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Mountain drive

One British contractor has broken into the lucrative Swiss tunnnelling market. Steve Turner reports

British contractors have long been accustomed to working on major international projects. But the UK's Balfour Beatty counts itself lucky to be in the idyllic setting of Switzerland as part of the Arge MaTrans joint venture working on the Lotschberg tunnel.

The Lotschberg and Gotthard tunnels form part of the country's massive Alptransit rail upgrade and account for some SFr10bn of the SFr30bn ($6.1bn) spending, which was backed by a referendum in 1998.

Running from Frutigen in the north to Raron in the Valais region, the Lotschberg tunnel aims to provide a faster route for passengers and freight through the Alps. It will reduce the growing amount of heavy traffic on the region's roads and connect Switzerland to the European high speed rail network.

'At present the train has to snake its way through the mountains. We needed a fast route for traffic travelling north-south across Europe, ' says Andreas Siegrist of BLS Alptransit, which has the commission from the Swiss government to implement design and construction of the project.

Balfour Beatty's involvement covers the Steg/Raron section. Two of its tunnel drives will be by tunnel boring machine and the shortest by traditional drill and blast.

At Steg, work on a 8.5km length got under way at the start of October 2000. The 9.4m diameter Herrenknecht TBM is now in its stride and edging toward 20m of tunnel a day. Transverse hydraulic rams of the 150m long, gripper type machine act against the rock walls and push the monster forward.

A system of conveyors transports the hewn rock out of the tunnel to a processing plant where stone is recycled for use as aggregate.

A team of 15 tunnellers works round the clock in eight hour shifts. Progress to date has been excellent with more than 800m of tunnel driven.

Balfour Beatty shift engineer Dietmar Reuter explains that the TBM uses laser guidance to work to a tolerance of 110mm.

The tunnel is being driven at a relatively low altitude to keep gradients to a minimum and enable higher train speeds. But this means temperatures in the tunnel are gradually rising. An efficient air conditioning system has had to be put in place to make working conditions bearable.

Geologically, the area is good for tunnelling, the rock being a mixture of granite, granodiorite and limestone. The TBM at present is cutting through this 'like cheese' Reuter says, leaving a smooth finish to the rock surface, a characteristic he hopes will continue.

Water expandable rock bolts are being used to strengthen the tunnel, with steel support mesh bolted on to the tunnel lining to protect the miners underneath. Sprayed concrete forms an initial lining to support the tunnel integrity.

A permanent 250mm concrete lining will be cast insitu along the length, once all tunnelling is complete in approximately two and a half years time.

Just a few hundred metres to the east, preliminary work on Raron's double portals is well under way. Blasting into the mountainside has begun at the start of the shorter length, to be constructed using traditional drill and blast methods. Meanwhile, support beams are being cast at the entrance to another 10km section, for which a second TBM is being brought in for a start in April.

Space is the biggest constraint at the Raron portals, as Balfour Beatty team leader Mike Grace explains. 'The working area is tight. The River Rhone acts as a very tight border to the site and the privately owned concrete plant on the site has to remain in operation.'

So although there can be no excuses for the late delivery of concrete, careful planning is essential.

Balfour Beatty is tendering for further work on the longer Gotthard tunnel to the east and commercial manager Malcolm Lorimer is hopeful.

The client seems happy with Balfour Beatty and the staff are more than keen to stay.

Geology range

Both the Lotschbe rg and Gotthard tunnel alignments run through a wide va riety of ext remely complicated geology, ranging f rom silts, gravels, conglomerates and chalk, to igneous and metamorphic granites, gneisses and phyllites, as well as volcanic dykes.

The Gotthard tunnel passes through three massif sections of granites and gneisses that sandwich two relatively thin sedimentary zones. The Piora syncline contains greywackes (coarse grained sandstone), gypsum, anhyd ri te and dolomite. The dolomite is often ext remely unstable and appears as a fine white 'sugar crystal' sand. This was encounte red during construction of the Faido access shaft about 350m above the main running tunnel level, causing massive ingress of sand and wate r at pressures up to 100bar.

Fortunately, further exploration revealed the rock on the alignment to be stable dolomite marble or dolomite and anhydrite, with no groundwater present.

The Tave tch zone further north will also present problems for tunnellers. It consists of a 3km wide section of heavily fractured and unstable phyllites, schists and gneisses that will probably have to be excavated using drill and blast methods.

The Lotschbe rg tunnel does not escape the problems either. Where it splits into two tunnels at its southern end, investigations revealed a 400m deep trough beneath the Kandersteg area, infilled with wate rlogged mountain slide debris. This led to an alignment change to the weste rn side of the Kander Valley which is solid rock. Geology In the northern part of the area consists of irregularly folded rock layers, which could also prove difficult.

Because the tunnels run at up to 2,300m below the Swiss Alps, ext reme pressures at these depths could also cause seve re disto rtion of the tunnels.

Tunnel progress

Alptransit lies at the core of Switzerland's rail modernisation plan which aims to remove heavy goods traffic from the country's road system and link into the European high speed rail network. The scheme has been more than a decade in planning after the Swiss government banned 40t trucks from its roads, which has led to congestion in surrounding countries as drivers divert.

Once completed, Alptransit will speed traffic through the tunnels with freight travelling at 160km/h and passenger trains at 250km/h.

The Neue Eisenbahn-Alpen Transversale (NEAT) project involves driving two massive tunnels through the Alps. The new Gotthard twin tunnel will be 57km long when completed - the longest rail tunnel in the world - and the Lotschberg tunnel 34.6km.

Most importantly, the new tunnels will be driven at low altitude. The highest point of the current Gotthard rail tunnel is 1,100m and two locomotives are need to haul a 1,300t train up its 27% gradient. Highest point of the new Gotthard will be 550m and neither tunnel will have a gradient of more than 12.5%.

Work on the Gotthard tunnel is progressing although a number of contracts remain to be let.

The Erstfeld site is scheduled to start up sometime this year. At Amsteg, the 1,784m access tunnel is complete and preliminary works for the section to Sedrun are under way. The shaft foot cavern at Sedrun is currently being enlarged, while at Faido the access tunnel is well past the 1km mark with the bypass tunnel at Bodio not far behind.

Driving tunnels at depths of up to 2,300m presents contractors with considerable difficulties.

Temperatures in the Gotthard tunnel could reach as high as 48degreesC, and 40degreesC in the Lotschberg, making cooling and ventilation high priorities.

There is also the question of how the rock will behave. Prediction cannot be 100% accurate even after extensive investigation and construction of trial tunnels, and practical experience of tunnelling at these depths is limited.

Completion of the entire project is scheduled for 2012.

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