Istanbul Strait Road Tube Crossing
Bosporus Tunnel, Turkey

This project was realized by IGT.

Istanbul is a metropolis of several million inhabitants, where space is at a premium. the Eurasia Tunnel links the Asian and European sides of Istanbul with a double-decker tunnel under the Bosporus. The project aimed to relieve traffic in the city. The tunnel results in avoidance of traffic jams and reduces commute times between the two parts of the city to less than 15 minutes.
The tunnel is situation 106 m under the sea and has capacity for approximately 60,000 vehicles.

IGT designed the NATM sections on the Asian side and the box excavation immediately adjacent to the sea (Asian Transition Box – ATB), which served as the launch box for the TBM tunnels, and the start point for the NATM drive and presented a particular challenge.

The 170m-long, up to 36m-wide, max. 40m-deep ATB was excavated through man-made deposits and decomposed rock before reaching the more competent sedimentary Trakya Formation at lower depths. The top section of the box was constructed within a watertight secant pile wall, the lower section with a discontinuous pile wall, each retained with strand anchors. Following the TBM drive, the box was used as the transition structure from the NATM tunnelst o the double-decker TBM tunnel.