Line Ⅱ of Warsaw Underground: the excavation of tunnel connector (Centrum Nauki Kopernik station) under existing Wislostrada tunnel

摘要

The Centrum Nauki Kopernik station of the Line Ⅱ of the Warsaw Underground is located along and close the Vistula river. The station consist of three parts: the east and west shaft and one connecting tunnel of large cross section (170 m~2), which includes the rails along the sides and the platform along the center. The reason for the underground connection of two shafts with a tunnel is due to the presence of a road tunnel, which must be underpassed by the new metro line. The existing tunnel (Wislostrada) was built between diaphragms walls by top-down method and some foundation parts of its structures interfere with the underground tunnel. The challenging target was to build the connectors without stopping the traffic of vehicles along the above highway. All works have occurred in very difficult geological and hydraulic conditions due to uie presence of Vistula alluvial deposits of poor mechanical characteristics. In particular the soil profile consists of upper relatively loose sands and silts overlying the Pliocene high plasticity clays strongly disturbed by the effects of repeated over sliding of the glacial moraine deposits. In order to carry out the work in high safety conditions, it was decided to improve the poor soils by cement-chemical injections and freezing method using liquid nitrogen and brine. An extensive monitoring system was installed in order to control in continuous mode stress-strain state of each structural part of the highway and of the station. In this paper are shown finally the comparison between the expected results from design and the observed behavior of the structures.