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Slabtrack gives a smoother ride in Swiss rail tunnel

As part of Swiss Railways' Bahn 200 programme, a new line is being constructed between Mattstetten and Rothrist. This will take the strain off existing lines and cut the travelling time between Zurich and Bern to less than an hour.

The new route involves the construction of a two-track tunnel in the canton of Argau, bypassing the village of Murgenthal. With a diameter of 10.65m and 4,742m long, the first 425m of the tunnel from the western portal was constructed in open cut. The remainder was driven through the rock strata of the lower freshwater molasse using a TBM.

Modern high speed trains place huge requirements on the loadbearing capacity of the tracks and their support. Traditional crushed stone ballast has limited applications for the rail traffic of the future. Tracks lying on or directly embedded in a concrete slab have been found to be more suitable.

Slabtrack has a number of virtues including high loadbearing capacity and comparatively low maintenance and repair requirements. And accurate track geometry results in a smoother ride for passengers and less wear on train suspension systems.

Compared to traditional ballast, the cost of laying slabtrack is almost double, but viewed in the long term, the benefits justify the investment.

Slabtrack has been in use in Germany since the 1970s, but in Switzerland it is only permitted in tunnels. The contract for slipforming the concrete trackbed and verge for the new Murgenthal tunnel was awarded to GrisoniZaugg by main contractor ARGE Tunnel Murgenthal. Contract value was around Swiss Fr8M ($4.76M).

The unreinforced track bed was produced from B40 concrete using a Wirtgen SP 500 slipform paver.

The 133kW unit has proved highly successful since its 1991 launch, with more than 100 units sold worldwide. Grisoni-Zaugg took delivery of its machine at the end of 1999.

Delivery time of the concrete to the paver proved to be a limiting factor on progress. As this could sometimes be as much as 40 minutes, a retarder was added to the mix. It also held slipforming progress to around 200 linear metres a day against the theoretically possible 400 linear metres. Work took place in 10-hour shifts on four days each week.

A high degree of accuracy was required. Maximum superelevation permitted was 5.2%, with minimum curve radii of 1,600mm. GrisoniZaugg used a Leica total station combined with a control system supplied by French company D&P Systems. The link was provided by radio modem.

Repositioning of the total station proved to be necessary every 80m, but the client placed reference points on the tunnel walls every 50m.

Using the wire-free guidance system with the Wirtgen SP 500 produced a good quality result, well within the permitted tolerances.

This prompted the contractor to use the SP500 for the walkways with integrated channel.

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