[11/6/2009 ]
Unique track construction in Citytunneln
In the tunnels underneath Malmö a new, highly-damped ballast-free track is being laid in order to reduce structure-borne noise in the buildings above the tunnel. The track is being constructed by Austrian Rhomberg which is a subcontractor to Citytunneln’s railway contractor, Banverket Produktion.
Ballast-free track means that the rails and sleepers are not supported on crushed stone. Instead, specially-designed sleepers are cast in concrete. The sleepers themselves are concrete, and on the underside there is a dense, vibration-damping cushion with everything encapsulated in a rubber coating. (See diagram below)
This method ensures that train-induced vibration, which can be transmitted to buildings above ground, is reduced. Structure-borne noise is therefore considerably less than with conventional track using sleepers laid on stone ballast. Another advantage of ballast-free track is that it needs less maintenance.
Construction of ballast-free track
All track work activities take place in the direction from Holma to Malmö C. The track is first laid in the western tunnel, and then in the eastern tunnel. Concrete sleepers and rails were transported into the tunnels during the summer and early autumn.
The sleepers are laid out in the track area, and then the rails are lifted into place and fixed firmly with a special locking system. The rails with the fixed sleepers are then raised from the tunnel base and supporting concrete blocks then hold everything at the correct height above the base. Specially-designed tie rods are laid out at equal intervals to ensure that the correct gauge is maintained. The track is then finely adjusted in three separate stages.
Lastly, the concrete that supports the sleepers is laid. This is carried out using a track-going concrete layer about 300 meters in length which runs on the fine-adjusted track. The concrete is re-filled from a special concrete truck which runs a shuttle service from Hyllie to the concrete layer in the tunnel.
Schedule
Track construction in the tunnel is being carried out 24/7, with some 40 track-layers from Rohmberg working in shifts. About 200 m of track is completed per day.
Tracklaying is now in progress in the western tunnel, and is estimated to reach Malmö C in November. Construction will then start at Hyllie in the eastern tunnel, and the whole section should be finished by February. Finally, all points and crossings between Hyllie station and the tunnel entrance, as well as in the area of Malmö C Lower will be completed.