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Eurasia Tunnel (Istanbul Strait Road Tube Crossing)

First road tunnel construction in the Bosphorus linking Europe and Asia: innovation and international collaboration solve technical challenges.

Only city settled on two continents; the modern-ancient city of Istanbul dates back to 660 BC and is now one of the most populous in the world with over 15 million people. The first road tunnel crossing of the Bosphorus in Turkey will provide an important transportation link between the European and Asian sides of Istanbul, reducing travel time from 100 minutes to 15 minutes. It is part of a 9 mile (14.6 kilometres) highway project.

Boring machine - Eurasia tunnel

CLIENT OBJECTIVE AND PROJECT CHALLENGES

Four lanes of roadway will pass in stacked upper and lower decks through 3.3 miles (5.4km) of tunnel. This includes a 45 foot diameter (13.7 metre) bored submarine tunnel over 2 miles (3.4km) long and twin New Austrian Tunnelling Method (NATM) tunnels, each 0.6 miles (1 km). At depths of 330 feet (100m) below the water surface, in sand and gravel, the single pass segmental lining will be required to resist 11 bars of water pressure and large seismic forces. Construction also requires tunnelling through poor quality rock at both the Asian and European sides of the crossing, and mixed-face conditions beneath the Bosphorus. Special attention had to be given to design of the bored tunnel lining segments, gaskets, and bolted connections.

The significant technical challenges faced by the designers and builders are coupled with both obstacles and opportunities brought together by the multinational design and construction teams. The design and construction coordination was accomplished with support by staff in Turkey, Korea, Great Britain, Austria, and the United States. The construction drawings were bilingual, Turkish and English; and the design was required to meet Turkish, European, and American codes.

Eurasia Tunnel

APPROACH

A series of tunnel types, including cut-and-cover, sequential excavation, and bored tunnels, were used to optimize cost and minimize construction time. The combination of tunnel types made the most appropriate use of each different tunnelling technique and allowed multiple faces to be excavated simultaneously. The bored tunnel accounted for approximate 75 percent of the combined length of the tunnel. A stacked roadway structure was designed within a single large bored tunnel to reduce construction and maintenance costs and improve reliability and fire-life safety.

Two innovative seismic joints designed by Seibu Polymer and NCC from Japan were incorporated into the bored tunnel lining to allow flexibility and accommodate the movements predicted by a rigorous seismic analysis of site specific conditions and structure configuration. The seismic joints were installed with the tunnel boring machine (TBM) and located at the approximate one-third points of the tunnel near the interfaces of the soft marine deposits and rock. A 45 foot (13.7m) diameter Herenknecht mixed-shield slurry TBM was used to mine the tunnel under the Bosphorus without serious difficulties. Sequential excavation (NATM) tunnelling was used for 0.6 miles (1 km) of the twin tunnels, with mined cross passages. Cut-and-cover construction was used at the approaches. 

The design was scheduled and completed on a “just-in-time” basis in support of construction.

OUTCOME

The tunnels were successfully constructed without major incidents or interruptions. Currently, we are in the project's final stages: installation of the finishes and roadway decks.

The tunnel is scheduled to open ahead of schedule, on December 20, 2016.

This project has won the 2015 Tunnelling Project of the Year award from the International Tunnelling Association (ITA) and the ENR’s Global Best Project in the Bridge/Tunnel category (2016).

SERVICES PROVIDED

Planning, conceptual design development, preliminary design documents, and detailed design (drawings, specifications, and design reports) for:

  • Tunnel and roadway alignment
  • Tunnel alignment and configuration
  • Mechanical and electrical system design for ventilation, traffic control, and fire and life safety systems
  • Tunnels’ structural design, caverns, excavation support, and tunnel segmental lining design
  • Europe permanent transition structure and permanent stacked structures on European side
  • Transition structures support of excavation design on both sides of TBM tunnel

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