Within the scope of Eurasia Tunnel Project (Istanbul Strait Road Tube Crossing Project) that connects Asian and European continents with highway tunnel under seabed for the first time; excavation support systems of temporary structures called as transition boxes and prepared for TBM (Tunnel Boring Machine) entrance and breakout points were executed in both European and Asian sides.
The Eurasia Tunnel, between Kazlıçeşme and Göztepe line where the vehicle traffic is very heavy, has a route of 14.6km. A total of 5.4 km part of the project consists of two-storey tunnels, constructed with a special technology under the seafloor, and connection tunnels, constructed with other methods. TBM (Tunnel Boring Machine), specially designed for this project was the 6th in the world with an excavation diameter of 13.7 meters, was successfully used in this project Roads were expanded and improved in 9.2 kilometers of routes both in European and Asian sides. In addition, the approach roads between Sarayburnu-Kazlıçeşme and Harem-Göztepe were expanded and vehicle underpasses and pedestrian overpasses were completed.
Asian Transition Box (ATB) Excavation Support System Works
For the excavation support system of Asian Transition Box; anchors with an individual length of 20 m to 42 m with a total length of 83,250 m, secant piles with a total length of 21,000 m, rock bolts with a total length of 10,200 m were constructed including other geotechnical works. The geometry of excavation was rectangular with dimensions of 170 m x 25 m in plan. The maximum depth of excavation was 40 m and the volume of excavation was ~140,000 m³. Soil profile consisted of uncontrolled fill with a depth of maximum 10m and underlain by extremely weathered greywacke including fault breccia. Pile and diaphgram wall reinforcements; rock bolts were constructed by using fiber glass reinforcements at TBM and NATM Tunnel entrance; TBM exit locations.
- Deep excavations up to ~40 m very close to the Sea of Marmara were successfully completed without damaging surrounding roads and structures
- Periodically, displacement and anchor load measurements were made at each stage of the project and necessary measures were taken at stages where and when design criteria differed
- In TBM and NATM entrance locations, rock bolts were used instead of prestressed anchors.
European Transition Box (ETB) Excavation Support System Works and Yenikapı Underpass and U-Turn Structures Geotechnical Works
The shoring design consisted of diaphragm walls laterally supported with steel and reinforced concrete struts. An impermeable block was established with unreinforced piles to prevent water flow from TBM exit area during breakout operation. This impermeable block is important for its being one of the biggest impermeable block in Turkey. The dimensions of rectangular transition box excavation was 70 m x 30 m in plan whereas, the dimensions of rectangular substation building excavation was 45 m x 45 m in plan. Moreover there is a Cut and Cover Section having a total lenth of ~600 m. Furthermore, underground support system was established by using unreinforced walls due to large lateral displacements coming from the excavation base.
Within the content of the project, diaphragm walls with a thickness of 100 cm to 150 cm and a total area of 45,200 m² were constructed. Additionally for TBM exit face in this location, an impermeable wall was established with unreinforced secant piles having a total length of 19,500 m and a diameter of 120 cm and jet grout columns with a total length of 6,000 m were installed. The maximum excavation depth is ~30 m. Fiberglass was used in diaphragm wall constructions at TBM exit location in order to prevent any damage that can be given to TBM equipment during excavation.
Within the scope of Yenikapı Pedestrian Project, barette piles with a total area of 12,200 m²; diaphragm walls with a total area of 14,900 m² and jet grout columns with a total length of 114,200 m were constructed.
- Deep excavations of up to 30 m in a region only 25m-30m far away from the Sea of Marmara were successfully completed without damaging surrounding roads and structures
- Periodically, displacement were measured at each stage of the project and necessary measures were taken at stages where the design criteria differed.