1734) Turkey Building the World's Deepest Immersed Tube Tunnel

Immersed tunnels are built in sections, floated to the site of assembly (A), then sunk to the seabed (B). More than 35 million cu. ft. of soil, sand and gravel will be dredged from the floor of the Bosporus for the project.

PopularMechanics.com June 2007. .

Since the 19th Century, Turks have dreamed of connecting Europe and Asia via a tunnel under the Bosporus. Soon, that dream will come true in the form of the 8.25-mile-long Marmaray Tunnel, which will provide a rail link for a rapid transit system.

Tunnels on such a scale have been built before, but the Marmaray engineers had to deal with an extra hurdle — they're working in an earthquake zone. According to seismic experts, the nearby North Anatolian Fault has a 62 percent chance of generating a strong quake within the next 30 years. The solution: While most of the tunnel will be bored through solid rock, the central mile-long section under the Bosporus will consist of an "immersed tube" fabricated in sections on the surface and then sunk and joined together on the seabed. Unlike a tunnel bored through rigid rock, the submersed sections will be connected by flexible joints made of thick, rubber-reinforced steel plates, which can absorb quake movement without breaking. When it opens in 2010, the Marmaray will be the deepest such tunnel ever constructed, with a maximum depth of 180 ft. And, East and West will meet without getting their feet wet.





MARMARAY TUNNEL
Location: Istanbul, Turkey
Price Tag: $3.3 billion
Completion Date: 2010
Total Length: 8.25 miles
Immersed Section: 4600 feet

SEIKAN TUNNEL
Claim to fame: Longest, deepest rail tunnel
Location: Japan
Date completed: 1988
Length: 33.5 miles
Maximum depth: 787 feet

CHANNEL TUNNEL "CHUNNEL"
Claim to fame: Second longest rail tunnel
Location: England to France
Date completed: 1994
Length: 31 miles
Maximum depth: 246 feet

LAERDAL TUNNEL
Claim to fame: Longest road tunnel
Location: Norway
Date completed: 2000
Length: 15.2 miles

By Jeff Wise
Illustration by Transluszent