A power team for the Marienhof project

New construction 42 metres underground

But beneath the former green space at Marienhof, nothing is what it was. Embedded in six alternating sequences of tertiary clays and sands, 200,000 cubic metres of reinforced steel will carry a construction that stretches up to 42 metres underground and will improve the infrastructure for Munich’s local public transport in a sustainable way. The new commuter rail station is part of the 10-kilometre second trunk section that crosses the centre of Munich largely underground – from Laim in the West to Leuchtenbergring in the East – passing under houses and business, churches and museums, and even existing stations and tunnel systems for the current underground and commuter railways.

No one has ever dug deeper in Munich

The crowded space underground has forced the construction companies to dig deeper than anyone in Munich has ever done before – an undertaking made all the more difficult by the crowded space above ground. “One of the biggest challenges in this project full of challenges is logistics,” stresses Jens Classen, who heads the Marienhof syndicate as overall project manager. “We are bringing enormous machinery into extremely tight spaces in the centre of a very busy city, ideally without being seen and, above all, heard.” “Anyone who wants to build here needs to be proactive in their efforts to nurture good relations with their neighbours,” adds Michael Müller, Construction Manager and deputy overall project manager.

One example he mentions is the city’s mayor, whose office is in the town hall next door. “We talk to each other all the time. Today, for example, the Bettenrid store is having new shop windows delivered in the central courtyard directly opposite, blocking our access to the north of the site. We need to find a solution.”

Complexity at every level

Finding solutions is the central theme of this project, which unites the two major construction and real estate corporations in a joint venture. This joint venture in turn works closely together with the client, Deutsche Bahn, and numerous subcontractors.

“It is rare for a construction site to bring together so many different disciplines and for every single one of them to face such enormous challenges,” says Michael Müller, describing the complexity of the project. In the first phase of the construction project, Special Foundations had to erect 15,700 square metres of diaphragm walls and 50 primary supports extending up to 67 metres into the ground.

Constant measurements and stabilisation measures

To ensure that neither buildings nor existing rails are damaged, the consortium installed a measurement system with around 2,000 measurement units and well over 5,000 individual sensors that constantly deliver data on subsoil and building movements. Drilling for extensive elevation injections will begin in late 2022; these prevent the surrounding buildings from subsiding as a result of settling following the tunnelling. Another issue is dealing with ground water. More than 130 wells ensure that the water pressure on the surrounding diaphragm wall and tunnels does not become excessive. The water treatment plant to the south of the site prevents potential contamination from the site’s waste water from entering Munich’s water supply system.

Currently, the engineers are working to produce the first ceiling under the top ceiling (E-1), eight metres below ground. This involves joint venture 72-metre special crane, capable of lifting loads of up to 48 tonnes. This transports reinforcement rods through one of the openings on the level below, supported by just one member of the joint venture team in the burning July sun. The rest of the crew is enjoying more comfortable temperatures below ground.

Long-planned collaboration

The project would be a technical and logistical challenge. The joint venture partners therefore put a great deal of work into the very long bidding process, which went on for almost three years. This period brought them very close as a team, says Jens Classen. “The good thing about our joint venture is that a lot of people from both companies moved into the project directly from the bidding phase. That allowed us to use their expertise, and meant that we didn’t have to integrate a lot of new people into the team.”

Today, the Marienhof team benefits from the combined expertise of two major construction companies. Does tension ever arise? Jens Classen: “Not really. Despite all our experience, we are all learning all the time – including from one another. For example, we use HOCHTIEF’s SAP system for our invoice checking. In return, Implenia contributes the quality management system and the iTWO software solution for controlling.”

Making the partnership work demands a solid basis of trust and a conscious commitment to avoiding turf wars. After five years of collaboration, such conflicts are no longer an issue between the joint venture partners, says Michael Müller emphatically. “The good thing is that we can put all our expertise into the technology and the project – that is what makes construction fun.”

Home game in Munich

The motivation to help build the Marienhof is palpable throughout the team. “Many colleagues have moved to one of the companies to be part of this project,” says Classen. Especially veteran Munich tunnel builders were keen to be part of this project on their own doorstep. That is why many employees from both HOCHTIEF and Implenia are involved who have already had a lot of experience with large projects – and who now form the basis of this project.

At the same time, there are also many young people in the ranks of the Marienhofler. They learn in the slipstream of the experienced team, so to speak, how to successfully set up a large project – and they also get the chance to switch to another area again and again to gain new experience there. “In addition to their drive, the junior staff also bring along their know-how regarding digital working methods and thus complement us old hands,” Classen emphasises. “In this respect, it's a very pleasant mixture!”

Geglückter Know-how-Transfer

Like everywhere else in the construction industry, there is a lack of mid-level staff at Marienhof: for 20 years, only a few new people were hired. This makes it all the more important now to pass on the know-how of experienced colleagues to the next generation and thus keep them in the project. “Many of the older employees will retire during the project. That's why we deliberately paired experienced people with young people within the teams – the combination is almost unbeatable.”

Face-to-face discussion is also a major feature of the very friendly atmosphere in the construction office. Most people here do not even know for sure who joined the group from Implenia and who from HOCHTIEF. They are one team.