Sea and seismicity

In order to reduce congestion over a 2.3-mile-wide waterway separating Europe and Asia, known as the Bosphorus, the Turkish government is constructing the 3-mile Istanbul Strait Tunnel 360 feet below sea level. Construction has faced a unique set of risks, with extreme water pressure combined with the location's propensity for seismic activity, as well as the tunnel's large diameter, double-decker configuration. The use of one of the most sophisticated tunnel boring machines (TBMs) ever designed was a necessity, with the slurry-shield TBM specifically designed for the geotechnical conditions and extreme water pressure present. Details of the design and construction are presented.