Hallandsås celebrates first tunnel finish
Aug 2010
Shani Wallis, TunnelTalk
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First tube through at last!
- A full diameter rail tunnel now pierces the Hallandsås ridge in Sweden. On Wednesday this week (Aug 25, 2010), the one 10.6m diameter Herrenknecht TBM working on the twin tube railway tunnel project broke through into a 1.5km reach of drill+blast excavation completed under a previous contract.
- The breakthrough closes out nearly four and a half years of continuous round-the-clock work to complete the 5km of segmentally-lined, TBM tunnel between the 1.5km and 2km of drill+blast work from the north and south portals respectively. The TBM will now be dismantled and withdrawn from its in-tunnel breakthrough, and returned to the face of the south portal drill+blast heading to repeat the process for the parallel tube.
- "This is a great day for everyone working on the project and a major step towards eliminating the greatest bottleneck on the West Coast Line," said Per Rydberg, Project Director at the Swedish Transport Administration on the occasion of the celebrations.
- The twin tube, double track rail tunnel has been under construction since the early 1990s and has overcome serious geological, political, technical and environmental setbacks. Even operation of the Herrenknecht TBM procured for this successful attempt at one of the most geotechnically difficult projects of all time has had to undergo changes. Designed to operate as a slurry Mixshield and withstand hydrostatic pressures of up to 15 bar, the method was changed to open mode TBM excavation with extensive pre-excavation grouting to control the high volume, high pressure ground water conditions.
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Per Rydberg, Project Director, Trafikverket
- Through the 250-300m long Mölleback Zone (MBZ) of the 8.6km long tunnel, neither technique was considered capable of success and instead the entire zone was pre-supported with a ground freezing operation. Specially designed glass fibre freeze pipes were installed horizontally from within a pilot tunnel driven from the north drill+blast face to establish the freeze well ahead of the TBM heading from the south. The machine intersected the freeze zone in mid-May 2010 and it took 14 days to drive through the frozen zone, cutting through the glass-fibre feeze pipes as it advanced. For the last 600m the 10.8m diameter TBM has excavated the collar of rock that surrounds the central smaller diameter pilot, breaking through on Wednesday into the completed drill+blast heading.
- Completing the HallandsÅs rail tunnel, no matter its technical challenges and financial costs, is vital to the operation of rail services in Sweden. The country's important West Coast Line is currently 85% double track. The sharp curves on the single track over the Hallandsås ridge constitute a serious bottleneck. When the double track through Hallandsås is completed, a doubling of rail freight tonnage will be possible, and the number of trains per day can increase from the current number of four to 24 per hour. A double track railway is said to correspond to a 16-lane highway in capacity.
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Frozen pilot through the MBZ
- The first trains are expected to pass through Hallandsåsen in 2015. "We have a well-functioning method and have gained valuable experience that we bring with us for completing the twin TBM drive," says Anders Rehnström, Project Director for the project's construction joint venture Skanska-Vinci.
- The first TBM hole through is achieved ahead of the anticipated mid-September 2010 date and the second drive can be expected to come in earlier than programmed as well. The worst of the unknown is now largely behind them.
- Hallandsås through the freeze zone - TunnelTalk, June 2010
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