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Cologne tunnel collapse


Emergency workers were rushing to stabilise a rail tunnel in Cologne, Germany yesterday near to the site where a six-storey concrete building collapsed on Tuesday.

The tunnels for the north to south light rail project - known as nord-sud Stadtbahn Köln -ran alongside thecity's archive building, and are believed to be behind the collapse of the building which measured 50m by 70m on plan.

"Earth under the archive building slid into the tunnel of the subway, causing the building to collapse," said a police spokesman."The total building has collapsed, everything has gone including the two buildings to the left and right of it."

In an emergency procedure, firemen have been pumping 1,000m3 ofconcrete into the new tunnels for the majority of the day in a bid to stabilise the 50m length around where the failure had occurred.

"The groundwater tended to lift the tubes [tunnels]," said a Cologne city council spokesman. "Concrete is heavier [than the groundwater].Firemen put concrete in the tubes to stabilise them [and fill the voids]."

Two residents from a neighbouring building on the street of Severinstrasse are still missing, but rescue teams are unable to get into the centre of the site until the tunnels are filled with concrete and the damaged buildings either side of the archive building pulled down.

A statement from the Cologne Transportation Authorities (KVB) said that: "Irrespective of the cause, we express our deepest
regret to those affected and for their injuries, damages and anxieties." KVB added that its priority was finding the missing people but that an investigation into the cause of the collapse would start as soon as possible.

The tunnelling works in this area for the north to south light rail project had been completed about three years ago, according to a spokesmanfor Bilfinger Berger, one of the three contractors who make up the contractor joint venture for the project. The other two contractors are Wayff and Freytag and Züblin.

Atunnel boring machine formed the tunnel whichwas then lined with precast concrete rings, about 28m below ground level. A spokesman for Bilfinger Bergen and Züblinrefused to be drawn on the cause of the collapse and said aninvestigation is being carried out.

Acut and cover crossover point for the trams is also beingbuilt in theWaidmarkt area, comprising diaphragm walls and a concrete slab roof.

"Cracks were reported for the first time in 2007," said the council spokesman. "These were supervised by specialists who said that there was no problem for stability. There was a second examination in 2008 by another specialist who also said there was no danger."

The noise of the building giving way on Tuesday was noticed by the staff around five minutes before the building collapsed allowing staff time to escape.