The Extension of the U5 – Geotechnical and Structural Challenges

The construction of the new U5 underground line marks a very challenging milestone in the development of the Vienna underground. Planned are inner‐city stations and operational buildings, constructed using the cut‐and‐cover method, as well as approximately 4.5 km of tunnel excavation carried out beneath existing buildings using both conventional (NATM) and mechanised tunnelling methods. Due to the varying geological conditions, such as thick water‐bearing and pressurised sand layers, extensive geotechnical measures are required, demanding solutions that are adapted to the local ground conditions. In addition to tunnelling beneath existing buildings, another challenge is the restricted space available for the construction of shafts. This calls for a sound, engineering‐based assessment and safety management of the structures within the tunnel's zone of influence, as well as a logistics and traffic concept coordinated with all stakeholders.