Abstract
Switzerland's national government and parliament have approved construction of two new railway axes through the Alps. This is the 'New Alpine Transversal (NEAT)' scheme with the Gotthard and Loetschberg axes. The project will provide a vital link between the high speed rail networks of Germany and Italy, and produce a much-needed reduction in the heavy road traffic over the Alps by switching it to the rails. The longest NEAT tunnel, the Gotthard Base Tunnel (GBT), is about 57 km long. The tunnel consists of two parallel single-track tubes, which are connected by crosscuts at about 300 m intervals. The exceptional length of the GBT requires that special consideration be given to achieving both efficient construction and adequate ventilation under traffic. In order to achieve an acceptable over-all construction time, intermediate points of attack were conceived. Besides providing additional points for concurrent tunnel heading, they will serve as ventilation inlets and outlets once the tunnel is under traffic. The three intermediate points of attack have been topographically arranged to divide the tunnel into sections of roughly equal length and to geologically difficult sections to be tackled at an earlier stage of the tunnel project. The Sedrun and Faido sections each include a multifunctional station (MFS). In the event of an accident they provide safe rooms for passengers. Fresh air will reach them via the access galleries. Smoke can be extracted the same way, separated from the fresh air. In the MFS's special emergency train stops are linked by a gallery system to enable passengers to transfer from one tube to the other. Trains will be able to switch from one tube to the other by using a tunnel crossroad. It will also to be possible to close individual sections of the tunnel tube between the portal and the emergency stop or between the emergency stops themselves for maintenance. The maintenance schedule and the high demands to be met by the rail technical equipment are designed to reduce disturbances to a minimum. At the Gotthard axis, not only the Base Tunnel, but the entire axis had to be planned and designed to enable high-speed passenger trains to travel at speeds of 200-250 km/h, and freight trains to travel at 140 km/h. As a result the tunnel portals must be built at an elevation of 600-800 m lower than those of the existing Gotthard Railway Tunnel. This leads to a maximum overburden of up to 2300 m, one of the geotechnical challenges of this tunnel. Nearly 90% of the entire drive can be headed by using tunnel boring machines. The remaining part of the section in Sedrun will be excavated by conventional means, due to unfavorable geotechnical conditions in this section. In 1996 the construction began at the Sedrun intermediate access-gallery. Since 2001 the four main lots of the tunnel tubes are under construction. The paper deals with the latest stage reached as well as what the future will bring. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.
Published Version
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