The Gotthard Base tunnel is the longest tunnel in the world and burrows through the Alps in Switzerland.
Beneath the highest mountain peaks the tunnel courses some 2000 metres below the rock and lies only about 550 metres above sea level. It will carry freight loads of up to 4000 tonnes, 200 trains per day in each direction travelling at up to 250kmph.
Balfour Beatty Rail, as part of Transtec Gotthard joint venture, is providing total project management involving the design, installation and commissioning of rail infrastructure equipment for the tunnel as well as the equipping the two 57km single track tunnels and the adjoining, open north and south sections that connect to the existing rail network.
The work on the track, the overhead line system and elements of the supply system is being carried out in joint venture by Balfour Beatty Rail and various other partners (Alpiq InTec AG, Alcatel-Lucent Schweiz, Thales Rail Signalling Solutions and Alpine Bau GmbH).
The Transtec Gotthard Team work for Alp Transit Gotthard Ltd, the main constructor, who is responsible for the overall task of building the Gotthard Base Link between Zurich and Lugano.
The 1.7 billion Euro Project
The Transtec Gotthard team took two years at the design stage to plan its methodology and integration utilising a 250-metre test track. Complete semi-permanent bases have been set up some 5km outside the northern Erstfeld portal and in Biasca in the south, again about 5km from the Bodio portal.
Computerised logistic controls are installed, workshops, aggregate and cement stores and loading bays.
The rail track work illustrates the detailed and disciplined logistical organisation needed to do the work. Transtec Gotthard has invested in a carefully designed set of specialised plant and mobile machinery, some completely new, and on a large scale.
The machines, specially designed and developed for the construction of the slab track in the tunnel, included:
- Rail laying and flash butt welding
- Sleeper transport wagons and sleeper distribution
- Track panel assembly (rail lifting, sleeper assembly, inclination assurance)
- A support system for track fixation to provide easy handling and very high accuracy in track alignment of 0.5mm
- A rail bounded concrete mixing plant (The Concrete Train)
- A special concrete shuttle for transport in the tunnel
- A special concrete pouring machine and working platform
- A special moveable tent to protect the fresh concrete.
The Track Laying Operation
The 20-day production cycle begins with bringing in the steel rail sections. Rail lengths of 120m are pulled onto the tunnel floor by a tyred machine which runs back and forth and then butt welds them using a hydraulic arm. The tracks are supported with temporary fixings and the train runs forwards for a repeat cycle.
Fourteen special designed wagons bringing the single sleeper block system LVT which support the track, one on each side, a fitted crane picks up 60 blocks at a time and drops them through a slot into the centre of the track. Shuttering is added for the premade drainage ducts and crack inducers are installed. The track panel is constructed with the support of specially developed rail construction robot machines which fit to the special logistical boundaries of the tunnel cross section.
A highly mechanised production guarantees high quality and accuracy of the track alignment as well as supporting a safe and healthy work environment for the track workers.. Supports are greased to prevent sticking by the concrete, and protective covers are put over the rails. A laser surveying tool performs the final alignment check on the inner edge of the tracks to produce the necessary 0.5mm accuracy.
The Concrete Train, producing up to 235 m3 Concrete for two shift days, producing 215m of poured slab track. Within a 20 day working cycle only 10 days are needed for the concreting of the slab track. In peak times about 85 people are working in a three shift system for the finalising of the 2160m long section.
The Train, consisting of twenty-four wagons, pours the base over 115 km of slab track throughout the tunnel. Some 39km of ballasted track will be made outside the tunnel.
Aggregate wagons are linked along the train with conveyor systems which brings a carefully tailored mixture of sands, and sized stones, to a concrete batching plant wagon at the forward end of the train. Water wagons and cement wagons also feed their materials into the batcher under computer control using pumps or pneumatic lines. Finally, on the most forward wagon finally sits a Putzmeister pump for delivery. There is even a wagon where a concrete batch can be diverted from the batcher if it tests badly.
Exceptional track quality is achieved through repetitive construction of 2160m in a 20 day cycle producing 220m of linear slab track in 15 hours. 228.000 metres of rails, which is equivalent to 1.900 pieces of 120 metre long rails, were used for the slab track construction incorporating 1.900 flash butt welds and 380.000 pieces of LVT sleeper blocks.
As the finalised permanent track is the transport route, then the follow-on catenary and signal crews can carry on their carefully programmed sequences.
The railway infrastructure is designed for maximum availability and minimum costs with three key principles adhered to:
- Smallest possible number of points
- Straightest possible line
- Ballastless track in the tunnel for maximum stability
The Result
Once completed the journey time between Zürich and Milan will be reduced by sixty minutes allowing rapid transit between cities. The Gotthard Base Tunnel is designed for mixed freight and passenger traffic and will take a significant amount of Trans-Alpine freight from the road network onto the rail network once in operation. Passenger trains will be able to pass through the tunnel at a speed of 250kilometres per hour.
Commercial rail services are due to start through the tunnels in 2016.
