More than just a product

The fact that the slab track is more than just a product becomes apparent if the subject matter is approached from the perspective of the internationally active track construction company Heitkamp Rail, a subsidiary of the Dutch Heijmans group of companies.

Over a period of years, a very complex task field has developed around the slab track ranging from consulting and planning services to the execution of construction work and to internal developments. This task field is characterized by several track systems that – representing engineering projects by themselves – are often embedded in complex construction projects.

Light railway projects

Since the 70s, extensive and mostly underground light railway lines have been built in the Ruhr region to improve the infrastructure in Germany’s largest urban centre. For decades, the Heitkamp construction company from which Heitkamp Rail later emerged has been awarded numerous contracts in the area of tunnel construction, underground engineering and railway construction.

Heitkamp participated when in 1979 the Light Railway Building Authority in Dortmund commissioned the installation of a 4,200m long mass-spring track system in a newly built tunnel in order to meet the increased noise insulation requirements. As the available height from the top edge of the tunnel floor to the top edge of the rail was merely 62cm, only a combination with a slab track was considered. The system consisted of pre-fabricated reinforced concrete troughs that had been installed on elastomer springs on the tunnel floor. Each one of these troughs featured a recess into which a pre-stressed-concrete sleeper was placed, aligned and cast with a special mortar – it was the first time that a method of this magnitude had been used in Germany.

The fundamental planning principles are still valid – regardless of whether they are applied to rapid transit or intercity rail traffic: the lower construction height of the slab tracks compared to the ballasted track allows for smaller and thus more economical tunnel cross-sections. In conjunction with mass-spring systems the higher specific weight of the monolithic slab tracks is an advantage compared to ballasted tracks.

First slab tracks for Deutsche Bahn

In addition to contracts awarded by the municipal Light Rail Building Authorities, first contracts for the Deutsche Bahn followed. In the context of the S6 metropolitan railway line, a 1,000m long test track for the slab track Y-steel sleeper system was built in Langenberg near Cologne. This is a design where the Y-steel sleepers are placed directly on an asphaltic base course. A slot is cut into the asphaltic base course. The Y-steel sleepers feature web plates at the bottom which are located within the slot after the placing of the sleepers. The slot is then filled with a special compound so that the occurring lateral forces as well as the lifting forces can be absorbed. Three years later in 1994, the joint venture Brehna consisting of Heitkamp and Strabag started with the construction of 29,200m of slab tracks (Y-steel sleeper design) for the line linking Halle and Berlin – this is by far the largest section that has ever been built with this design.

The development of new slab track systems for intercity rail traffic

After the commissioning of the high-speed track Hanover-Wuerzburg and Mannheim-Stuttgart with a regular maximum speed of 250km/h, the trackbed’s quality suffered early degradations as the track ballast had been downright ground due to the high dynamic loads. This leads to increased maintenance so that the Deutsche Bahn put more emphasis on the life-cycle-costs. The German construction industry was called on to develop new, more efficient slab track systems. At this point, only 130km of tracks in eight different slab track designs were in operation. Finally, the German construction industry developed another seven systems. In 1996 they were installed into the DB railway network in sections of 390m within the course of the ‘Waghäusel’ test track and tested during the everyday operations.

Again, Heitkamp contributed its know-how and developed its own system. In its approach, this innovative system is very different from the other systems: Whereas five of the seven systems are sleeperless systems and the rail supporting points are directly supported by the concrete base, Heitkamp uses the experience and the modern equipment technology used for the construction of ballasted tracks. Applying the tried and tested track construction methods, a modified ballasted track is built in a concrete trough that is supported by a hydraulically bound base layer (HBL). Conventional, high-precision tamping machines are used for the tamping and aligning of the rails. By filling the hollow spaces in the ballast with a special cement paste, the exceptionally exact track position will be permanently fixed and the ballasted track becomes the Heitkamp slab track system. Surveys have confirmed the permanently exact track position even after years of operation. Finally, in March 2004, the Federal Railway Office in Germany approved the Heitkamp slab track system. Based on this, the system is currently further developed.

Slab tracks and mass spring systems for intercity rail traffic

The long experience gained from the construction of light railways with the special logistics requirements of a tunnel construction site as well as the professional competence in the production of slab tracks and mass-spring systems, allowed Heitkamp Rail to be awarded exceptional construction projects.

In the course of the construction of the new Cologne-Rhine/Main line, the Cologne/Bonn airport was linked with a 15km long track to the ICE network and the regional metropolitan railway. The track construction work executed in 2003 for lot three comprised a 5,450m long section which included the 4,200m long airport tunnel as well as the underground 4-track train station. The nearby housing development required two sections with a total of 1,440m track length to be equipped with mass-spring systems that feature eigenfrequencies of 7 Hz or 10 Hz. In order to meet these requirements, it was imperative to place the trackbed plates on single rail supports. For construction-related reasons the trackbed plates were cast on the tunnel floor in individual lengths of up to 205m. After a sufficient setting of the concrete, the trackbed plates could be hydraulically lifted and placed on elastomer single rail supports. This was followed by the installation of the ‘System Rheda 2000’ slab track system into the through-shaped section of the trackbed plate with the help of a device that was specifically developed to align and set the track unit. During the construction planning, it was especially the work on the neighboring lots as well as the equipment work taking place simultaneously that needed to be considered.

In Berlin, Heitkamp Rail was commissioned to plan and built the North-South link – the heart of the Berlin new railway centre – as the technical leader in a joint venture with ‘Porr Technobau und Umwelt’. This approx. 4km long underground track includes the 4-track regional train station ‘Potsdamer Platz’ and the 8-track intercity part of the new Berlin central station. The scope of services included the remaining rough work, the production of the slab track and mass-spring systems.

The protection from noise and vibrations required the installation of eight differently tuned mass-spring systems which makes it the largest connected mass-spring systems in the world.

Two slab track systems were installed: Rheda 2000 and the ÖBB/PORR system for the single-track tunnel sections often used in Austrian tunnels. Expressed in numbers all this means that 103,000m3 of concrete, 35,000m2 of elastomer mats, 6,585 elastomer bearings and 44,000m of rails as well as 54 point switches had been used.

In order to complete the project within a period of only 21 months, numerous construction phases were devised based on a sophisticated production and logistics planning.

International projects

Abroad, numerous projects were also completed. For example, at the beginning of the 90s Heitkamp was awarded the contract for the track construction work in the newly built channel tunnel as part of an international consortium. Approximately 100km of slab tracks (‘Sonneville’ system) were built between Folkstone and Calais. It was only recently that this system had been built for another international major project and also as part of an international consortium: In the course of the construction of the Taiwan high-speed line, 33km of the ‘Sonneville’ design was built in lot 200 primarily in tunnels. In France, we built 1,400m of the ‘Direct Fixation’ slab track system using ‘Vipa SP’ single supporting points from the Pandrol company. In this case, assembly devices developed by us were used which also ensured the correct track gauge and canting of the rail. In Austria, we could successfully install the ÖBB/PORR system in the Wolfsgruben tunnel. This year we will start replacing the existing track with an ÖBB/PORR slab track system in the directly adjoining 10,648m long and over 120 years old Arlberg tunnel. This requires extensive profiling work of the tunnel floor – while maintaining the railway service on the adjoining track. In China we have been awarded the contract to build a 10km long test track near the city of Wuhan. Later, this test track will become part of the new 1,000km long high-speed line between Wuhan and Guangzhou. Heitkamp Rail is responsible for the planning of the Rheda ‘2000’ slab track system, the examination of the substructures as well as for the site management during the construction.

Conclusion

As the described projects show, several factors play an important role if slab tracks are to be successfully planned and built.

Mostly complex logistics requirements and co-ordination tasks arise from new constructions. In particular, this is true for high-speed lines as the given route parameters and the local topography regularly lead to varying structures (tunnel, cut, bridge, dam). If slab tracks are to be installed into existing facilities, it will only be possible to work in sections and/or during service brakes. Moreover, if the sections to be renewed lie within a tunnel as described above in the case of the Arlberg tunnel, installation methods requiring complex logistics and equipment technologies have to be mastered.

Of course, it also requires detailed knowledge of the different systems available on the market. There are country-specific key aspects. Whereas in Germany the systems based on Rheda are most widely used for 76% of all systems in operation, the ÖBB/PORR system consisting of prefabricated track supporting plates is most commonly used in Austria especially in tunnels. In Switzerland, slab tracks from the Bözberg / Stedef / Sonneville LVT product line have become established. However, it is assumed that the international increase of high-speed traffic and the expansion of the European network will result in a further intermixing. In order to be able to provide the corresponding know-how, international projects are indispensable. The newly developed systems will also massively compete for international market shares in order to bring in the high development costs. This means for track construction companies to continue to attentively follow all developments and/or to actively participate in them. Development work and the will to innovate are the key to technical competence.

About the author

Mr. Andreas Michnik studied civil engineering at Dortmund University and began his professional career with the construction management of tunnel and engineering projects. Since 1999, Mr. Michnik has been responsible for the planning and preparation of complex engineering projects at Heitkamp Rail. During this time, numerous developments and patents have emerged.