Marmaray Tunnel

A few days ago, on October 29th, 2013, a new railroad tunnel opened in Turkey, called the Marmaray Tunnel. Normally, we do not talk much about current rail industry events, and even more rare is mention of foreign rail industry news, however the Marmaray Tunnel is globally significant for several reasons. Most significant perhaps is the fact that the Marmaray Tunnel is the first intercontinental railroad tunnel, linking Europe with Asia.

The Marmaray Tunnel is an underwater tunnel just north of the Sea of Marmara. It crosses under the Bosphorus Strait and connects two parts of Istanbul, Turkey. At nearly 200 feet below the surface of the sea, it is the world's deepest immersed tube type tunnel. It is about 8.5 miles long and consists of two single track tunnels. The railroad line is standard gauge and is electrified using an overhead catenary.

The tunnel had some engineering challenges, due partly to the length and the location. Being underwater, there was some concern that if a tunnel wall sprung a leak, it could potentially flood the entire tunnel and cripple the rail system. In order to minimize this risk, each section of the tunnel was built from waterproof concrete, which is coated with a steel shell. Each section of the tunnel is independently watertight, and there are floodgates between sections which can be closed to isolate any leakage to just a single section. This is all important because the tunnel is located within 11 miles of the North Anatolian Fault, and geologists have estimated that the chance of an earthquake of a magnitude in excess of 7.0 in the next 30 years is over 75 percent. Additionally, the soil on which the tunnel is resting has been known to liquefy during major earthquakes, so industrial concrete was pumped into the soil to a depth of about 80 feet to help stabilize the foundation for the tunnel.

Currently the tunnel is only handling passenger trains serving Istanbul. Tunnel administrators are entertaining the possibility of using the tunnel for freight traffic, though no official plans to do so have been published at this time. If freight traffic were allowed to use the tunnel, it would be conceivable for freight to move by rail from Beijing to London.

Marmaray Tunnel is part of a larger project which involves building regional commuter rail lines around Istanbul, and improving existing commuter rail and subway lines, and building new rolling stock for these rail lines. When the project is complete, the entire rail line will be about 47 miles long and include 37 surface stations and three underground stations. When the project is complete, trains will be able to run as frequently as every two minutes. The section of the line that opened on October 29 includes just four stations, and the rest of the line is expected to be operating by 2015.

The tunnel was originally started in 2004, and was planned to be completed in 2009. The completion of the tunnel was delayed four years primarily by numerous archaeological discoveries made within the areas being excavated. These archaeological finds had to be carefully preserved and removed before the project was allowed to continue. Some artifacts dated back over 8,000 years, and there were discoveries made from almost every era of the area's history.