Denmark is to have its first bored tunnel using steel fibre reinforced concrete elements instead of the traditional steel bar reinforcement. The steel fibre reinforced concrete will be used as liner in a district heating tunnel intended to last 100 years.
It looks exactly like a haystack, although the cows’ stomachs would churn if they tried to eat this entangled mass. But if you separate the ‘needles’ in the haystack, mix them with sand, water, stone and cement and mould them into a sort of baking tray, you end up with an extremely robust product far removed from the plant world.
For this product is a mixture of concrete and steel fibres, and soon it is to be put to the test as building material in a 4 km long district heating tunnel 4.8 metres in diameter deep underground beneath central Copenhagen.
This is the first time in Denmark that a bored tunnel is to be built using steel fibre reinforced elements. The elements are rhomboid, rectangular, curved concrete slabs that will form the inner lining of the tunnel. Concrete elements with steel reinforcement would normally be used for bored tunnels, but there are numerous benefits to using steel fibres measuring no more than 47 mm in length and 0.8 mm in diameter.
”First and foremost, these tiny steel fibres save society massive amounts of money,” claims COWI’s project team: project manager Morten Faurschou, Carola Edvardsen, Thomas Kasper and Jens Nymann. “They are cheaper to produce than steel bars and do not rust – the cause of concrete spalling - which also means reduced repair costs.
Also, traditional reinforced concrete gets more easily damaged at the edges and corners during transportation and actual construction. In their finished state, most bored tunnels can last without traditional reinforcement. Steel fibre reinforced concrete can be considered the optimal material for the district heating tunnel. The tunnel we are now building should last 100 years.”
COWI, which is designing and supervising the tunnel construction for Copenhagen Energy, is the first consultant in Scandinavia to use the steel fibre reinforced tunnel elements. They have only been used twice before: in a test section of a tunnel in the Netherlands in 1998 and in a tunnel project in England in 2002-2003.
The tunnel in England is shorter than the district heating tunnel in Copenhagen, but the experience has been so positive that the people of Copenhagen will soon have the new building material in use beneath their feet. The tunnel will be built between 25 and 41 metres deep in the earth, in a line from Amagerværket south of Copenhagen city centre to Adelgade in Copenhagen, where it will turn and continue to the Nørrebro quarter on the north side of the city. If the full potential of the material is realised, it will certainly make an obvious choice for the next stage of Copenhagen’s metro expansion.
By Eva Isager, cht@cowi.comPulished: 24.3.2006
Work begins in May on boring a 4 km long district heating tunnel beneath the centre of Copenhagen. The tunnel will be lined with steel fibre reinforced elements instead of the more traditional reinforced iron elements. This will make the project cheaper and the tunnel more durable. COWI is the first consultant in Scandinavia to use the new building material for tunnel elements.
Morten FaurschouProject managermnf@cowi.com