Gotthard Base Tunnel

The Gotthard Base Tunnel (French Tunnel de base du Saint-Gothard, Italian Galleria di base del San Gottardo, Rhaeto-Romanic Tunnel da basa dal Son Gottard) is the longest railway tunnel in the world at 57 km. It crosses the central Swiss Alps in a north-south direction and thus passes under the Gotthard massif, among others. The Gotthard Base Tunnel is a section of the Gotthard Railway and of the New Rail Link through the Alps (NRLA) transport concept covering the whole of Switzerland. The tunnel connects the German-speaking canton of Uri (north portal at Erstfeld, 460 m above sea level) with the Italian-speaking canton of Uri (north portal at Erstfeld, 460 m above sea level) at an altitude of 312 to 549 m above sea level (crest) and more directly than the older Gotthard railway (1882; crest tunnel under the Gotthard massif: 1151 m above sea level). ) with the Italian-speaking canton of Ticino (south portal at Bodio TI, 312 m a.s.l.) and consists of two 57 km long, parallel tunnels, which have the world's highest rock cover (approximately below Piz Vatgira) with the mountain strata above them rising to 2450 m.

At two points, it is possible for trains to change tracks between the two tubes, depending on the operating situation. In addition, there are 176 connecting galleries for pedestrians between the two tubes (cross-passages) at a distance of around 325 metres, which are used in the safety concept for evacuation from one tube to the other. The centre distance between the two tubes is normally 40 metres (max. 70 m). A total of 151.84 km of tunnels and galleries were thus bored and blasted into the mountain.

The mountain section of the Gotthard Railway, which went into operation in 1882, with its higher, 15 km-long summit tunnel, will remain in operation for the time being alongside the new line through the base tunnel. The connecting lines to and in Germany (especially on the upgraded and new Karlsruhe-Basel line) and Italy still need to be upgraded to take advantage of the increased capacity through the mountains.

The official opening ceremony - after 17 years of construction - was on 1 June 2016. Scheduled passenger services began on 11 December 2016 after several months of trial operation; freight services began as early as 5 September.

Purpose

In future, the journey time for passenger traffic with tilting trains between Zurich and Milan will be reduced by around one hour to approx. 2 h 40 min thanks to the Gotthard base tunnel, the Ceneri base tunnel and the access routes in Italy.

For freight traffic, this will enable environmentally compatible mobility using faster and heavier trains. This is demanded by the Alpine Initiative Association and in the federal popular initiative launched by it "to protect the Alpine region from transit traffic". The aim is to shift heavy goods traffic to the railways, as laid down in the constitution. Experts expect the transport volume to almost double in the foreseeable future to an estimated 40 million tonnes per year. In addition to the shortening of the line, the construction as a flat railway will contribute to this in particular, so that freight trains with a total weight of up to 4000 tonnes can travel at higher speeds on the new line. On the old Gotthard line, which is about 30 km longer and has a crest about 600 m higher (1151 m above sea level instead of 549 m above sea level), two locomotives can only pull trains weighing a maximum of 1400 tonnes.

The maximum weight for single four-axle locomotives through the base tunnel is up to 1700 t in the southbound direction and 1400 t in the opposite direction.

The new Gotthard Base Tunnel, together with the planned Zimmerberg Base Tunnel, forms the northern part of the Gotthard axis of the NRLA.

Location, course and geology

The Gotthard Base Tunnel connects Erstfeld on the Reuss valley floor in Uri with Bodio near Biasca in the canton of Ticino.

The tunnel lies along the route of the former Gotthard railway. The lengths given in km are to be put in relation to the old kilometry of the entire line, which has become shorter overall as a result.

The geological conditions were clarified by numerous test boreholes as well as temperature measurements and seismic surveys before construction began: different types of rock were found, from hard granite to yielding phyllites and schists of the Urseren-Garvera zone and the Tavetsch intermediate massif. Outside these problem zones, various types of gneiss predominate, such as Erstfeld gneiss or the strip gneiss of the Gotthard massif, and in the south in the Pennine gneiss zone mainly Leventina and Lucomagno gneisses. The test borings proved that a feared key geological point, the Piora syncline filled with sugar-grained dolomite, consists of dolomite marble at tunnel level without water pressure and flow. (Sugar-grained dolomite becomes completely cohesionless under the influence of water and pressure, i.e. in a sense liquid). When the zone was drilled through in the autumn of 2008, these concerns were finally laid to rest. Instead, kakirite, a soft, flowing rock flour, was encountered in other places, which led to extensive measures to secure and consolidate it.

The minimum curve radius in the tunnel is 5000 m. The north portal (upper edge of the rails) is at an altitude of 460 m above sea level. The south portal is at an altitude of 312 m. The apex of the tunnel is 549 m above sea level. The maximum overburden is 2450 m. The gradient rises from the north portal to the center by a total of 89 m with a maximum of 4.055 ‰, and from the south 237 m with a maximum of 6.76 ‰ are overcome. The projected maximum speed is 250 km/h.

The two tubes are longitudinally spaced 325 m apart and connected by 176 transverse tunnels. The distance, initially set at 650 m, was halved after the 1999 tunnel fire in the Mont Blanc Tunnel.

Cross section

The tunnel profile was derived from the EBV 4 clearance gauge of the SBB. For aerodynamic and climatic considerations, a free cross-sectional area in the tunnel of 41 m² was specified. The excavation diameter of about 9.20 m results in an inner diameter of about 7.76 m. The excavation is secured with 20 cm shotcrete (→New Austrian Tunneling Method), followed by an inner lining of in-situ concrete of at least 30 cm. The inner vault can reach thicknesses of up to 110 cm, and reinforcement is also installed in the event of high mountain pressure.