Examples of project optimisations for the Vienna underground upgrade at the U2/21 ‘Neubaugasse’ construction lot

This article presents the optimisations made during the planning phase regarding the construction in the tunnelling concept for construction section U2/21 “Neubaugasse”, as well as the insights gained for future applications in the construction of the Vienna subway system. As part of the subsequent planning of the general project, the existing data was analysed in detail, potential for optimisation was identified, and the planning was refined. In this phase, further optimisations were identified based on different perspectives on the project. Based on a 3D subsurface model developed in advance by MA29 and the resulting geological and hydrological conditions, the tunnelling works in this section predominantly take place in Miocene strata with water‐bearing sand lenses. Since one station tunnel lies entirely beneath densely built‐up areas and no surface drainage was possible, an innovative tunnelling concept was developed. This concept includes a pilot tunnel constructed in advance using fibre‐reinforced shotcrete. Further optimisations included both the structural design and construction logistics. In addition to optimising the station cross‐sections, raising the alignment of the station structure helped reduce the life cycle costs of the structure, particularly in terms of operation and maintenance. Additionally, logistics concepts were reviewed to improve the construction process, along with approaches for material processing.