Commissioned by the Swedish Transport Administration, Skanska - Vinci HB has been tasked with completing the rail tunnel through the Hallandsås ridge, from Förslöv in the south to Båstad in the north.
The project consists of two 8.7-kilometer parallel single-track tunnels. Some 19 cross-passage tunnels will also be constructed connecting the two main tunnels. The tunnel will be inaugurated in 2015, but our part of the project will be completed in 2014.
The best TBM, the best self-inspection and environmental program and the best finances – three major reasons as to why Skanska-Vinci was awarded the contract to complete the tunnel through the Hallandsås ridge.
The Skanska-Vinci HB consortium will build the tunnel as part of a design-construct contract, meaning that Skanska-Vinci is responsible for design, planning and construction of the project.
The geological conditions at the Hallandsås ridge present a substantial challenge. The ridge was created as a result of enormous forces millions of years ago. The geology is highly varied and different compared with the conditions commonly found in Sweden.
In places, the bedrock is fractured and thus contains much water. Unlike many other tunnel projects around the world, we are not allowed to drain away substantial volumes of water from the ridge.
To protect the nature of the Hallandsås area, the project is subject to an environmental permit. The project is adapted to comply with all the conditions of this permit and the technical solutions for the tunnel construction have been adjusted to these conditions and circumstances.
The TBM named Åsa is being used to bore the tunnel through the Hallandsås ridge. The 250-meter-long machine is specially adapted to the difficult geological conditions at the ridge. The person who operates the TBM is known as the pilot and sits in a control room on the TBM from where he controls all of the machine’s systems.
The TBM builds a watertight tube of concrete segments behind it. The method is known as lining and is used to prevent groundwater from entering the tunnel. The plant that manufactures the concrete segments is situated in Åstorp, about 30 kilometers from Förslöv.
Almost 400 people from throughout Europe work on the project. In addition to the TBM worksite, they are stationed in three locations: the Southern site, the Northern site and the segment plant in Åstorp.
Largest work site: Southern site
The Southern site is the largest work site and all logistics serving the TBM are based at the south end. A large water treatment plant is located at the mouth of the tunnel in addition to a concrete batching plant, workshop, electrical workshop and a large crane for unloading the concrete segments that arrive by train from Åstorp. We have even built our own railway to transport personnel and material in and out of the tunnel. The broken rock is removed from the tunnel on a conveyer belt system.
The southern entrance also has two assembly halls located about 1,800 meters into the ridge. The TBM was assembled in the eastern chamber before it commenced work. When the TBM will start work on the western tunnel, it will be assembled in the western chamber.
Conventional tunneling methods at the Northern site
Conventional tunneling work is being carried out at the Northern site. Here, we blasted a reception chamber some 1,700 meters into the ridge; a point that was reached by the TBM Åsa on August 25, 2010. The chamber was necessary since the cutter head is bigger than the finished tunnel and must therefore be dismantled. The rest of the machine is subsequently pulled back through the tunnel and prepared to commence boring the western tunnel tube through the Hallandsås ridge. Valuable lessons concerning the geological conditions were learned from Åsa’s first journey through the ridge.
The Northern site is also responsible for preliminary treatment of the Mölleback zone – a 300-meter-long area of fractured rock.
Gigantic chest freezer
The quality of the rock in the Mölleback zone is intermittently poor. The rock is fractured, porous and contains substantial volumes of water, thus presenting major challenges for the tunnel project. To stabilize the rock, remove water and facilitate boring, a gigantic chest freezer has been created in the area.
When the area freezes, the water and rock in the area combine into an ice mass. In addition, cement is used to reinforce part of the rock. Roughly the same principal as that for cooling an ice rink is used to freeze the rock. A number of horizontal pipes are drilled into the area to be frozen through which coolant is circulated at about minus 40 degrees Celsius in a closed system.
Working 24 hours a day
Work on the tunnel never stops. The team of 20 people who work on the TBM start at 7 a.m. Twelve hours later, they are relieved by the next shift, who work throughout the night until seven the next morning. The change-over of shifts takes place in the ridge.
A shift consists of several different duties and work locations. Some of the team work in the area outside the tunnel and plan material transportation into the TBM. Others work in the water treatment plant, the concrete batching plant or in the workshop performing service.
There are a number of different jobs on the TBM. The TBM pilot steers the TBM while others are responsible for positioning the concrete sections that form the tunnel and so on. Some personnel have specialist areas and others have multiple tasks; when needed, personnel switch between assignments to assist each other.
Safety at the top of the agenda
Working with a TBM is special because of the inward and outward transportation of goods and because of the very limited space in and around the machine. Those who work here must lift, carry and perform many other duties in a very restricted area. They are also required to crawl into the cutter head to replace disk cutters.
Working conditions are prioritized, and because this is Skanska’s largest project in Sweden, there are more personnel than usual actively working on these issues. We work in a preventative manner and conduct safety rounds where accident risks are reported.
Safety during tunnel construction is paramount. During the project, refuge chambers are located at various locations in the tunnel and equipped with enough oxygen to facilitate survival for up to 20 hours. One of these chambers is a so-called mobile refuge chamber, enabling it to travel on the rails.
The project in figures
• About 400 people are working on the project
• 200,000 cubic meters of concrete are needed to construct the 40,000 concrete segments
• About 40,000 concrete segments have been produced, each weighing 12 tons
• With a diameter of 5.6 meters, the ball bearing in the cutter head is one of the world’s largest
• The TBM is 250 meters long and weighs 3,200 tons
• 23 cubic meters of saline solution is used as coolant to freeze the Mölleback zone