Schedules are significantly impacted by trackbed upkeep and line speed restrictions, which are also costly and disruptive for the general public, the economy, operators, and asset owners.
Assisting railroad tracks
Rails and sleepers are traditionally supported by ballast and sub-ballast above the subgrade on railroad tracks. A different option is "slab track," where the rails sit on pads supported by a concrete base and are used, for instance, on bridges, in tunnels, and for some high speed lines.
When used together, ballast and sub-ballast provide the bearing capacity needed to handle the dynamic loads brought on by trains. The sub-ballast layer's thickness depends on the subgrade's strength, while the ballast layer itself is normally 300mm thick.
Upkeep of railroads
As a result of subgrade, ballast, and subballast deformation, which frequently results in speed restrictions, poor track geometry and the loss of vertical and horizontal alignment of the rails are typically addressed by railway maintenance. As ballast settles over time, more aggregate must be added on top and it must be tamped down.
Mechanical sub-ballast stabilisation lowers maintenance
Mechanical stabilisation of sub-ballast layers using geogrids is a tried-and-true method that can lower maintenance costs by reducing traffic-induced degradation. It has been used since the 1980s.
When ballast or sub-ballast is compacted over a geogrid, a strong and positive interlock is made when the ballast or sub-ballast partially penetrates and projects through the geogrid's apertures. Granular material is contained and prevented from spreading laterally, maintaining rail alignment along both the horizontal and vertical axes.
By expanding the area of influence on the subgrade, mechanically stabilised sub-ballast is better able to distribute loads, resulting in lower bearing pressures. Comparing stabilised sub-ballast layers to non-stabilized sub-ballast layers, the improved bearing capacity means that the rate of track settlement is slower, the track geometry is maintained for longer, and the life of the ballast is increased tenfold.
By lessening the effects of differential settlement, track profiles can also be smoothed at interfaces between structures, such as where embankments meet slab track beneath overbridges and in tunnels.
Additionally, mechanically stabilised sub-ballast layers can be up to 50% thinner while still maintaining bearing capacity, reducing the need for excavation and subgrade replacement, and speeding up and lowering the cost of construction.
Geogrid stabilisation allows lower quality materials to perform better than higher quality, non-stabilized materials. Given that it allows for the reuse of fouled ballast materials as sub-ballast in both new track construction and rehabilitation, this could have a significant positive impact on costs and sustainability.
Generating savings over the railroad's lifetime
There is a clear need to provide safe permanent ways quickly, with designs that offer value for money and little environmental impact, given the mounting pressure on rail infrastructure. Over the course of the railway's operational life, stabilising geogrids integrated into the sub-ballast can assist in lowering costs in terms of both cash and carbon emissions.
