Marmaray

Construction started in 2004 and was originally intended to be completed by April 2009.[3] After multiple delays caused – among other things – by the discovery of historical and archaeological sites along the route as new stations were built, the first phase of the project was finally opened by prime minister Erdoğan on October 29, 2013.[4][5] The second phase of the project was scheduled to open in 2015 but work once again stopped in 2014.[6][7] It was restarted in February 2017 and the line finally opened in its entirety on March 12, 2019.[8] The trains came with completely new rolling stock, with carriages that can be walked through from end to end.

The line can carry 75,000 passengers per hour in each direction (PPHPD).[3][9] Travel time from Halkali to Gebze normally takes 104 minutes.

The Marmaray is integrated with other parts of the Istanbul public transport network, including the Metro and the Metrobus network, via a number of interchanges. It is also integrated with the YHT high-speed train network to Ankara, Eskişehir and Konya, as well as with the international trains to Sofia in Bulgaria which depart from Halkalı.

The project involved building a 13.6-kilometre (8.5 mi) tunnel under the Bosphorus and upgrading 63 kilometres (39.1 mi) of existing suburban railway lines to create a 76.6-kilometre (47.6 mi) high-capacity passenger line between Halkalı and Gebze, along with the provision of 440 electric multiple unit carriages.

First phase

The contract for the project was awarded to a Japanese-Turkish consortium led by Taisei Corporation in July 2004.[4] The consortium included Gama Endustri Tesisleri Imalat ve Montaj and Nurol Construction.[10]

The Bosphorus (Istanbul Strait) is crossed by a 1.4-kilometre-long (0.87 mi) earthquake-proofed immersed tube, assembled from 11 sections – eight are 135 metres (443 ft) long, two are 98.5 metres (323 ft), and one element is 110 metres (360 ft).[11] Each section weighs up to 18,000 tons.[12] The tube was placed 60 metres (197 ft) below sea level, beneath 55 metres (180 ft) of water and 4.6 metres (15 ft 1 in) of earth.[12] It is accessed via tunnels bored from Kazlıçeşme on the European side and Ayrılıkçeşmesi on the Asian side of Istanbul and represents the world's deepest undersea immersed tube tunnel. Fire-resistant concrete developed in Norway was essential for the safety of the project.[13]

Construction started in May 2004 and the Marmaray tunnel was completed on September 23, 2008,[14] with a formal ceremony to mark its completion on October 13.[15]

Path of the rail tunnel project (dotted line) within the Marmaray railway, across the Bosphorus strait

Second phase

The second phase of the project involved the renewal of the old suburban railway that ran between Halkalı and Kazlıçeşme on the European side of Istanbul and between Ayrılıkçeşmesi and Gebze on the Asian side. The work was meant to be completed at the same time as the first phase (the tunnel and underground sections), but was delayed until March, 2019.

A third line was added to enable the electric multiple unit (EMU) cars and other railway carriages to move separately.[7] Thirty-six above-ground stations along the line were rebuilt or completely refurbished.[16][17] Signalling was also modernised to allow trains to travel as close as two minutes apart (although in reality far fewer trains than that actually run).

The suburban-rail upgrade part of the project, known originally as CR1, was first awarded to the AMD Rail Consortium, comprising Marubeni of Japan, Dogus Insaat of Turkey and Alstom of France.[18] However, they were unable to complete the work and it was re-tendered as contract CR3 in early 2011. The replacement contract worth €932.8 million was awarded to a joint venture between OHL and Invensys Rail.[18]

A Marmaray train at Bostancı station on the first day of operation of the Gebze–Halkalı line

A Marmaray train at Kazlıçeşme

The Marmaray uses TCDD E32000 rolling stock manufactured by Hyundai Rotem in ten- and five-car EMU configurations. The original €580 million contract called for 440 vehicles to be produced locally by Eurotem, Hyundai Rotem's joint venture with Turkish rolling stock manufacturer TÜVASAŞ. Hyundai Rotem was chosen ahead of Alstom, CAF, and a consortium of Bombardier, Siemens, and Nurol.[23]

There are two depot and maintenance yards on the line (one at each end) where the sets are stocked.

The project was delayed by four years, largely due to the discovery of Byzantine-era and other 8,000-year-old archaeological finds on the proposed site of the European tunnel terminal at Yenikapı in 2005.[24] Excavations then produced evidence of the city's largest harbour, the 4th-century Harbour of Eleutherios (later known as the Harbour of Theodosius).[12] Archaeologists also uncovered traces of the city wall of Constantine the Great, and the remains of several ships, including what appears to be the only ancient or early medieval galley ever discovered, preventing the project from proceeding as planned.[25] In addition, archaeologists uncovered the oldest evidence of settlement in Istanbul, with artefacts, including amphorae, pottery fragments, shells, pieces of bone and horse skulls, and nine human skulls found in a bag, dating back to 6,000 BCE.[12] Glass artefacts and fragments dating from the Hellenistic, Roman, Byzantine and Ottoman periods were also found during excavations at Sirkeci.[26]

Marmaray train passing under the Bosphorus as depicted in tile in Sirkeci Station

On August 4, 2013, Prime Minister Recep Tayyip Erdoğan, test-drove the Marmaray from Ayrılıkçeşmesi station (originally İbrahimağa station)[27] on the Asian side under the Bosphorus and back again.[28]

On October 29, 2013, the first stage of the Marmaray project, the underground tunnel between Europe and Asia, was inaugurated on the 90th anniversary of the Turkish Republic'.[4] The maiden journey took place after a grand opening ceremony attended by President Abdullah Gül and Prime Minister Erdoğan, as well as by the Japanese Prime Minister Shinzō Abe, the Romanian Prime Minister Victor Ponta, the Somali President Hassan Sheikh Mohamud, and a number of foreign civil servants.[4]

On November 7, 2019, the first Chinese freight train to Europe ran through the tunnel. This demonstrated that the China to Turkey transportation time could be reduced from a month to 12 days as part of the Iron Silk Road concept.[29]

That the tunnel construction is only about 18 kilometres (11 mi) away from the active North Anatolian Fault has worried some engineers and seismologists. "Since AD 342, it has seen large earthquakes that each claimed more than 10,000 lives."[12] Some scientists have estimated a 77% probability that, at some time in the next 30 years, Istanbul will suffer an earthquake measuring 7.0 or more on the Richter magnitude scale. The waterlogged, silty soil on which the tunnel is constructed has been known to liquefy during an earthquake so engineers injected industrial grout to 24 metres (79 ft) below the seabed to keep it stable.[12] The walls of the tunnel are made of waterproof concrete coated with a steel shell, each section independently watertight. The tunnel is made to flex and bend in the way that tall buildings are constructed to react if an earthquake hits. Floodgates at the joints of the tunnel are able to close and isolate water in the event of the walls' failing.[12]

Steen Lykke, project manager for Avrasyaconsult, the international consortium that oversaw the construction, summed the problems up by saying, "I can't think of any challenge this project lacks".[12]

Some figures of the project are as follows:[28]

• Overall length: 76.6 km (47.6 mi)
• Tunnel section: 13.6 km (8.5 mi)
• Immersed tube: 1,387 m (4,551 ft)
• Deepest point: 60.46 m (198.4 ft)
• Minimum curve radius: 300 m (980 ft)
• Maximum gradient: 1.8%
• Surface stations: 37
• Underground stations: 3
• Interchanges: 8
• Inter-city stations: 8
• Minimum platform length: 225 m (738 ft)
• Average station spacing: 1.9 km (1.2 mi)
• Maximum speed: 100 km/h (62 mph)
• Commercial speed: 45 km/h (28 mph)
• Headway: 2–10 minutes
• Passengers per hour and direction: 75,000
• Number of passenger cars: 440

• Eurasia Tunnel
• Great Istanbul Tunnel, a proposed three-level road-rail undersea tunnel
• Public transport in Istanbul
• Rail transport in Turkey
• Turkish Straits

Wikimedia Commons has media related to Marmaray.

• Official website
• Overview of the Marmary history, justification, and construction process with pictures
• Marmaray Project:
  • L. C. F. Ingerslev, 2005, "Considerations and strategies behind the design and construction requirements of the Istanbul Strait immersed tunnel," Tunnelling and Underground Space Technology 20: 604–08.
  • Steen Lykke and Hüseyin Belkaya, 2005, "The project and its management," Tunnelling and Underground Space Technology 20: 600–03.
  • Steen Lykke and Frits van de Kerk, 2005, "Marine operations, the Bosphorus Crossing," Tunnelling and Underground Space Technology 20: 609–11.
  • Hideki Sakaeda, 2005, "Tunnels and stations in BC contract," Tunnelling and Underground Space Technology 20: 612–16.
• Gokce, Ahmet; Koyama, Fumio; Tsuchiya, Masahiko; Gencoglu, Turgut (2009). "The challenges involved in concrete works of Marmaray immersed tunnel with service life beyond 100 years". Tunnelling and Underground Space Technology. 24 (5): 592–601. doi:10.1016/j.tust.2009.01.001.
• Istanbul Technical University Marmaray Laboratory web site.
• Tunnelbuilder technical description.
• (in Turkish) Marmaray BC1 project and surveying works
• BBC article on the project.