Patrick Reynolds for TunnelTalk
- The final TBM breakthrough on the Hallandsås rail tunnel project in Sweden took place today (Wednesday 4 Sept 2013).
Understated event ends all main tunnel excavation
- Boring on the 8.6km long twin-tube link through a ridge of geological material with a high groundwater content, involved major operations of a closed slurry mode TBM, pre-consolidation pre-grouting, and an extensive ground freezing installation. The single, 10.6m o.d. Herrenknecht TBM on the project, cleared the 250-300m frozen section through the Mölleback Zone (MBZ) for the final time in late June.
- Following a short maintenance stop, the JV contractor Vinci and Skanska had the shield underway again in early July. During the maintenance period it was judged that final breakthrough might happen in September or October but good progress on the final section of the drive northward enabled the TBM to finish this week, at the start of September.
- After eight long years, and tackling some of the most complex geology possible, completion of the TBM drive through the previously impenetrable Hallandsås mountain range south of Båstad in Sweden marks a major achievement for the project owner, Trafikverket (the Swedish Transport Administration), the contractor joint venture of Skanska/Vinci, and the machine manufacturer Herrenknecht.
Fig 1. Pre-grouting and ground freezing through the MBZ
- "We have shown that it is possible to build a tunnel of high quality through the complicated Hallandsås, while at the same time meeting the high environmental requirements. Our competent and dedicated co-workers are today worthy of every recognition they receive for completing this huge achievement," said Per Rydberg, project manager of Trafikverket at the breakthrough ceremony.
- Large sections of the highly abrasive rock formations (mainly gneiss and amphibolite), with high rock strengths of up to 250MPa, proved to be extremely fissured. Additionally, the tunnel was exposed to extreme groundwater pressures of more than 10bar for long stretches of the route. Earlier attempts to overcome these barriers failed, and mechanized tunnelling was the final solution.
- Herrenknecht developed and delivered a specially adapted TBM for the two remaining 5.5km twin running sections of the overall 8.7km long tunnels. The machine was specially designed to work in both the closed slurry mode, with hydraulic removal of muck, and in the open hard rock mode with conveyor belt removal of excavated material. Permanently installed drilling and injection tools ensured water inflow could be controlled by grout injection when needed. The sealing system was designed to withstand groundwater pressures of up to 13 bar. "The machine design for Hallandsås was both a response to the extreme project requirements and the need to meet technological challenges," said Werner Burger, Head of Design Department Traffic Tunnelling at Herrenknecht. "The concept aimed to provide a hard rock machine with the potential to work safely and efficiently in loose rock, but also under high groundwater pressure if needed. Hallandsås has set the standard for future projects," he added.
Working site of the twin 8.6km long rail tunnel
View of the rail tunnel pass through the ridge
- Best results were achieved in open mode with injected cement to keep the groundwater at bay. High abrasivity and blocky rock on parts of the route caused extremely high wear at the cutterhead, and maintenance and tool change intervals were correspondingly high. However, soon after the start of tunnelling, jobsite reports showed regular progress, although time-consuming cement grouting and frequent maintenance shutdowns meant limited speed.
- Spring 2008 saw the first breakthrough into a mid-adit cavern that had been excavated using conventional methods. It was here that the highly worn cutterhead was replaced and larger 19in disc cutters installed. By August 2010 the first tunnel had been successfully completed.
- The machine was then completely refurbished, and again equipped with a new cutterhead for excavation of the second western tunnel. Herrenknecht Field Service staff supported the contractor JV during the entire operation and maintenance programme.
- "This breakthrough is an absolutely great moment in my life. A big success for all those involved. It is like the moon landing of tunnel construction. Nobody else has been here before us," said Martin Herrenknecht, who was present at final breakthrough on 4 September 2013. "Thanks to state-of-the-art tunnelling technology and high levels of co-operation between all project partners even a tunnel project that once seemed impossible could be safely completed," he added.
Herrenknecht News Release
- Tunnelling on the project began in late 2005 and after significant troubles in the early stages, excavation by the Herrenknecht TBM started in early 2006. Breakthrough on the first tube was achieved in August 2010, some four and a half years after machine launch. TBM excavation of the second 8.6km long drive started in early 2011 and made predictably better progress towards this week's final breakthrough some two and a half years later.
- The geology along the alignment is highly abrasive but fractured and with a high water content, which had the TBM advance in both closed slurry mode as well as in open mode following pre-excavation grouting. The highly tectonically faulted Molleback Zone of variable and altered rock with a high ground water content required ground freezing for successful passage of the TBM and construction of the TBM (Fig 1).
- With some cross passage excavation still remaining to be completed, equipment installation on the project has commenced. The fit-out schedule for the main tunnels is expected to enable the rail link to come into service in 2015.
- Per Rydberg, Project Director for the Swedish Transport Administration, Trafikverket, said at the breakthrough: "Today we have taken the decisive step towards eliminating the single most difficult railway bottle-neck on the West Coast Line."
Hallandsås milestone achievement - TunnelTalk, June 2010
Hallandsås celebrates first tunnel finish - TunnelTalk, August 2010
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