Build Better Tracks: Ballast & Sub-ballast Stabilisation with Geogrid

by Jonathan Cook, on 29-Jul-2021 08:53:23

For railways around the world, line speed restrictions and expensive and disruptive track maintenance are frequently caused by poor track geometry and misaligned rails. However, Tensar's trackbed stabilisation systems with TriAx geogrids have been proven to substantially reduce track maintenance, being the subject of extensive independent research and development and approved by Network Rail in the UK and National Rail Authorities worldwide. 

How TriAx Geogrids Work: Mechanical Stabilisation

Tensar TriAx Geogird Mechanical InterlockTriAx® geogrids stabilise ballast and sub-ballast layers through the principle of “mechanical interlock.” When unbound aggregate is compacted over a geogrid, the coarser particles partially penetrate through the geogrid apertures and lock into position. The load distribution over the underlying subgrade is enhanced, increasing its effective bearing capacity. The geogrid’s ability to confine aggregate particles significantly reduces lateral spreading of granular particles, a major cause of ballast and sub-ballast settlement. This video shows a side-by-side comparison demonstrating how TriAx geogrid works to combat settlement compared to an unstabilised track. 

GeoGrid_09_17

Side-by-side comparison demonstrating how TriAx geogrid works to combat settlement compared to an unstabilised track
(Video source: Tensar Corporation USA)

Tensar TriAx geogrids are used to stabilise the trackbed structure in two ways:

Sub-ballast Stabilisation

Installed at the bottom of the sub-ballast, TriAx geogrids help distribute imposed loads more efficiently over the underlying subgrade, leading to a reduction in the required sub-ballast layer thickness. 

Benefits of sub-ballast stabilisation include: 

  • Maintaining track geometry for longer
    Incorporating TriAx in sub-ballast layers can reduce the rate of track settlement, maintaining track geometry for longer and extending ballast life.

  • Saving time and money on construction
    Sub-ballast layers stabilised with TriAx are up to two-thirds thinner, while maintaining bearing capacity, and excavation and replacement of weak subgrades is reduced, cutting construction time and costs.

  • Improving sustainability
    Reduced excavation and disposal of unsuitable material, along with reduced need for imported materials delivers carbon savings.

Tensar Railway Solutions - Improved Bearing Capacity

Ballast Stabilisation

Installed between the ballast and sub-ballast layers, TriAx geogrids limit lateral particle migration and thereby minimise track settlement. This helps increase the period between maintenance cycles by three to five times.

Benefits of ballast stabilisation include: 

  • Robust trackbed
    Using TriAx can reduce the rate of ballast settlement and reduce traffic-induced degradation, delaying sleeper settlement, maintaining track geometry for longer and extending ballast life.

  • Reducing maintenance
    Maintenance intervals can be up to three times longer, if mechanically stabilised ballast is used.

  • Reducing life cycle costs
    The use of geogrid in ballast can reducing whole-life costs, in terms of both cash and carbon.

Tensar Railway Solutions - Maintenance Reduction

Want to understand more about the benefits of stabilising geogrids on the railway?
Then check out Andrew Lee's previous Ground Coffee blog here.

Meet Tensar's Rail Team at Railtex Infrarail 2021

Tensar trackbed stabilisation systems are used internationally, delivering track construction and renewal schemes quickly, economically and safely. Our geogrids are used to mechanically stabilise track ballast, sub-ballast and blanket layers; to increase trackbed stiffness, reduce variability, minimise track settlement and ballast degradation.

UK Rail Team

To find out more, meet Tensar's Rail Team at Railtex Infrarail 2021 at the Birmingham NEC, UK at Hall 12,  Stand G56. 

Register now and get your free exhibitor's pass. 

Our rail division is a part of Tensar's strategy to grow the use of our geogrid-based engineering solutions in the sector. The division will be headed up by Peter Matthias as Major Projects Design Lead for Rail and Darren Evans, Major Projects Account Manager for Rail. Having a dedicated rail division will enable us to fully support clients in the sector over the coming years.

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