, intended to control threats such as fires. However, the study of several operational scenarios points out the weaknesses of the existing ventilation system and difficulties to dissipate the smokes without modifying the ventilation system.