Tunnels of Metro Vienna
Abstract: Vienna has a long tradition in Metro Construction dated back to the end of the 19th century, when the „Vienna Stadtbahn“ was established, well known for the design of architect Otto Wagner. At the end of the last century the urban traffic increased so heavily that tram and bus couldn’t solve anymore the problems of public traffic needs. In 1970 the first working lot “Karlsplatz” situated in the centre of the city was opened, followed by different working fields along the Metro Line U 1. The tunnels were established by shield machines of that time supported by compressed air and soil grouting to tight up the water bearing sediments of the ground of Vienna. In the following years the Metro Lines U 4 and U 6 where designed to renew the old public system of the Stadtbahn upgrading the stations and running tunnels equipped with new electric traction and operating services. In 1984 the Metro Line 3 the second transversal line was started adopting NATM for urban area, combined with dewatering systems with groundwater wells outside the tunnels and deep excavation between cut and cover walls. Also compressed air and soil grouting was used for tunnelling under densely populated residential area and nearby architectural well known buildings like St. Stefan Cathedral respectively (1., 2., 3. 11.). In the last ten years the metro net was enlarged with extensions of all lines especially of line 1 and 3. During this decade also the underpass tram Line 2 as a halve circle line beneath the “Lastenstraße” parallel to the Vienna Ringstraße was upgraded to the Metro Line 2 starting at the well known Musikverein palace running to the Vienna main stadium. This is situated in the park of Prater where the soccer championship of 2008 took place. The Metro extensions opened challenges for up-to-date soil construction techniques with deep foundation engineering like soil freezing, halve and full crown support by horizontal jet grouting rings, well dewatering for large fields down to ten and fifteen metres limited by tight walls from other Metro Lines interrupting the ground water flow during working period (10., 11.).