Tunnel vision

The Challenge

Twenty meters beneath the streets of Malmö, Sweden, the new underground section of the city’s central station is gradually taking shape. Currently cavernous and empty, with music from workmen’s radios echoing off the walls and the smell of concrete dust in the air, it will in December next year be a major transport hub connecting Sweden’s third city with Denmark’s largest, Copenhagen.

Malmö Citytunnel Group, the consortium behind the project, has demanded that the concrete in the tunnel lasts 120 years – as must everything mounted in it, such as the gantry carrying electric cables, water pipes and ventilation pipes that run the length of the 350m-long platform. Contractor NCC, responsible for the underground station and platform, was tasked with finding a solution that would keep the gantry firmly bolted to the tunnel’s roof and able to resist the pressure waves created by trains entering and leaving the station.

The Solution

The answer was a series of steel rails cast into the concrete of the tunnel roof. Into these rails are secured thousands of anchor bolts manufactured by Halfen-Deha in top-quality A5 steel, each of which is secured with a Nord-Lock washer pair.

“We insert each anchor bolt into the rail, twist it 90 degrees, and then tighten it,” says Jörgen Andersson, site engineer with NCC. “This is supposed to hold for a very long time, so the demands on the bolts and the washers are very high. We are counting on them to do a good job.”

The Result

While there is much to be done before the first train pulls in – the Citytunnel is currently six months ahead of schedule – the gantry project is finished. There are 5,000 anchor bolts, painted with white fire-resistant paint, holding the gantry solidly in place in preparation for the buffeting created by the arrival of dozens of trains a day passing through Malmö Central Station along the €1 bn Citytunnel line. At €5 a piece for more than a century of service, the lifecycle cost is minimal.

“We are pleased with the result. No problems at all,” says ­Andersson. “With the Citytunnel it would be very difficult to do repairs or maintenance if something went wrong because it is out of the question to close the tunnel to get access. But they won’t have to worry about this gantry for another 120 years.”