Asia Transition Box and Conventionally Excavated Twin Tunnels for the Istanbul Strait Road Crossing Project

The 14.6 km long Istanbul Strait Road Crossing Project is a safe, quick and environmentally responsible alternative road link between Asia and Europe, as such it is being constructed under a Build-Operate-Transfer contract by a public-private partnership. The investor/contractor has committed to build the Project in 55 months and to operate the facility for a concession period of approximately 25 years. This article examines the project's two critical structures located in the Asian side of Istanbul, considering site investigation, construction and monitoring. The first structure is a cut and cover construction next to the Bosphorus, called the Asia Transition Box (ATB), which enabled the launching of the TBM and conventional tunnels. The second is the conventionally excavated twin tunnels (CETT), which pass under a highly urbanized part of Istanbul and provide the transition from the highway into the tunnel under the Bosphorus.