The concrete bolt that keeps thousands moving: TOGE Dübel and Nord-Lock strengthen Nuremberg’s metro

The people of Nuremberg are proud of their underground system, a pioneering network which is among the most modern in Europe. The city, located in Bavaria, southern Germany, has the only underground system in the country where two of the three lines operate automatically. For almost two decades these lines have been running entirely without drivers, carrying more than 200,000 people around the city during working days. To do so without delay or disruption, every detail of the metro’s infrastructure must be carefully maintained – from the rolling stock down to the bolts holding its concrete structures together.

After 40 years of continuous use, a renovation of the metro system’s track beds was required to ensure passenger safety and efficient operations. The main beams which bolt the tracks to the tunnel floor, known as a concrete stringer, had sustained too much wear and tear damage in too many places to continue being used without intervention.

That was no small issue for the provider of the Nuremberg metro service, VAG (Verkehrs-Aktiengesellschaft Nürnberg). Normally, metro companies need to completely shut down a track for weeks to renovate concrete stringers using traditional methods. Employing water pressure to remove the concrete is a time-consuming and ­– considering the many power lines inside the tunnel – extremely dangerous job.

Long delays caused by closed tunnels are also costly for the operators, adversely affecting train traffic and irritating passengers. But what if there was a more effective solution? That’s where TOGE Dübel, supported by Nord-Lock X-series washers, stepped in.

Minimizing disruption and maximizing stability: more than just a concrete bolt

A brand-new solution caught VAG’s attention just as they started planning the project. Local Nuremberg dowel and concrete bolt manufacturer TOGE Dübel won a railway innovation award for a concept they originally developed to enhance the structural sustainability of bridges. VAG representatives present in the audience were intrigued and had the idea of utilizing the concept in an underground rail environment for the first time. Could it also be used to strengthen the structure of existing concrete stringers?

Indeed it could. Initial work began at three metro stations: Bärenschanze, Gostenhof and Maximilianstrasse. The project soon expanded to the second largest station in the network, the “Plärrer”, with the unique concrete bolting method used to carry out renovations there at night-time, minimizing disruption of the busy station which traffics 98,000 passengers daily.

Instead of completely reconstructing the stringers, in the new method, concrete bolts measuring 36 centimetres and weighing one kilo are utilised as load-bearing components to improve the life span of the overall track bed construction. The bolts are fitted with a patented special thread that cuts into the borehole wall upon application. The force of the bolts is mechanically transferred to the anchor base, and the concrete is fixed in place. Nord-Lock X-series washers are used to secure the concrete bolts, providing additional stability.

“Completely removing a concrete stringer and installing a new one could never be accomplished without service disruption,” explained Waldemar Gunkel, Technical Director of TOGE and one of the two inventors of the new generation of concrete bolts.

“In Nuremberg, however, our system is only installed between the hours of 23.00 and 04.00. By the morning, everything runs normally.”

Nord-Lock’s journey from Deutsche Bahn to the Nuremberg U-bahn

During these working hours, only one track was shut down, with trains redirected via a single track while the porous areas of concrete on each stringer were chipped away and replaced. Finally, the stringers are fixed into the ground, utilising the concrete bolts.

Since the bolts need to be drilled into the concrete and the drilling machine might not be positioned at an exact 90-degree angle, the risk of inclination needed to be addressed. For that reason, all concrete bolts used were secured by Nord-Lock X-series washers. Their conical shape compensates for the inclination, while the wedge effect prevents spontaneous bolt loosening due to vibration.

The Nord-Lock connection came via Deutsche Bahn – Germany’s national railway operator – who have long used Nord-Lock original wedge-locking technology as standard in their projects.

Jochen Süssenbach, the account project manager at Nord-Lock, said there is great potential in this innovative method of metro renovation:

“We’re looking at a huge renovation of tunnels yet one that virtually doesn’t affect the timetable. In terms of costs it’s also a solution that beats any conventional method”.

Proof of the efficiency of this method came when the first construction phase was completed a week ahead of schedule. The total time for construction at the first three metro stations was a matter of weeks, rather than several months as would have been the case with the previous method.

Concrete bolts designed to last, for a network that needs to last

The concrete bolts are designed to last for 50 years. While concrete itself cannot last that long, further renovations will not be needed for decades.

Describing TOGE’s award-winning solution, Bavarian Interior and Transport Minister Joachim Herrmann said “we have our fingers right on the pulse”, alluding to the need to address the poor condition of some of Germany’s infrastructure, including highways and railway bridges, as well as underground rail systems which were largely established in the 1970s.

TOGE’s Gunkel meanwhile summed up the project as proof that their concrete bolting solution found an important application: “This project gives us the boost to further drive our product development forward”.

KEY TAKEAWAYS

Use case:
Concrete bolting solution harnessing Nord-Lock X-series washers

Client:
TOGE Dübel GmbH & Co.KG for end customer Verkehrs-Aktiengesellschaft Nürnberg (VAG)

Location:
Nuremberg, Germany

Benefits gained:• Reinforced existing concrete without the need to replace the entire structure
• Minimized impact on metro traffic uptime through efficiency of installation
• Reliability across multiple environments
• Safety under dynamic load vibrations caused by trains
• Strong partnership to innovate and solve problems quickly