This project is named ‘Marmaray’ which is a rail transport project in Istanbul, Turkey. The name ‘Marmaray’ comes from combining the name of the Sea of Marmara, which lies just south of the project site, with ‘-ray’, the Turkish word for rails. It is an undersea railway tunnel passing under the Bosphorus Strait. Existing suburban railways of approximately 76 kilometers are to be modernized. Tunnels and stations in 13.6km length of this project have been constructed by immersed-, shield- and mountain- tunneling methods together with a cut-and-cover technique. Construction had started in 2004 and the tunnels and stations have become in service since October 29, 2013. In this paper, the construction of an underground railway station (Sirkeci Station) in an urban area consisting of neighboring large-scale tunnels and shafts by means of NATM is reported.
Sirkeci Station has two ventilation shafts (about 510m2 in cross-sectional area) at both ends (west and east side) of the station. The shafts are connected with two platform tunnels (about 190m2 in cross-sectional area). Each shaft is neighbored to the platform tunnels at a minimum interval of about 1m.
First of all, the west shaft was excavated and supported with steel rings, columns and additional shotcrete in order to reduce the influence of four openings at the shaft and neighboring tunnels excavation.
Prior to the east shaft excavation, the tunnels were excavated and supported by reinforced-concrete primary lining. Subsequently, the shaft adjacent to the tunnels was excavated. Lastly, the shaft and platform tunnels were connected with additional supports such as additional shotcrete, forepiling, etc.
Before the influencing events, three-dimensional excavation analyses were carried out in order to decide the specification of the additional supports. Through the analyses, the support behaviors due to the events were predicted.
During the excavation, the monitoring results were compared with the prediction. To ensure the stability of structures and ground around the shafts and tunnels, observational construction management is indispensable. The measured results that were within the allowable limits successfully proved the stability of the complex structures of the underground station.