AT the end of last year Alstom took another step in the development of its next-generation New Ballastless Track (NBT) slab track system with the launch of the first 1520mm-gauge trials at the VNIIZhT test centre at Shcherbinka near Moscow.
Working in cooperation with Russia's Roszheldorproekt design institute, Alstom installed a 125m-long section of NBT at Shcherbinka, including two 25m-long transition zones. During the first phase of testing, loaded trains have run over the section of track at speeds of up to 80km/h. The most stable configurations will be put forward for high-speed testing, which will involve the construction of a longer slab-track section.
The life-cycle tests will assess the performance of various slab track configurations with the aim of certifying the system for use on high-speed lines. Alongside NBT other slab track systems are also being evaluated at Shcherbinka to determine which systems are most suitable for Russian conditions.
Launched in 2007 with the support
of the French Ministry of Industry,
the development of NBT was a collaborative venture between Alstom and five partners:
- Vossloh Cogifer - turnout design
- CEF - monitoring
- Ifsttar - design and laboratory testing
- Railtech - slab and fastener design, and
- French Railway Network (RFF) - customer.
NBT has been conceived with a design life of 100 years and is intended to meet the requirements of operations ranging from heavy-haul freight with 25-tonne axleloads to 360km/h high-speed operations. Other key design parameters included the need to accommodate cant in curves, compatibility with level crossings, a small footprint, rapid installation, low maintenance, and easy repair in the event of localised structural damage. The system is therefore designed to enable 4.8m-long slabs to be removed and replaced if required.
The slab is formed of two layers, with a foundation layer made of C25/30 concrete supporting a continuous reinforced C35/45 concrete slab, which is designed for direct insertion of the fastening system. The lower slab has a longitudinal shear key to ensure lateral stability between the upper and lower slabs. The lower slab sections are 2.8m wide and 30cm deep, while the upper layer is 2.5m wide and 24cm deep.
The system uses Pandrol Single Fastclip fasteners, enabling adjustment of ±20mm laterally and ±30mm vertically. Special fastenings are employed for switches and crossings, with Vossloh Cogifer's 300W fastening used as the reference design.
Where the NBT meets conventional ballasted track a 25m-long transition zone is installed with rail stiffeners and a graduated change in the stiffness of the rail pads.
NBT is designed for installation using Alstom's Appitrack mechanised tracklaying system. The system can lay up to 500m of track in a single day, giving NBT a faster rate of construction than other slab track systems.
Following provisional accreditation by RFF and independent RAMS certification by Certifer, the first deployment of NBT was completed in December 2013, when trains began running on a 1km double-track section of slab track near Eragny-sur-Epte on the Gisors - Serqueux line in northern France. Both rolling stock and track were instrumented to monitor the performance of the system, and after a year of monitoring Alstom says the data gathered was consistent with the values predicted during development.
Alstom says extensive research on life-cycle costs show the return-on-investment compares favourably with other slab track systems and ballasted track. Life-cycle analysis was based on a theoretical NBT installation on a 100km line used by high-speed passenger trains as well as freight, with sections of tunnel and viaduct. The assumed lifespan was 50 years and Rheda was used as the reference slab track system for comparison. Track construction costs were based on Alstom data, while maintenance cost data came from SNCF Network (formerly RFF) and Setra.
This showed that the construction cost of NBT was below existing slab track systems but still 15-20% higher than ballasted track. However, the reduced maintenance and operating costs of NBT mean the system would be cost neutral with ballasted track after 13-20 years in service. Furthermore,
this research suggests additional cost benefits could be derived from the higher availability of NBT.