In the section of the Hamburg U3 subway line between Baumwall and the main railway station, several tunnel structures needed to be repaired. Over time, they had sustained major damage to their steel girders and supports as well as to concrete components. This was mainly due to cross-sections weakened by corrosion of steel components as well as reduced strength, moisture penetration, efflorescence, cracks, and spalling in the structural concrete. The 861-metre-long tunnel section was thus weakened in its stability, operational safety, and durability.

A holistic rehabilitation concept was developed by means of status-quo surveys and investigations as well as static recalculations. On the tunnel side, damaged steel components were being restored and some of the tunnel walls were being strengthened with reinforced and anchored shotcrete. The tunnel floor was also being reinforced in some sections. In addition, individual areas with moisture penetration were being sealed from the inside by means of injection techniques. To tackle the large-scale moisture penetration in the tunnel ceiling, the sealing layer was being renewed from the outside.

In parallel to the tunnel repair, extensive construction work was taking place on the Rathaus and Mönckebergstrasse subway stations, which were erected in 1906 and 1908 in open cut tunneling Alongside measures for barrier-free development and modernization, structural components were being repaired here, too.