Istanbul is the only city in the world that is situated on two continents. The European part is separated by the Bosporus Strait from the Asian part. Most of Istanbul’s ten million population live in the European part. To supply the inhabitants of the European part with drinking water – as well as to meet the needs of industry and agriculture – it is intended to pump water from the Melen River dam in the Asian part of Turkey underneath the Bosporus into Europe. This will be done by driving the first ever mechanically excavated tunnel under the Bosporus. 

For the very first time a tunnel was to be produced by machine under the Bosporus. The route is extremely demanding, falling at a gradient of more than seven percent from the European bank to a depth of 135 meters below the surface of the Bosporus. 

April 13, 2009 marked a significant event in the world of tunnelling. With the breakthrough by the Herrenknecht EPB Shield S-391 (diameter 6.11 meters), a tunnel was driven for the first time connecting two continents. The 3.14-kilometer-long tunnel was completed safely and right as planned within 13.5 months and with best performances of up to 20 meters per day.

The tunnel is under the pressure of up to 13.5 bar. The lining segements were produced in moulds, that had been delivered to Turkey by Herrenknecht Formwork Technology. The segments produced in these moulds were designed to withstand up to 20 bar.