During the design phase of all tunnels, short and long-term deformations are predicted, based on the results of numerical calculations. These values have to be based on engineering experience as well as on measurements from previous projects. In the early 1980’s, the first NATM driven metro tunnels in soft ground were built in Vienna by Wiener Linien. The behavior of Vienna´s soft ground due to the application of NATM was subject to investigation. Detailed monitoring systems were implemented. Starting with the period of construction until nowadays, these measurements were taken by Wiener Linien in order to gain information about the long-term behavior of NATM tunnels. This investigation is based on data from lot U6/1 "Pottendorfer Strasse" back from 1986 until today. Meanwhile a systematic safety management has been installed for all underground structures covering all phases of the life cycle. The lot U 1/10 "Troststrasse", currently under construction, is used as an example.
1 Selected Construction Sites
Vienna’s metro network currently consists of 69 km running and platform tunnels of which 26 km are NATM tunnels, 11 km are TBM tunnels consisting of 7.7 km cast iron segments and 3.2 km precast concrete segments. The remaining tunnels in the network were constructed with the cut and cover method. Railway infrastructure requires detailed safety monitoring through all phases of a tunnel’s life cycle. The article shall focus on the processes, which are implemented in the design and construction phase, but also on the processes, which take place after starting service/railway operation in tunnels.
1.1 Metro construction in Vienna in the 1980’s
In 1981, the general design plan for metro line U6 was issued by the city of Vienna. It proposed the extension of the existing light rail system, which was in operation since 1898. With the new line name "U6", the light rail system should be extended to the south of Vienna, connecting residential areas to the center of the city. The construction site called U6/1 "Pottendorfer Straße" was the first major project in soft ground in Vienna using NATM.