~ A geopolymer solution for rail infrastructure ~
The world’s railway network spans over 1.3 million route kilometres. Dating back to 1825, when George Stephenson’s steam-powered Locomotion No.1 transported hundreds of passengers to great fanfare, it set in motion an engineering journey that continues to evolve. Since then, rail engineering has advanced from wooden rails to high-speed steel. Here, Andy Lee, vice president of engineering at subsidence expert Geobear, explains how geopolymer technology is improving rail infrastructure.
Transition zones, the weakest link
One of the most significant engineering challenges in rail infrastructure lies in rail transition zones — regions where the stiffness of the trackbed changes abruptly over a short distance. An example of this is the transition from ballasted to ballastless track; such transition zones are commonly found at approaches to bridges, tunnels, viaducts, culverts and level crossings.
The sharp change in track stiffness causes an abrupt shift in structural support. This leads to accelerated degradation of track geometry, higher maintenance demand and reduced ride quality, earning transition zones the reputation of being the “weakest link” in the railway system.
Between 40 to 75 percent of railway operating costs are spent on track maintenance, with transition zones requiring significantly more attention than open tracks. Many factors contribute to the deterioration of these zones, including trackbed composition, load characteristics and transition design.
Differential settlement typically occurs between tracks placed on an embankment and the section built over a rigid structure. This results in divergence in track geometry, which amplifies the interaction forces between train wheels and rails. These increased forces further exacerbate settlement, creating a self-reinforcing feedback loop that continues until a maintenance team intervenes.
Various methods have been used to reduce stiffness discontinuities, including resilient sleepers and gradual adjustments to sleeper length and spacing, but these solutions are often costly and difficult to implement on active railways. Current design solutions include approach slabs and transition wedges, which are selected according to the local soil conditions of different countries.
The rise of high-speed rail
High-speed rail is defined as a railway line with top speeds exceeding 125 miles/hour. China leads with the world’s largest high-speed rail network, while Spain and France remain at the forefront of high-speed rail development in Europe.
In these systems, transition zones experience accelerated degradation because high-speed trains impose greater dynamic forces than slower trains, which in turn accelerate differential settlement in these already vulnerable areas.
Soil-cement stabilisation is a common method used in high-speed rail to prevent differential settlement in transition zones. For high-speed lines in France, a layer of cement-bound material is typically placed above wedge-shaped zones of granular material to smooth abrupt changes in track stiffness.
Geopolymer technology: a new approach
In response to the engineering challenges posed by transition zones in railway infrastructure, Geobear has introduced a patent titled “Railway track bed strengthening”. The patent outlines the application of geopolymer injection technology for railway maintenance and repair. One of its core advantages is efficiency, providing a faster and less disruptive alternative to traditional methods that typically involve extensive track excavation and substantial downtime.
By avoiding excavation, heavy machinery, and the transportation of large volumes of materials, the geopolymer method reduces carbon emissions by up to 75 percent, compared to conventional techniques.
A key use case of the technology is addressing the long-standing issue of degradation in railway track bed transition zones. Targeted geopolymer injection progressively reinforces and strengthens the subgrade beneath the ballasted track section as it approaches the bridge abutments. This treatment generates a smooth transition, the solution increases passenger comfort, maintains line speed, and reduces the risk of derailment.
The patented solution uses geopolymer resin to treat transition zones, with the formulation tailored to suit specific soil types. In cohesive soils like clay and silt, the geopolymer spreads by a process known as hydraulic fracturing, expanding and solidifying to improve both bearing capacity and stiffness modulus.
Technicians inject the geopolymer at varying depths to produce a gradual and stable change in subgrade stiffness, effectively protecting and prolonging the integrity of transition zones. This solution is customised to suit the soil type and environmental conditions. The length of the transition zone is determined by factors such as traffic load, train speed and existing soil stiffness.
Geobear implemented this technique in the transition zone at Sarsfield Road UBC4, Dublin. In this case, the transition zone was located in an area from a ballasted track to a concrete slab track as the rail passed over an elevated bridge above a road.
Beyond transition zones
While the patent addresses the need for an alternative solution to rail transition zone maintenance, geopolymer resin injection technology can also be used across a range of other rail improvement scenarios.
Geopolymer resin injection has been implemented in rail infrastructure repair and maintenance globally. In many cases where transition zones undergo significant settlement, subgrade ground improvement will be required. This was the case at Stoke Canon level crossing on the South West Mainline, UK, a high-speed ballasted rail line operating at 100 miles/hour and carrying ten equivalent million gross tons per annum of traffic.
Rapid deterioration and poor track geometry at this location were attributed to subgrade erosion caused by soft underlying ground and inadequate drainage. Ground engineers implemented a solution under Rules of Route within isolated possessions. The intervention objective was to improve the ground and prevent further deterioration, not to lift the track.
This technology offers a unified solution that can be consistently applied throughout the rail industry, while still being adaptable to the diverse ground conditions found in different regions. It’s a globally scalable approach that is reliable, efficient, and environmentally conscious.
But the impact extends beyond engineers and rail operators. Railways are a vital part of everyday life, connecting people to work, loved ones and opportunities. By reinforcing the reliability of rail infrastructure, this solution helps reduce delays, supports higher speeds and improve passenger journeys.
To learn more about Geobear or to discuss your ground-engineering challenges, visit www.geobear.com/infrastructure/segments.
