Construction Journal

Dec. 2, 2019

The Alex-Tunnel loses weight

Verfüllung mit Schaumglasschotter Alex-Tunnel November 2019 © A. Reetz-Graudenz

The underground stations Alexanderplatz and Rotes Rathaus are connected by a 90 year old tunnel, the so-called Alex Tunnel. The tunnel was renovated from May 2016 to April 2019. During excavation work there in 2017, it was noticed that the tunnel is covered with more massive layers of soil than indicated in the plans. In order for the U5 to be able to pass through there safely in just over a year, the load over the tunnel must be reduced by 10,000 tonnes. In this so-called "lightening", the heavy soil layers are removed and filled with foam glass gravel. This material has the advantage that it is particularly light on the one hand and on the other hand it can withstand a later tram crossing.

Since the middle of September, the "lightening" has been running in front of the Rathauspassagen / Rathausstraße 5 over the Waisentunnel / Alex-Tunnel junction. The whole area in front of the Rathauspassagen has been excavated in the meantime. Since last Thursday the excavation pit is filled up with foam glass gravel.

The challenge of the "lightening" is mainly the coordination with the pipe carriers, who have to move numerous pipes and cables in the areas before our construction work can be done.

From January 2020, the "lightening" will begin along the entire length of the Alex Tunnel. This means that the construction fence will extend along Rathausstrasse from the container castle to Gontardstrasse. It will be gradually dismantled from the east.

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