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 alternate mode of transport, that is fast, reliable, environmental friendly with low air and noise pollution and also seek to remove the traffic off 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.
Compressed air supplied by Atlas Copco compressors (see separate report) is a key component in the current work of specialist contractor Bauer for the diaphragm wall construction and sub soil jet grouting of a new 13 km underground metro station of the Yedikule-Kadiköy rail system which forms part of Istanbul’s Marmaray project. When completed, the north and south diaphragm walls will be 280 m long and the west and east sides will each be 35 m. Additional work is also being carried out by Bauer which will improve the subsoil below the foundation level of the underground station with a water-cement mix injected at high pressure through a small bore hole.
“While the first stage of the 13.7 km Bosphorus Rail Tunnel project comprised of tunnel parts sunk into the depths of the sea, which would ultimately connect with railways both in Europe and Asia, the second stage of the Marmaray Project involves surface metro work.
Commenting on the concerns, he adds: “We were particularly worried about the safety of the project and have carried out seismic earthquake analyses in the early stages of the project. The project is built to resist tremors of the magnitude of up to 9 on the Richter scale,” says Binali Yildirim, Turkey’s transport minister.
There was a strong desire to construct a railway mass transit connection from west to east in Istanbul and under the Bosphorus Strait in the early 1980s, and consequently the first comprehensive feasibility study was carried out and reported in 1987, which concluded that such a connection would be feasible and cost-effective in the long run. The project as outlined in 1987 was discussed during the following years, and around 1995 it was decided to make more detailed studies and update the feasibility studies, including the passenger demand forecast from 1987. These studies were concluded in 1998, and the conclusions underlined the earlier conclusions that the project would offer many advantages to the people working and living in Istanbul, and it would ease the rapidly growing problems regarding traffic congestion in the city.
Work on the Marmaray metro project started in 1992 and a short line was operational by 2000, which although just 7 km long is currently transporting as many as 70,000 passengers per hour, indicating the urgent need for the extension of the project. The entire upgraded and new railway system will be approximately 76 km long with main structures and systems including the immersed tube tunnel, bored tunnels, cut-and-cover tunnels, at-grade structures, three new underground stations, 37 surface stations (renovation and upgrading), operations control centre, yards, workshops, maintenance facilities. In addition upgrading of existing tracks includes a new third track on ground, along with completely new electrical and mechanical systems and procurement of modern railway vehicles.
Previous studies on the project had included seismic and mechanical drillings with compaction-grouting works planned in an area of 461 m by 19 m on immersed tube tunnel line. A specially equipped sea-platform will have 3200 drillings up to 25 m on the seabed. Special equipments will pump cement in those bore holes and improve replacement ratio of soil where immersed tube tunnel members will be located. In this part of the project, there will be no dredging on the seabed. The special equipment and construction methods will prevent any direct cement spillage. No chemical additives that may harm the environment will be used as well, the spokesman concludes.