Special Features

Special Features
Special Features

1 Roman era Valens Aqueduct
2 Hagia Sofi a Mosque, the greatest masterpiece of Byzantine architecture
3 View of Istanbul city

Chronic Traffic Congestion and Worsening Air Pollution

The Republic of Turkey is close to economic regions such as Europe, Asia, Middle East, etc. Its presence as an international economic hub is increasing, it has enjoyed significant economic growth in recent years, and now has a population of 75 million.

Chronic Traffic Congestion and Worsening Air Pollution

The Bosporus Strait, which passes through the center of Istanbul, the largest economic center in Turkey, divides the city into an Asian side and a European side. For a long time the Bosphorus Strait has been a barrier to traffic. In fact, the idea for an undersea tunnel crossing the Strait has existed since the time of the Ottoman Empire. At present two suspension bridges have been constructed across the Bosporus Strait, but because of chronic traffic congestion and worsening atmospheric pollution associated with this congestion, securing a new traffic route has become an urgent task, so the opening of a high-capacity railway that is capable of reducing the environmental burden is urgently required.

New Traffic Route to Improve the Congestion

Therefore the concept was born to construct an underground railway tunnel crossing the Strait. The scheme would improve not only the congestion and the environment, but also the historic landscape. Also as a measure against earthquakes, Taisei aimed for a "100 year tunnel" that would withstand a gigantic earthquake. As a result of the company's vast experience in tunnel construction, we submitted technical proposal with advanced technology, and in August 2004 the latest technologies were invested and the challenge of this difficult project that spans the centuries commenced.

New Traffic Route to Improve the Congestion

Conserving the Culture and Environment of Istanbul

Istanbul is an ancient city that flourished as a capital city of three great empires: the Roman, Byzantine, and Ottoman Empires, and is a treasury of historical assets. Actually, during the construction of underground stations on this project, groups of remains from these three eras were discovered. The construction period of the project was extended due to extensive archeological surveys, but we cooperated in these archeological surveys to conserve these important cultural assets of Turkey.

Conserving the Culture and Environment of Istanbul

Realization of a 150 year-old Dream for Turkish People

In February 2011, the connection between the land tunnel sections and the immersed subsea tunnel that connects Europe and Asia was completed. Prime Minister Erdogan proudly proclaimed the realization of the 150-year-old dream dating from the 1860s. In the autumn of 2013 operation of the railway is planned to start.

Realization of a 150 year-old Dream for Turkish People

Taisei's Technology meeting the World's Challenges

The underground railway line of the Bosphorus Strait railway tunnel construction mega-project is a joint project extending over a total of 13.6 km, and includes approximately 1.4 km of immersed tunnel across the Strait, about 9.5 km of shield tunnel (two lines of inbound and outbound track) connecting to the immersed tunnel, three underground stations, and one above ground station.

The Challenge of Constructing an Immersed Tunnel under the Strait in Great Water Depth and Rapid Tidal Flows

The major feature of the project is the subsea tunnel crossing the Strait. For this, the immersed tunnel method was adopted, in which large precast concrete tunnel elements are sunk to the seabed and connected.
It is known that the Bosphorus Strait has tidal flows that have different direction in their upper and lower layers. Under these severe natural conditions, monitoring of the weather and sea conditions was carried out over one year, and a system for predicting the daily flow speeds was developed, so that precise construction could be carried out safely. As a result of repeated investigations and tests carried out by the Taisei Technology Center, the world's deepest immersed tunnel was completed.

Massive Immersed tunnel elements with service life of 100 Years

The massive immersed tunnel elements with a maximum length of 135 m, height 8.6 m, and width 15.3 m require the highest standard of design and construction in order to maintain water tightness while withstanding up to 60 m depth of water pressure.
Also, the tunnel elements consist of, a reinforced concrete box structure encased on the outside by a waterproof steel plate, to provide water tightness and durability for the tunnel to last 100 years.

Massive Immersed tunnel elements with service life of 100 Years

The World's First RC Immersed Tunnel Elements Constructed on the Sea

The bottom half of the immersed tunnel elements were first constructed on dry land, and later the top half was constructed off shore. One by one, the tunnel elements were towed by ship from a location 40 km away from the tunnel to their installation location, where they were sunk.

The World's First RC Immersed Tunnel Elements Constructed on the Sea

Highly Accurate Tidal Flow Prediction System

The "tidal flow prediction system" which we developed is an online prediction system to predict complex flow conditions. The weather, water levels, and flow velocities were measured in real time near the construction site, and the prediction of the tidal flows for a continuous 36 hours for the scheduled immersion day was produced by an analysis computer. The work was carried out after determining whether it was safe to carry out the immersion. * See the image 1 

The World's First RC Immersed Tunnel Elements Constructed on the Sea

Work vessel immersing tunnel elements

Directly Connecting Different Types of Tunnel

The challenge of directly connecting to the immersed tunnel under the sea was a world's first.
First, a shield machine excavated from the land side to the connection area under the strait close to the shore. This connection area is an artificial underground embankment between the under sea tunnel and the land side. The allowable tolerance was about 10 cm. After the shield machine had arrived at the immersed tunnel under high accuracy control, special waterproofing technology was used. In February 2011 the 13.6 km of railway tunnel connecting Asia and Europe was opened. * See the image 2  

Directly Connecting Different Types of Tunnel

Schematic diagram of the connection between the shield tunnel and the immersed tunnel

Tunnel Construction under the City

The shield construction method was adopted for constructing the tunnel under land. The shield tunnel, which comprises 70% of the route, passes under densely built residential areas over virtually its whole length, but it was possible to complete the excavation without affecting any building. Sirkeci Station was constructed below a very high density residential area. The structure of the station was complex at this location, so the NATM construction method was adopted. In order to minimize demolition of historical buildings, the station was constructed underground using only two vertical shafts.

Tunnel Construction under the City
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