BYLINE: Anabel Hengelmann
Getzner Werkstoffe GmbH
IN THE search for a smoother ride for street-running tram and light rail lines, Getzner Werkstoffe has been developing an elastic support structure for grooved rails over the past two or three years, in co-operation with Mannheimer Versorgungs- und Verkehrsgesellschaft AG. The system combines external and inner multi-layer hard foam cavity elements and an elastic rail base bearing.
Following detailed tests by the Institute of Road, Railway & Airfield Construction at München Technical University, the partners were ready to install a test length for practical trials. MVV identified a double-track section in Bismarckstrasse as a suitable site. This has street-running tracks shared by trams, buses and local traffic.
Installation of street track is a difficult and disruptive process, and a high priority was put on using a structure that could be laid rapidly. The ideal was a trackform that could be pre-assembled, but which permitted easy adjustment of rail height and direction during laying. The RhedaCity System developed by Pfleiderer Infrastrukturtechnik has been successfully proven in several cities, and was adopted for the Mannheim trials in combination with the Getzner embedded rail system.
The test section is 210m long, of which around two-thirds is straight and the remainder follows a 26·5m radius curve. Two weekend closures were made available for the relaying, each running from 21.00 on Friday until 04.00 on Monday morning. To ensure that the work could be completed in these two possessions, the track was pre-assembled at MVV’s workshops in Luzenberg.
The easy handling of the high-resistance foam cavity elements made the trackform easy and fast to handle during installation. All 270m of straight track was laid during the first weekend, but without the final surface layer. The remaining 150m of curved track and all the tarmac was laid on the second weekend.
Step-by-step
To simplify the installation procedure on-site, both the railfoot bearings and cavity elements were bonded to the rails using a two-part adhesive (1). The rails and sleepers were then assembled onto 15m long yokes. At each end of each yoke about 750mm of the rail was left without the elastic material so that the sections could be welded together on site.
To ensure that the grooved drainage cases move together, they were bonded using a thicker Sylodyn mat with a laminated mesh, which was cut to size and glued onto each yoke.
Adjustable and fixed wedge-shaped track profiles on the sleepers allow final alignment and fixing of the track following installation. The fixed profiles have a round hole, and the adjustable ones a longer slot. To prevent the track gauge shaking loose during transport, a guard rail tie bar is fitted at each end of a 15m yoke.
After delivery to site, the yokes were laid on the compressed subgrade, roughly positioned and welded together (2). The next step was to locate the track accurately in the exact vertical and axial position. Then the remaining cavity elements and base bearings were installed in the areas around the welded joints (3).
The concrete infill was laid in two stages. The first layer came up to the upper edge of the sleeper, being continuously poured along the centre of track from one sleeper crib to the next (4). As soon as the concrete had cured sufficiently, the supporting spindles were released so that the track could settle free of stress. The second layer of concrete was then poured to a height of 60mm below the rail head, and the spindles were removed.
After the second-pour concrete had been cured, the wet asphalt was poured and levelled. The ioints between the railhead and the road surface were later cut out and sealed with a bituminous compound. On two test sections a polyurethane resin filler was used instead.
Noise and vibration measurements were taken before and after installation by engineering consultant Uderstädt+Partner, to assess the efficiency of the mitigation measures. These found that any vertical deflection of the track during operation is absorbed by the Sylodyn bearings and converted into a transverse force.
Mounting the track with the mesh in the surrounding concrete guarantees rail stability and prevents the development of grooves. The good fit and simple use of the hardfoam cavity elements make the system easy to handle and allow rapid installation.
CAPTION: 1. Rails fitted with the Getzner elements are pre-mounted on Pfleiderer sleepers
CAPTION: 2. The pre-assembled yokes were positioned using two cranes
CAPTION: 3. After laying, the rails are welded and the track is aligned finally before concreting
CAPTION: 4. The infill concrete was laid in two stages, followed by the tarmac surface layer
