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Frankfurt, central railway station

Jet grouting site facilities in front of the railway station.
Facts and Figures
Company Stump-Franki Spezialtiefbau GmbH
PrincipalFranz Kassecker GmbH, Waldsassen
LocationFrankfurt - Germany
Type Specialist civil engineering
Runtime01.2019 - 12.2021

Jet-grouted underpinnings and floor slab for a 400m cable duct tunnel.

Official fire protection standards required the refurbishment of the electrotechnical equipment in a new cable shaft tunnel of the Frankfurt central railway station.

A 400m tunnel under the railway station

Two new floor ducts were constructed at depths of up to 2.6m for the project. The tunnels had a total combined length of around 400m. As the foundations of the adjacent holdings did not extend far enough into the earth for the new construction, underpinnings to the foundations had to be installed on both sides along the full length of the completed tunnel with jet grouting. Owing to the roof construction of the railway station, heavily loaded individual foundations had to be underpinned with as little settlement as possible.
In places, jet grouted floor slabs had to be manufactured in the soil to provide reciprocal buttressing for the underpinning body. The practice of stump jetting, introduced by the building authorities, was used for this project.

Complex construction site logistics

Electrically driven machines were only able to reach the ground surface after 400m. Only excellent and very close collaboration between all companies involved with the site made it possible to overcome the complex logistics of this project.
The extremely limited space, the aged buildings and the lack of inventory documents for the railway station meant works had to be regularly and quickly adapted to the actual geometric situation.

Technical data / quantities

Cubage of jet grouting

1,415m³ contracted,
approx. 3,000m³ actually used in execution

Unit diameter

up to 1.2m

Drilling depth/jet length

up to 8m/up to 6m