2nd Regional Train Main Line Munich, Exciting Milestone at Construction Site Marienhof

At construction site Marienhof, one of the three new stations of the 2nd regional train main line in Munich, exciting progress has recently been made. Deep under, the steel supports of the temporary reinforcement level -5 are currently pretensioned and the air pressure chamber at level -3, required for digging of the connecting tunnel to the underground station of U3/U6, has successfully put into operation.

Erection and pretensioning of the temporary reinforcement level -5

At a depth of around 35 metres, the temporary reinforcement level -5 is currently being pretensioned. This level consists of a circular reinforced steel frame and steel supports made of round hollow profiles as well as welded together rolled steel profiles.

The temporary reinforcement level plays a significant role during the construction process: It is required to implement the last excavation section until the lower edge of the future floor slab. It stabilises the diaphragm wall and distributes horizontal soil pressure loads. As soon as the first part of the floor slab is completed, the reinforcement level will be completed removed. Subsequently, the loads are redistributed to the floor slab and the ceiling of level -4.

From the middle until the end of 2024, the temporary reinforcement level -5 was built section by section: Firstly, the circular reinforced steel frame was concreted and then the steel supports and presses were put into position; finally the crossing points were concreted.

On 16 January 2025, another important milestone started – the pretensioning of the steel supports. A precisely elaborated pretensioning concept provided an even and structurally advantageous distribution of loads onto the load-bearing structure. During the entire pretensioning process as well as the following excavation works, the deformations of construction elements – including the supports, hubs and diaphragm walls – are carefully monitored through a specially developed monitoring concept.

Pretensioning will be completed on time until the end of January 2025. Subsequently, excavation underneath level -5 will begin. Here, excavation is also done by sections to ensure a symmetric deformation of the reinforcement grid and to distribute loads evenly.

Pressure chamber level -3: progress at the connecting tunnel to underground stations U3/U6

Another milestone at the construction site Marienhof is the construction of the connecting tunnel which links the new station to the existing underground station Marienplatz (U3/U6). The tunnel is built by air pressure shield. A specially designed air pressure chamber was erected at level -3 for this purpose, which provides positive pressure of 0.8 bar (during standard operation).

The pressure chamber is exclusively required for the construction of the tunnel’s outer lining and will be completely removed after completion of the works – expected in August 2026. The tunnel’s inner lining will then be built under atmospheric pressure.

The design of the mined tunnel is produced by our partner INGE-Partner ILF, and SSF has designed the pressure chamber at the station’s structure as well as the transition block to the mined area. The reinforcement of construction elements was planned by 3D-Rebar in Revit. Especially for the complex geometry of the transition block, 3D-Rebar offers great advantages compared to conventional 2D designs.

On 15 January 2025, the symbolic groundbreaking of the tunnel took place. Our colleagues from SSF participated at the ceremony to experience live and on site this significant moment.

Currently, the first test operations of the pressure chamber are carried out during which the tightness of the chamber and the safety concept have successfully been verified by TÜV. During operation, the pressure chamber is accessible via a personnel airlock as well as a large-device airlock. The material excavated during tunnelling is removed via troughs through the large-device airlock. The pressure chamber is efficiently supplied with materials like sheets and spits via a separate material airlock.