The Marmaray Project

Combining the names of the Sea of Marmara and “ray” meaning rail in Turkish, the Marmaray Project is one of Turkey’s greatest engineering feats ever undertaken. With the first phase opened in October 2013, the Marmaray Project is one of the major transportation infrastructure accomplishments in the world at present. Bridging Europe and Asia, plans for the Marmaray project were first developed in 1860. The technology at the time did not permit the construction of a tunnel under the seabed and the original ideas that were suggested leaned towards a floating type of tunnel placed on pillars constructed on the seabed. Several ideas were discusses and modified over the decades as technology continued to evolve and accommodate more complex designs. Finally, a comprehensive feasibility study was carried out and reported in 1987 that showed a railway mass transit connection from west to east in Istanbul and under the Istanbul Strait was feasible and cost-effective. The feasibility studies were updated a few years later and in 1999 the Republic of Turkey and the Japanese Bank for International Cooperation (JBIC) signed a funding agreement.


Considered one of the world’s greatest engineering works, the Marmaray Project involves replacing two existing railway tracks on both sides of the Istanbul Strait with three tracks and connected to each other with bored tunnels and an immersed tube tunnel. The entire new railway system will be 76 kilometers long of which 13.4 kilometers is underground. The main features of this phenomenal transport system includes an immersed tube tunnel, bored tunnels, NATM tunnels, three new underground stations, 37 surface stations, 165 bridges, 63 culverts, yards, workshops, maintenance facilities, an operations control center, completely new electrical and mechanical systems and procurement of 440 modern rolling stock. It can carry up to 75,000 passengers per hour and around 1 million passengers per day. The tunnel crosses under the center of Istanbul and under the Bosporus Strait to connect Europe and Asia.

At 60 meters below sea level, the deepest immersed tunnel in the world was constructed using a shield tunneling method. Considerable amounts of water and solid were flowing into the excavation pit and engineers decided to use a temporary sealing technique of ground freezing to get the tunnel boring machine with a diameter of 7.93 meters safely to the target excavation pit. Liquid nitrogen was introduced in drill holes around the area of the tunnel boring machine. The diaphragm wall in the pit was dismantled and a steel structure filled with concrete was installed as the entrance way. After the frost body was thawed on the mantle, the tunnel boring machine was able to safely enter into the last meters of the pit. The technique was then again used to expand the entry and for the final sealing. This tube was accessed by bored tunnels from Kazlıçeşme on the European side and Ayrılıkçeşmesi on the Asian side of Istanbul. Additionally, engineers used fire-resistant concrete that was developed in Norway to enhance safety.

The immersed tube tunnel was outfitted with temporary bulkheads to allow them to float while the insides remain dry. The segments were then held in place with temporary supports until the foundation was completed, after which the trench is backfilled.

A total of 1.3 million cubic yards was dredged out of the Istanbul Strait and carried to a confined disposal site created specifically for the project.

Connecting the Anatolian and European Sides of Istanbul by rail in a seamless way, the principle of applying two different systems on the same railway line is the first in the world in terms of signaling systems.


The immersed tunnel was constructed in an area prone to earthquakes, only 16 kilometers away from a seismic fault system. A number of strong earthquakes have occurred in the Marmara Region since 1500. One of the challenges engineers faced was constructing a safe underground tunnel for commuters to use. They had to ensure the tunnel remains watertight, any damage can be repaired easily, loss of life in such an event is avoided and any repair work does not result in the disruption of the operation of the facility. During the construction of the tunnel, engineers discovered an archaeological goldmine that comprised of the remains of a Byzantine port which was an important find. While archeologists were excited with this discovery, it forced engineers to hold off the project for a few years, prolonging the project schedule and increasing costs. Engineers also had to factor the fish migration through the Istanbul Strait. Turbid waters during this period were a major concern but fortunately, the waters remained constant and present through the entire period. Noise impact by the dredgers was also factored in as a hurdle that would keep the fish away during the migrations. Feedback monitoring was conducted during the entire construction process to counter this. Additionally, the marine works were carried out in a water channel through which more than 50,000 ships pass every year and across which a vast number of ferries and passenger boats travel backwards and forwards. Engineers dealt with various stakeholders from the Japan Bank for International Cooperation (JBIC), the European Investment Bank (EIB) and the Counsel of European Development Bank (CEB). The workers in the project came from various different racial, cultural and religious backgrounds which required engineers to have excellent interpersonal and communication skills to succeed.

Impact of the Project

Not only is the project expected to alter the daily traffic patterns of commuters, it is also expected to influence the development of the city and the region. Rail transportation in the region is expected to rise from 3.6% to 27.7%.

After the discovery of archeological findings, Istanbul is nominated as the European Capital of Culture for the year 2010. Additionally, UNESCO declared Istanbul a World Cultural Heritage site. Throughout the construction process, delegates from UNESCO would visit the site regularly to advise on the impact of the Marmaray Project on the cultural heritage of Istanbul and also monitor the implementation of the project.

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