Chewing through the Swiss Alps
Switzerland’s famous alpine mountains present a formidable obstacle to Europe’s increasingly fast and complicated transport network, but not for much longer. The world’s longest tunnel project and Europe’s biggest construction site can be found under the Swiss Alps.
Switzerland has to cope with an increasing number of trucks passing daily between Germany and Italy through the old alpine Gotthard route. This is in addition to the 150 trains that pass through the 130-year-old, 16 kilometre Gotthard railroad tunnel every day. The alpine route handles 20 million tonnes of freight every year, and this amount is forecast to reach more than 40 million tonnes in the next 20 years.
In the 1990s, the Swiss government embarked on a project to transfer passengers and freight from road to rail through a massive construction programme worth some 30 billion Swiss Francs ($40 billion). Almost half of this money is being spent on a new rail link through the alps (NRLA) made up of the Gotthard and Lotschberg routes that will eventually create a flat railway through Switzerland’s alpine ridge at a maximum elevation of 550 metres above sea level.
When completed, freight trains, longer and heavier than today, will be able to travel at a speed of 160 kilometres an hour over the route, increasing the capacity of transalpine freight to 50 million tonnes per year. Passenger trains will be able to travel at 200 to 250km/h cutting traveling times from Zurich to Milan by more than one hour.
The project scale
The extremely complicated construction of the AlpTransit project started in the 1990s and extends over a 25 year period, with the long implementation time taking in many new, and innovative, developments in construction standards and technology.
One of the biggest infrastructure projects in Europe ever, construction involves two base tunnel projects – Lotschberg and Gotthard. The 36 kilometre Lotschberg Base Tunnel was inaugurated in 2007, but the system will only be fully operational with the completion of the key project – the 57 kilometre long Gotthard base tunnel that is known as the AlpTransit Gotthard (ATG) project.
The Gotthard Base Tunnel is the main object on the new high-speed railway line between Zurich and Lugano, which also involves the construction of the Zimmerberg and the Ceneri base tunnels, both about 15 kilometres long. While the Ceneri project is currently under construction, the Zimmerberg base tunnel has been postponed due to financial reasons.
The Gotthard Base Tunnel will be the longest rail tunnel in the world when construction finishes in 2017, and consists of two parallel, single track running tunnels, cross passages every 325 metres, and two multifunctional stations on the third points of the tunnel allowing trains to change tunnels or stop in case of an emergency.
To save construction time, the tunnel was divided into five lots, two of which are situated near the portals at Erstfeld in the north and Bodio in the south. The three intermediate lots at Amsteg, Sedrun and Faido use access tunnels and shafts to reach the base tunnel levels that were completed 2001.
Construction started on the running tunnels and multifunctional stations in 2002 by consortium TAT – a joint venture of leading companies from Switzerland, Germany, Italy and Austria. The running tunnels are excavated by two giant tunnel boring machines (TBMs), while the multifunctional stations are excavated by traditional drill and blast methods. The excavated material is converted into concrete aggregates on site to produce sprayed and insitu concrete for the inner lining of the tunnel system.
At the time of writing, last month, the two 16 kilometre long running tunnels between Bodio and Faido had been excavated, together with the multifunctional station in Faido, and the two tunnel boring machines were making their way towards the intermediate access of Sedrun, while in Bodio the inner lining of the running tunnels and cross passages was being installed.
The logistics of a project this size are simply awesome. The giant twin TBMs are 10 metres in length and have cutting faces of 9.5 metres. They are also set up to carry primary support measures such as rock bolts, wire mesh and shotcrete.
At peak performance, a TBM can take make 38 metres a day. Waste from the TBMs is excavated by muck trains made up of two 35 tonne locomotives pulling 10 cars with a loading capacity of 24 square metres. The material is hauled out to a multi-car rotary tip near a recycling plant.
Massive amounts of concrete are produced for lining the tunnel sections. For the 16.5 kilometre Bodio section in 2001, for instance, a joint venture between Holcim and Sika produced one million cubic meters of in-situ concrete for the inner lining, and 250,000 square metres of sprayed concrete (shotcrete) for primary rock support and inner lining of caverns, crossovers, rescue and ventilation tunnels.
Concrete is moved from the batching plant by trains made up of four to five concrete mixer cars carrying 12 square metres of concrete and pulled by a 35 tonne locomotive. The batching plant has a capacity of 120 square metres an hour, and has already produced almost a million square metres of concrete. The maximum output for one day was 1200 cubic metres.
When going into operation in 2017, the Gotthard Base Tunnel will be the longest railway tunnel in the world, but there are many milestones to be reached, challenges to be met, and problems to be solved before the first train passes. Some of the rock conditions in unexcavated sections are still unknown, while logistic operations – as well as handling of high underground temperatures – are reaching new dimensions, bringing the staff and the underground workforce resource to its limits.
As always, the key to success is teamwork. The two ‘operational’ departments, TBM drives and inner lining, have to rely on the so-called ‘service’ departments, technical office, logistic and mechanical department, to be able to reach the high-set goals. Good relations to the client, the supervisor and the project engineer are vital to keep the project on track.
And not to forget the holy Barbara, the saint of all miners, who always has her place at the entrance of the tunnel, protecting the workers and giving them the spirit to finally reach the ultimate goal – breakthrough and light on the far side of the tunnel.
Contractor Vol.32 No.10 November 2008