The Eurasia tunnel connects the Asian with the European side of Istanbul in the form of a twin-level tunnel underneath the Bosporus. IGT planned the NATM tunnel sections on the Asian side and the construction pit of Asian Transition Box ATB located right next to the sea, which was used as both the starting pit for the TBM tunnel and for the NATM counter-heading.
The NATM tunnel tubes are routed within the sediments of the Trakya formation below the ground water level and have therefore been planned to be pressure water-resistant. In the area of the transition structure (ATB) from the 2 NATM tubes to the twin-level tunnel, walled-shaft heading and pipe arches were required due to the confined space; these had been planned by 3D FE calculations. A special challenge represented planning of the 170 m long, up to 36 m wide and up to 40 m deep ATB construction pit.
Basic and Detail Design:
Excavation & Support for ATB and Cut&Cover tunnels
NATM tunnels approx. 1900 m,
of which approx. 280 m in pipe arch heading
ATB construction pit approx. 170*36*40 m
Cut&Cover construction pits for both NATM tubes