Marmaray Runs Trains Under the Bosphorus

On October 29, 2013, Turkish officials inaugurated the central undersea section of the Marmaray rail project, creating a direct railway connection beneath the Bosphorus strait. Opening on the ninetieth anniversary of the Turkish Republic, the line established the first standard-gauge rail link between Europe and Asia, where earlier connections across the continents had depended on incompatible Russian broad-gauge tracks. The ceremonial opening completed the most technically demanding phase of a larger regional modernization program, intended to connect the European terminal at Halkali with Gebze on the Asian side through a continuous seventy-seven-kilometer commuter corridor.

The subsea passage relied on a 1.4-kilometer immersed tube resting sixty meters below sea level, which made it the deepest immersed tube tunnel in the world. Assembled from eleven prefabricated concrete sections weighing up to 18,000 tons each, the tube was laid in an undersea trench beneath fifty-five meters of water and several meters of seabed sediment. Bored approach tunnels linked the submerged tube to Kazlicesme on the European shore and Ayrilikcesmesi on the Asian shore. Because the Bosphorus runs roughly eighteen kilometers from the active North Anatolian Fault, builders stabilized the liquefiable seabed by injecting industrial grout down twenty-four meters, protected the concrete sections with waterproof steel shells, engineered flexible joints, and installed floodgates to seal off breaches.