The new S4

How does the jet grouting method work?

Put simply, a cement mixture is worked into the ground to create stable columns underground. The process works as follows:

• First, the soil is moistened so the materials can be distributed more effectively.
• Then, a cement mixture is injected into the ground through a drill rod.
• This creates a solid, circular cement column that stabilizes the subsoil once it has hardened.

This procedure is repeated at many points. The individual columns partially overlap and merge into a continuous, stable foundation.

For anyone who would like a clearer picture of the process, our partner Keller shows in the following short video how jet grouting works:

https://www.youtube.com/watch?v=u2MtF90NMXk

Stability is created below the surface

During these works, it may often look on the construction site as if not much is happening. In reality, this is precisely the phase in which the foundation for the future railway line is being created underground.

Depending on the area and requirements, the cement columns can be produced in different sizes. They can be extended vertically, for example to form a support or wall, or arranged horizontally to form a surface, such as the base of an excavation pit.

Why do we use jet grouting?

The jet grouting method offers several advantages – especially for construction projects in urban areas:

• It works in many different soil types.
• The equipment is relatively compact, making it well suited for construction sites with limited space.
• Only the soil layers that actually need stabilization are reinforced.
• The method is often faster than other techniques and can help shorten construction time.

With methods like jet grouting, a stable subsoil is created step by step – the essential foundation for the future S4 S-Bahn line.

Construction Progress in Section 1

Significant progress was made in the first construction phase in 2025. At the Hasselbrook rail junction, work on the grade separation structure progressed considerably. In the northern section, the floor and walls of the future railway tunnel have already been completed using reinforced concrete. In the central section, the frame structure, which will later support the railway line running above, is under construction. An underground concrete slab has been installed here to ensure the structure will be watertight. Currently, tiebacks are being installed to guarantee structural stability.

Work has also progressed visibly in Wandsbek. The first bridge superstructures arrived at Bovestraße. These are prefabricated in the workshop and then welded together on site. Simultaneously, service walkways and central supports are being built so that the bridge can support the new S-Bahn station.

At Luetkensallee, the track work has been completed, the subsoil stabilized, and the necessary preparations made for the construction of the extended pedestrian underpass. The dismantling of the old structures is now underway, before the excavation pit is sealed in early 2026 and construction of the new frame structure begins in the spring.

The trial operation of the transparent MetaWindows continues successfully. More than 900 square meters of these transparent noise barriers have been erected since October 2024 as part of the operational testing. The analysis of the most recent inspection is currently being compiled. Preliminary results already show that the noise-absorbtion on the track side is just as effective as that of the traditional aluminum elements.

Planning for construction phases 2 and 3 as well as for the individual measures

In the second planning approval phase, we also made significant progress in 2025. In March, the third amendment to the plans was finalized and publicly announced. Those affected by the amendment then had another opportunity to submit objections. In October, the public hearing process concluded, and the hearing report was received. This report compiles the objections thematically and categorizes them from a technical perspective. The planning approval authority uses the report as a basis for its decision on the planning approval or to identify necessary revisions to the plans.

There were also positive developments in the third planning approval phase. Practical solutions were found for issues raised in the submitted objections, and these are currently being incorporated into the planning documents. At Ahrensburg West, boreholes were drilled to examine the subsoil more closely and to prepare the geotechnical report. At Brauner Hirsch, alternatives were examined that avoid archaeologically valuable areas and thus require significantly less disturbance to the ground. The environmental documentation has also been further developed: Important information was obtained through re-mapping of fauna (wildlife) and biotopes (habitats).

Particularly pleasing: the planning approval for the individual project in Bad Oldesloe has been in place since November.

The experience gained from the construction work in Wandsbek is also providing important foundations for the upcoming construction phases. Findings from soil stabilization, bridge construction, and noise protection are being incorporated into further planning.

Public relations

2025 was also a very active year in terms of communication. Numerous visitors participated in our public construction site tours during the summer. At the UITP Summit, the S4 presented itself as a flagship project for Hamburg and also offered international guests an exclusive technical tour of the construction site. On Rail Day in September, the project team organized two special tours with an S4 bingo game – afterwards, the information train invited participants to chat over coffee and cookies.

The information train is now taking a winter break until the end of January 2026 and will then reopen with adjusted hours. Learn more about the information train here.

Further impressions and background information on the project can be found at any time in our project diary.

Progress was also made in the planning phase: Soil investigations, feasibility studies, and the planning approval for Bad Oldesloe provide a solid foundation for the upcoming construction phases. Events such as site tours and our information train further strengthened communication with the public.

With this foundation in place, we look forward to 2026: Further construction progress, planning decisions, and an open dialogue with all stakeholders are on the horizon. We thank you for your trust and wish you a peaceful Christmas season and a happy New Year.

Here's to continued successful collaboration!

— Bernd Homfeldt, Head of S4 & ABS Pinneberg-Elmshorn