Construction Journal

July 10, 2019

The ice age is over!

U-Bahnhof Museumsinsel, Juli 2019, Innenschale betoniert © A. Reetz-Graudenz

The next major step in the shell construction of the Museum Island underground station has been completed: concreting of the inner shells in the later track areas was completed on schedule. Under our management, the German northeast branch of the Swiss construction and construction services company Implenia carried out the construction work: In continuous 24-hour operation within less than four months, two tunnels, each 105 meters long, were concreted. An outstanding performance by the engineers and construction workers on site!

The ground ice that had previously been necessary for construction to protect against groundwater can now be thawed in a controlled manner. This ends the largest inner-city ground freezing in Europe to date.

The 28,000 cubic metres of frozen ground was frozen from February to May 2018 by pumping a potassium chloride solution at a temperature of -37°C through almost 70 icing lances, each 105 metres long, in the ground in a closed cooling circuit. In this way, heat was extracted from the ground and the frozen body was built up to the intended thickness. Throughout the entire operation, the composition of the frost body was closely monitored over thousands of temperature measurement points. Now the ice body is thawed in a controlled manner in order to maintain the full water pressure on the now concreted inner shell during the carcass construction.

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