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The tunnel face during excavation: Eighty percent of the drive in the main tubes was cut by tunnel boring machines.

On June 1, 17 years after the first blast in the main shaft, heads of state and government of Germany, France, Italy, Austria, and Liechtenstein, as well as the European Commissioner for Transport, gathered for the first trips through the Gotthard Base Tunnel (GBT) during the opening festivities for the world’s longest railway tunnel. More than 2,000 individuals from the army, police, federal government, Swiss Federal Railways, AlpTransit Gotthard (ATG) and private companies provided security.

The Gotthard Base Tunnel consists of two 35-mile-long (57-kilometer-long), single-track tubes. With a rock overburden as great as 7,545 feet (2,300 meters), the Gotthard Base Tunnel is not only the world’s longest, but also the world’s deepest railway tunnel constructed to date. Including all cross-passages, access tunnels, and shafts, the total length of the tunnel system is more than 95 miles (152 kilometers). It links the north portal at Erstfeld, Switzerland, with the south portal at Bodio, Switzerland. Daily tunnel capacity is as many as 260 freight trains and 65 passenger trains.

For construction purposes, the Gotthard Base Tunnel was subdivided into five sections. Access adits provided access to the underground construction sites for personnel, materials, and machines. To save time and reduce costs, construction work proceeded on the various sections simultaneously.

Lined tunnel segment during construction.

For construction of the Sedrun section, access from the surface was provided through a 3,280-foot-long (1-kilometre-long) access tunnel and two 2,625-foot-deep (800-meter-deep) vertical shafts. From the foot of the shafts, the two tubes were blast-driven to the north and south. Because the deep overburden and high rock stresses threatened to deform the tunnel, special supporting means were necessary in some places. Engineers developed a new concept with flexible steel rings that partly closed under the rock pressure and thereby prevented deformations in the completed structure.

The first final breakthrough of the Gotthard Base Tunnel took place on Oct. 15, 2010, at 2.17 p.m. in the east tube, at a distance of about 18 miles (30 kilometers) from the south portal and 17 miles (27 kilometers) from the north portal. The breakthrough took place with great accuracy — a deviation of only 3 inches (8 centimeters) horizontally and 0.4 inch (1 centimeter) vertically.

Eighty percent of the drive in the main tubes was cut by tunnel boring machines; 20 percent by conventional drilling and blasting. A total of about 31 million tons of excavated rock was transported out of the tunnel.

Information provided by AlpTransit (alptransit.ch/en/home).

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