UNDERGROUND CONNECTIVITY (EURASIA TUNNEL IMPROVES CONNECTIVITY BETWEEN TWO CONTINENTS AND HELPS RELIEVE ISTANBUL’S CONGESTION)

                                                              

UNDERGROUND CONNECTIVITY (EURASIA TUNNEL IMPROVES CONNECTIVITY BETWEEN TWO CONTINENTS AND HELPS RELIEVE ISTANBUL’S CONGESTION)

Associated Research Centers for the Urban Underground Space (ACUUS)
Solution proposed by: 
ACUUS and ATAS (The Concessionaire)
In a Nutshell: 
Eurasia tunnel eases traffic congestion under the Bosphorus Strait and provides for an alternative yet very important road link between wide network of highways of the eastern (Asian) and the western (European) parts of Istanbul. The project provides for a blueprint for all future PPP infrastructure projects in Turkey.
Where and When: 
The project is being implemented in Istanbul, Turkey. It started in 2011 and is anticipated to open to traffic in 2017. The Eurasia Tunnel will provide a direct connection between the highway networks on the two sides of the city, and between the two airports, bypassing congested streets.
Challenges: 
The main challenge for the project implementation is the ability to fund the capital cost of $1.245B. Using a PPP approach the concessionaire entered into agreement with the Ministry of Transport to build, operate and transfer (BOT) for a concession period of 26 years. The technical challenges of the crossing included the construction in very congested and historical urban areas, utilization of new technology-large diameter tunnel boring machine (TBM), high water pressure under deep water crossing, all within the region with high seismic propensity. These challenges had to be addressed in order to be able to construct the facility.
Innovation: 
To address the above urban challenges, the tunnel was designed with double deck to accommodate passenger vehicles and mini-buses only, providing easy connections to commuters. The double deck tunnel is an innovative approach that has rarely used previously and never for crossing under the body of water. The underwater tunnel passes through weathered bedrock on either side of the Istanbul Strait and through alluvial deposits including sand and gravel near mid channel. To deal with seismic requirements in terms of safety and operability, two seismic joints were designed to absorb ± 50 mm in transverse displacement and 75mm in longitudinal movement
Concept: 
To meet the project needs in term of traffic improvement, reduction of congestion, reduction of emission and pollutants, and to maintain the silhouette of the historic part, a deep tunnel was selected for the crossing. The overall project consists of three parts totaling 14.6km. Segments 1 and 3 consist of widening existing motorways, providing connections to existing roads, reconstructing local bridges and underpasses. Segment 2 is the tunnel crossing beneath the Bosphorus Strait. With a total investment of $1.245B, of which about $300M is in equity, the concessionaire ATAS, consisting of Yapi Merkezi from Turkey and SK E&C from Korea, is committed to start the tunnel operation within 48 months from the financial closure which took place in March 2013. The construction started on Asian side and accomplished a successful work on European side in August 2015 with the tunnel boring machine (TBM) breakthrough. That unique TBM was built for the project to excavate the tunnel to a depth of 106 m below the water surface requiring it to resist 11 bars of hydrostatic pressure and up to 22 bars of hydrodynamic pressure during an earthquake. All risk work elements involving various tunneling works were successfully completed ahead of their schedule.
Description: 
The intent of the project is to provide a direct and easy connection between the Anatolian (Asian) side of Istanbul and the heart of its historical district on the European side across the Bosphorus Strait which connects the Black Sea with the Sea of Marmara. The overall project consists of three parts. Segments 1 and 3 mainly contain widening of the existing motorways, providing connections to existing roads, and reconstructing local bridges and underpasses on the European and Anatolian sides, respectively. Segment 2 is the tunnel under the Bosphorus; it is the most complex part of the project with the greatest challenges and risks. That segment is 5.4 km long, consisting of 3.4 km of 13.2m external diameter tunnel under the Bosphorus Strait, 1-km of twin approach tunnels on the Asian side (to be constructed using New Austrian Tunneling Method), cut and cover transition boxes in the Asian and the European sides, and the tunnel approaches on both sides. In addition, this segment includes the toll plazas, ventilation buildings, and the tunnel control and maintenance facilities. The tunnel nominal inside diameter of 12.0m provides space for two 3m wide travel lanes in each direction and a 1.2 m wide emergency egress at each level. The 3m vertical clearance allowed for cars, vans, and mini busses. Emergency egress stairways were provided every 200m into pressurized stairwells connecting the upper and lower roadways; and vehicular breakdown alcoves were provided every 600m. Fire life safety aspects had been met through longitudinal ventilation via jet fans in the ceiling of each roadway supplemented by two ventilation buildings. In addition, all other essential elements including traffic control, lighting, communication, etc. were provided in each traffic level.
Impacts: 
On target for the full completion in March 2017, this new 14.6 km long transportation project will increase capacity across the Bosphorus by 100,000 vehicles per day, reduce congestion and save motorists an average of 45 minutes of commuting time in each direction. It will bring significant economic benefits to the city and the region, decrease pollutants and emission while maintaining the historical silhouette of the city. Upon its opening day, the project will meet its benefits in terms of connectivity of the City neighborhoods spreading on two continents, improving mobility of its citizens, providing for commuting time saving, and ensuring the extensive environmental and economic benefits to the entire metropolitan region.

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Yapi Merkezi / SK-E&C. Also,  a 9 p. Power
Yapi Merkezi / SK-E&C. Also,  a 9 p. Power