Herrenknecht wins Hallandsås

1 March 2003

Herrenknecht will supply the TBM that will be used to finish construction of the controversial 8km long Hallandsås rail tunnel. The project, halted six years ago for environmental reasons, will call for a dual mode machine to work in hard rock and incredible pressures of up to 13 bar.

The Environmental Court in Växkö, Sweden, gave the go-ahead last month for the tunnel's completion. The judgement was granted partly on the basis that the contractor, Skanska/Vinci, would use a TBM to bore the twin tunnels, instead of drill and blast (T&TI, December 2002, p10).

Tunnelling was suspended in 1997 when the grout used, polluted the water table and affected the project's miners. The contractor, Skanska, was fined US$300,000 for it's part in the disaster.

The Environmental Court will also permit a tripling of water extraction, allowing a maximum of 100 litres/second on average per month to be channelled away during the construction of the tunnel.

"This was the point on which the construction of the tunnel hinged," Christer Möller, project manager for the client, Banverket, said. Strict conditions accompany the decision, including method of water extraction, and risk control and management.

A TBM with the option of working in closed-face mode, was the only method available to ensure that the permitted levels of water extraction were not exceeded. Where drill and blast opens long sections of tunnel before waterproofing is possible, TBMs can erect a watertight concrete lining behind the head.

"If we are in danger of exceeding the monthly average, we can change to closed-face mode," Simon Taylor, TBM supervisor for the client, said. However, the pressure at the face is expected to reach 13 bar. "Very few projects have had TBMs that operated in closed-face mode in those sorts of pressures. Our intention, though, is to mine in open mode," Taylor said.

The Hallandsås will be Sweden's first tunnel constructed by TBM. "There are very few reference points we can use and this is also uncharted territory for the TBM manufacturer," Taylor said.

The closest recent comparison in term of pressure is Holland's Westerschelde tunnel, completed in March 2002. There, engineers worked in up to 6 bar of pressure. T&TI understands that Herrenknecht will design and build a 10.5m diameter TBM to bore both tubes of the Hallandsås tunnel.

Båstad Municipality is expected to give the green light for construction this month. The TBM will not be ready until 2005, and the scheduled completion date is 2011.