Sixty metres below the Bosphorus Strait, work is progressing at an unrelenting pace on Turkey’s most ambitious infrastructure project to date.

Dubbed the ‘project of the century’, once complete, the $2.5 billion undersea rail link will help realise the movement of 70,000 passengers per hour across the 1.387 km strait in under four minutes.

According to reports, test runs on the project – slated to open in 2011 – will begin in 2010.

The project achieved a new milestone recently with the placing of two sections of the immersed tube, under water. Each 135-m long section weighs 15,000 tonnes and is vacuum connected to other sections with 30-cm-thick gaskets. According to the work schedule, one section will be immersed under water every two months.

Once all sections are placed underwater, the tunnel will be part of a 76 km long project of rail upgrades and connect rail lines on both sides of Istanbul, dropping the commute time between Gebze on the European side of Turkey with Halkali on the Asian side to an hour and a half. In addition, it will offer citizens an alternative mode of transport, that is fast, reliable, environmentally friendly with low air and noise pollution. It will also seek to reduce traffic on Turkey’s roads.

The project will be integrated with the Aksaray-Airport light railway system, the Esenler-Bagcilar light railway system, the Eminonu-Zeytinburnu tramway in Sirkeci, the Bakirkoy-Avcilar-Beylikduzu railway system in Bakirkoy, the Kadikoy-Kartal metro in Kadikoy and the Uskudar-Umraniye tramway in Uskudar. It will also offer link-ups to the Sabiha Gokcen and Ataturk airports.

As part of the project, 36 stations on the Gebze-Haydarpasa and Sirkeci-Halkali lines will be upgraded and the number of railway lines will be increased to three. The Yenikapi, Sirkeci and Uskudar stations will be underground, while Kazlicesme will be aboveground.

The project will run to a total length of 13.5 km and at 60 m below the sea, it will also be the world’s deepest immersed tunnel.

The 8.6 m high and 15.3 m wide tunnel will accommodate two-way traffic. All of the materials used in the construction of the tube tunnel are being made in Tuzla and transferred to points between Uskudar and Sarayburnu for immersion and assemblage.

The agreement for the construction of the tunnel was signed in May 2004 by the General Directorate of Railways, Ports, and Airport Construction (DLH), Japanese contractor Taisei Corporation, Gama-Nurol and Eurasia Consultant Firm and receives major funding from the Japanese Bank for International Cooperation (JBIC).

Challenging job

Well renowned for numerous construction and infrastructure projects in various cities in Turkey, Nurol is playing an important role in this prestigious project. The company has achieved great success in major infrastructure projects, manufacturing industry and residential construction, thereby significantly contributing to Turkey’s economic development along with providing support to contribute to the strength of the Turkish defence industry with its specialised staff, technological capabilities, creative designs and production.

“Being constructed as a double-track metro tunnel of approximately 13.5 km, the Bosphorus tube tunnel crossing has a section of 1.8 km under the sea constructed by 'immersed tube tunnel technology'. Other tunnel sections are constructed as cut and cover tunnels and bored tunnels by New Austrian tunnelling technology. This project also includes four underground stations,” says Bora Aydinay, spokesperson from the tendering group of Nurol Construction and Trading Company.

“Especially, at the beginning of the sea sections special soil dredging and treatment works shall be executed, the weaker soil sections and muddy locations will be taken away, treated and placed by stronger soil material,” he adds.

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