On Dec. 8, Sweden’s longest tunnel – the 8.7-km Hallandsås Tunnel – held an inauguration ceremony attended by Minister of Finance Mikael Damberg, Båstad Mayor Bo Wendt, Governor of Skåne Margareta Palsson, Swedish Transport Administration Director General Lena Erixson, and Project Manager Botond Orban.
The inauguration completes a long history of the project. Construction of the tunnel through the Hallandsås Ridge began in 1992. The Kraftbyggarna contracting company started the project using an open tunnel boring machine, a technique that proved faulty soon after work began. The tunnel boring machine, known as “Hallborr”, was designed for construction in hard rock. The rock in Hallandsås is partly cracked and disintegrated and contains a large amount of water. Kraftbyggarna was forced early on to abandon boring using Hallborr. In 1993, Kraftbyggarna instead began construction using the more conventional technique of excavating and blasting their way forward. Kraftbyggarna completed approximately 3 km of tunnel before leaving the project in 1995.
Skanska took over as the contractor for the project in 1996 and continued excavating and blasting the tunnel. To make up for the time lost by Kraftbyggarna, Skanska opened an adit in the centre of the ridge, known as the Mid Adit. This provided the company with more fronts from which to work. In summer 1996, large quantities of water leaked into the northern tunnel, causing the groundwater to drop and wells in Hallandsås to dry out. To stop the leak, some 80 cement-based sealing products were tested, but none of the products were able to penetrate the finest cracks to seal the tunnel.
Several experts participated in an evaluation that resulted in the project testing the chemical sealant Rhoca Gil, a product that had a long history of international use. In 1997, use of the product was discontinued after it was discovered that parts of the sealant had not hardened due to the heavy water flow and high water pressure in Hallandsås, causing the water in the streams into which the tunnel water was released to be contaminated with acrylamide. Fish began to die and cattle that drank from the streams became sick; the leak caused major concerns among the residents in Båstad Municipality.
Tunnel construction stopped in 1997 Trafikverket (formerly known as Banverket) and Skanska discontinued construction of the tunnel upon learning of the acrylamide leak. A risk zone was set up around the tunnels and animals were put down and crops were destroyed as a precaution. When the tunnel construction was discontinued, one third of the tunnel had been completed.
An extensive investigation was launched to look into the measures that need to be taken to restore the environment. In cooperation with the Swedish Government, Trafikverket and Skanska appointed a claims settlement group that quickly processed the compensation claims of the individuals affected. The Government also appointed a commission to investigate the cause of the accident.
In the years following the acrylamide accident, Trafikverket and Skanska invested extensive resources in decontamination, sealing and environmental work. The areas with the worst leaks were sealed using concrete pipes that were cast in place, known as linings. The acrylamide was decontaminated whenever possible and the ridge was given a clean bill of health.
Between 1998 and 2000, Trafikverket, at the request of the Swedish Government, investigated the possible technology, environmental effects and costs involved in continuing the construction of the tunnel. The investigations showed that continuing the construction of the tunnel would affect the groundwater so it was necessary to seal the tunnels with a water proof lining and use a shielded tunnel-boring machine. Another important lesson learned after the troubles in the 1990s was that the environmental controls and information would need to play a central roles in the continued construction.
In 2001, the Swedish Riksdag and Government gave the green light to continuing building the tunnel. In 2002, the Skanska-Vinci consortium was contracted to continue construction. In 2003, the project was granted a building permit from Båstad Municipality and the Environmental High Court granted a permit to allow 100 liters per second inleakage during the construction period. Preparations to resume the construction of the tunnel began.
Skanska and Vinci started tunneling on the first Eastern tunnel in September 2005. Tunneling teams and engineers approached the optimum working method in the tunnel in close and trusting cooperation of machine supplier and construction companies. The best results were obtained with the machine named “Åsa” in the open mode with cement injections that kept the groundwater at bay. High abrasivity and blocky rock on parts of the route caused an extremely high wear of material at the cutterhead, and the maintenance and tool change intervals were correspondingly high. However, soon after the start of tunneling, jobsite reports showed regular progress, although time-consuming cement grouting and the required service intervals meant limited speed. Nevertheless, man and machine were able to force some hundred meters of tunnel per month from the mountain.
Then, spring 2008 saw the first victory of many with the breakthrough into the cavern of a mid adit, which had been excavated with conventional methods. On that occasion, the highly worn cutterhead was replaced by a new one with larger disc cutters (19 in. instead of 17 in.). Finally, in August 2010 the entire first tunnel was successfully completed. The machine was completely refurbished and again equipped with a new cutterhead for excavating the second western tunnel. Herrenknecht field service rendered active assistance on the jobsite with staff and the supply of spare and wear parts: they assisted in the assembly of the machine on the jobsite, during tunneling in both tunnels and in the restructuring and refurbishment work for the second drive.
From February 2011 onward, specialists from the Skanska-Vinci joint venture drove the machine from Förslöv toward Båstad for the second tunnel, where they were welcomed and celebrated by a large and festive party at final breakthrough on Sept. 4, 2013. Dr.-Ing. E.h. Martin Herrenknecht was present to attend this event: “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.”
After almost 8 years of tunneling, this finish marked an outstandingly pioneering achievement in the construction of underground infrastructure. Thanks to state-of-the-art tunneling technology and trusting cooperation of all project partners, even a tunnel project that seemed to be impossible could be managed safely for people and the environment.