Slab track, also called ballastless track, is a modern form of track construction which has been used successfully throughout the world for high speed lines, heavy rail, light rail and tram systems.
Slab track technology offers proven higher performance in service and a longer life than traditional ballasted track.
On traditional ballasted track, the rail is mounted onto a wooden or concrete sleeper. The sleeper sits on a bed of ballast (crushed rock) which distributes the loading to the subgrade. “Top” ballast is placed between the sleepers and on the shoulders to provide longitudinal and lateral stability.
Traditional ballasted track has been used since the earliest days of the Victorian railways and has changed little in concept since that time.
Ballasted track is relatively quick to lay, and readily maintained by a fleet of specialist track maintenance equipment. However, the nature of ballasted track means that the track can and will move under load; routine maintenance is always required to restore line and level, and clean or replace ballast regularly.
With concrete track slab systems, the ballast is replaced by a rigid concrete track slab which transfers the load and provides track stability. Resilience is introduced into the track system by means of elastomeric components. These may be pads, bearings or springs depending on the type of slab track system.
There are broadly five types of generic slab track system:
Within each generic group there are a large number of variants and proprietary systems available. Slab track can be designed and optimised to suit the required application.
Slab track offers the following advantages over traditional ballasted track:
Slab track systems require little routine maintenance. An inspection regime is, of course, necessary, but because the track is fixed in position there is no requirement for regular realignment of the rails.
The very low maintenance requirement also means that track workers spend less time trackside, improving worker safety.
There are examples of slab track installations where little or no maintenance (including rails and pads) has been carried out for over 25 years.
Shallow Construction depth
Many slab track systems require less construction depth than the equivalent ballasted system. Embedded rail systems and resilient baseplate track types require the least depth. This is an advantage in tunnels where headroom and gauge clearances are particularly important.
Reduced dead load
On structures, the reduced construction depth means reduced dead load.
Reduced structure gauge
Because slab track is fixed in position and will not move out of line or level under load, a reduced structure gauge can be used. This means that tunnel bore dimensions can be reduced, or higher running speeds can be achieved.
Higher speed operation
Concrete slab track offers a greater degree of trackbed stability than ballasted track. Therefore higher running speeds are achievable.
Experience with use of ballast at high speed (350 kph) has shown that fine particles can be sucked out of the track by the passing train. These particles are deposited on the rail surface and cause damage when run over by the wheels. In some areas this has required use of glued ballast to stabilise the track bed.
Engineered noise and vibration performance
Slab track can be designed to meet the required performance criteria in terms of noise and vibration. The slab track system can be selected to suit particular requirements e.g. booted sleepers or floating slab will perform well for locations sensitive to ground-borne vibration. Within each generic system, the resilient components can be selected to optimise the balance between acoustic performance and rail stability.
Long design life
An estimate of design life for traditional ballasted track is around 15 years, (see Britpave's Life Cycle Study) After which, the track requires renewal.
A concrete track slab is typically constructed with a design life of at least 60 years.
Increased reliability & availability
Slab track systems are more reliable than ballasted track, requiring little routine maintenance. Consequently fewer possessions of the track are required for maintenance, increasing the availability of the track for running trains.
Low whole life cost
Although the capital cost of slab track systems is usually higher than the equivalent ballasted track, the long design life and minimal maintenance requirement for slab track systems means that overall their whole life cost is lower than that of traditional ballasted track.
In the past, slab track systems were seen as expensive. While this is still true for the most sophisticated systems e.g. floating mass-sprung slab, for many systems the ongoing innovation and optimisation of slab track design is now reducing the capital cost to a level equivalent to ballasted track, without compromising performance.
A sustainable solution
In 2007, Britpave, together with NTEC carried out a comparative study into the sustainability of concrete slab track and traditional ballasted track. The study looked at an environmental life-cycle analysis through the whole life of the track including source of materials, manufacturing, construction, maintenance, decommissioning and recycling.
The study found that due to the long design life and low maintenance requirements of concrete slab track, it was the more sustainable option over a 60 year and 120 year lifecycle.
Slab track has been used successfully on many projects around the World:
|Duerne||The Netherlands||Embedded Rail|
|Best||The Netherlands||Embedded Rail|
|Crewe-Kidsgrove||UK||BBEST Embedded Rail|
|High Speed Line HSL-Zuid||The Netherlands||Rheda 2000|
|Cologne-Frankfurt High Speed Line||Germany||Rheda Züblin|
|Hibel & Prestbury Tunnels||UK||Rheda 2000|
|Nuremberg-Ingolstadt High Speed Line||Germany||Rheda 2000FF-Bögl|
|Taipei and Kaohsiung High Speed Rail||Taiwan||Rheda 2000|
|Eje Atlantico||Spain||Rheda 2000|
|Guadarrama Tunnel||Spain||Rheda 2000|
|Beijing-Tianjin Intercity Railway||China||Rheda 2000|
|TGV Méditerranée||France||Sateba booted sleeper|
|Channel Tunnel||UK/France||Sonneville block|
|Channel Tunnel Rail Link Phase II||UK||Booted sleeper|
|Gotthard Tunnel||Switzerland||Booted sleeper|
|St. Pancras||UK||Resilient baseplate|
|Docklands Light Railway||UK||Resilient baseplate|
|Athens Attiko Metro||Greece||Booted sleeper|
|Hong Kong MRT||Hong Kong||Resilient baseplate Floating track slab|
|Kuala Lumpur Star LRT||Malaysia||Resilient baseplate|
|London Underground||UK||Resilient baseplate|
|Tramway de Grenoble||France||Booted sleeper|
|Nottingham Express Transit||UK||Embedded Rail|
|Sheffield Supertram||UK||Embedded Rail|