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Copenhagen subway extension work delayed after Cologne collapse

Plans for an extension to Copenhagen’s subway have been delayed following the Cologne collapse that killed two people earlier this month.

Danish politicians have demanded assurances that the proposed construction method is safe after a six storey building in Cologne collapsed into an underground excavation for a new subway.

“The final decision on where the stations and tunnels should be has been delayed by one week,” said a spokesman for the Copenhagen metro.

“The parliamentary committee are asking more questions to make sure the construction work is ok and safe.”

The construction methods for the two projects are similar as in Copenhagen it is vital to prevent lowering of the groundwater table.

A lowered water table could cause the surrounding buildings to settle.   In some parts of Copenhagen, building foundations were constructed using wooden piles that are under water. A lowering of the water table would expose these foundations to air, and at worst they would disintegrate in a few years as the result of fungal attack.

The construction method to be used must prevent this groundwater lowering and to monitor groundwater levels, a number of boreholes have been drilled along the entire Metro. The groundwater level in these holes is continuously checked.

Boring began in August 2007 and in total around 350 individual geotechnical holes have been driven.     Data from the geotechnical investigations will be used to calculate how much earth pressure tunnels, stations and shafts can withstand.         

Pumping tests from the water-bearing strata in the subsoil will show where the water-bearing layers are located and how far away the effect of the construction work can be traced. This helps to prevent damage to buildings in the area.

Tunnel stations are built from the top down, as in Cologne. Concrete secant piles are used to form a cohesive watertight wall.

The fourth phase of the Metro is expected to open in 2018. The new line will have 17 stations and will cover major parts of the city centre as well as the Østerbro, Nørrebro, and Vesterbro districts and the Municipality of Frederiksberg currently not covered by commuter rail or Metro line services.

The first phase of the Copenhagen Metro was opened in 2002 and 2003. Back then the two Metro lines ran from Vanløse to Vestamager and Lergravsparken.

The third phase opened in September 2007 as an extension of the existing line which until then terminated at Lergravsparken station. The completion of the third phase means passengers can now take the Metro all the way to Copenhagen Airport in Kastrup. A trip from the City centre of Copenhagen to the airport takes only 14 minutes.

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