Severomuysky Tunnel

Severomuysky Tunnel (Russian: Северому́йский тонне́ль) is a railroad tunnel on the Baikal Amur Mainline (BAM), in northwestern Buryatia, Russia. It is named after the Severomuysky Range it cuts through. The tunnel is 15,343 metres (50,338 ft) long, the longest in Russia (excluding metro lines).

The tunnel cuts under the Severomuysky Range, a mountain ridge separating the Upper Angara basin to the north west from the Muya basin to the south east. The BAM then follows the valley of the Muyakan River on its way east towards its junction with the Muya shortly before Taksimo. A works town named after the tunnel was built at each end during its construction; Tonnelny at the western portal and Severomuysk at the eastern portal. Tonnelny was abandoned in 2004 after the opening of the tunnel and its population relocated to Severomuysk. Employment in Severomuysk relies almost entirely on the maintenance of the tunnel and its bypass route.

Preliminary work on the tunnel started in 1975, with tunneling commencing on May 28, 1977. The tunnel was built through very difficult rock with four major faults and a great deal of underground water, some at 35 atmospheres (3.5 MPa) pressure. One method used was to pump liquid nitrogen into the rock, freezing the water until the cut could be sealed. In September 1979 workers broke into a fault connected to a 12,000 cubic meter underground lake. This required building a drainage tunnel and delayed work for eighteen months.

When it became clear that the tunnel would not be completed in time for the planned official opening of the BAM in 1984, a 28 km bypass was built during the years 1982-83. This had a 4% grade and traffic was limited to 15 km/h. Passenger traffic was prohibited.

In 1989, a new bypass of 54 km was completed (with a 2% ruling grade) and the original bypass route was closed. The new route was open for passenger trains, although it required auxiliary engines to push trains up steep sections and was limited to a maximum speed of 20 km/h, the 54 km route taking around 2.5 hours to cross. This section featured a large number of tight curves and viaducts, with the long curved bridge built near the tunnel's western portal being nicknamed locally the Devil's Bridge. It also included 2 tunnels of its own, one of which was 2 km in length. It was also expensive to maintain and at risk of avalanches.

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