Towards smoother tracking

How innovations in overcoming track fouling are set to optimise rail performance.

Newly constructed or maintained ballasted track usually has clean, large, and uniformly graded ballast. With traffic accumulation, fine materials, such as degraded ballast aggregate, commodity material (coal, iron ore, grain), clay, sand, and other small particles, will penetrate the clean and uniformly graded ballast layer, leading to contamination, usually referred as fouling.

Fouling is unfavourable to track performance due to the reduced drainage, causing formidable engineering challenges. For decades, researchers and practitioners have been focusing on developing feasible track maintenance solutions to restore track drainage. However, the effect of popular maintenance activities on track drainage restoration under different fouling conditions is not well-understood.

The lack of comprehensive understanding of fouling migration through the ballast layer gives rise to challenges in correlating fouling profile with track performance, and raises arguments regarding the benefits of maintenance activities, such as shoulder cleaning.

Shoulder ballast cleaning is a cost-effective alternative to improve track performance and restore drainage. There are many advantages associated with the practice of shoulder ballast cleaning when compared with alternative track maintenance options; such as significant enhancements in productivity, less disruptive to the track substructure, and less resource intensive. Shoulder ballast cleaning optimises the productivity of ballast rehabilitation programs with less required track time, no speed restrictions, and less invasive work to the track structure allowing crews to capitalise on short track windows.

Loram HP SBC 

Loram’s High Performance Shoulder Ballast Cleaner (HP SBC) is the industry’s proven performer for heavy haul, freight and commuter railroads. With typical production of 1200 cubic meters of ballast per hour, the Loram HP Series leads the industry with superior value – measured as the best combination of production speed, depth of cut and quality of cleaning. 

Loram’s HP Series machines are self-propelled, equipped with twin 760 mm wide, high-capacity digging buckets to clean ballast up to 860 mm beyond the end of the sleeper reaching to the edge of the ballast section. These buckets dig as deep as 500 mm from the top of the sleeper at speeds up to 3.2 km/h. The integrated scarifier teeth simultaneously undercut the sleeper ends up to 30 mm, breaking up mud pockets and restoring drainage.

Vibrating separator screens on the Loram HP SBC clean and restore fouled ballast by removing dirt, mud, and fines more effectively than any other machine in its class. With Loram’s exclusive elliptical throw agitation and variable screen levelling from 9–19°, the separator screens on the HP Series provide distinct cleaning advantages over any other machine on the market. In wet conditions that are frequently encountered, the screen angle can be adjusted lower for greater cleaning action. In common ballast conditions, the screen angle can be adjusted higher, delivering increased cleaning speeds. The reclaimed ballast is repositioned on either or both shoulders to the specified track shape and the separated fines are discharged up to 8.8 metres from track centreline.

Effects of fouling

To gain insight of the effect of fouling on ballast drainage and particle migration behaviours, Loram is supporting research at the University of South Carolina, led by Dr Yu Qian, to perform both cutting edge numerical simulations and innovative laboratory experiments to bridge the knowledge gap between the fundamental engineering science and field practice. A full-scale track section is built in an innovative transparent ballast testing tank in the laboratory at the University of South Carolina to quantify the ballast permeability before and after shoulder cleaning or other types of ballast maintenance activity. Fouling particles and water are dyed and continuously tracked through high-resolution cameras to visualise the entire migration process of the fines. Track drainage restoration from shoulder cleaning or other types of ballast maintenance activity under different fouling conditions can be quantified and compared.

A fully coupled CFD-DEM (Computational Fluid Dynamics – Discrete Element Modelling) simulation model is also developed to study the detailed interactions between ballast, fines, fluid, and air to explore the correlation between parameters in micro-scope and track performance in macro-scale. Different from traditional flow net analysis, the numerical model developed in this study simulate individual fine and ballast particles for both saturated and unsaturated conditions. The effect of different rainfall intensities can be simulated with considering the dynamically evolving drainage paths as fines and water moving within the ballast aggregate skeleton. This model would also provide information that hardly can be measured in the experiment to help optimise the ballast maintenance practices, such as shoulder cleaning depth, width, and frequency. We can see there are example of how fine particles migrate during rainfall events and provides the local fouling index (FI) change based on the fine particle accumulation. 

The results indicate that:

  • Shoulder cleaning is highly effective in improving ballast internal drainage as the shoulder region is the primary flow passage for internal drainage.
  • Shoulder cleaning helps in migration of fouling material from the track centre to the shoulders by creating a flow path from track centre to the shoulders which effectively reduces track’s rate of deterioration and increases the ballast life.

Final thoughts

As we have seen, fouling is bad for track performance due to several reasons including reduced drainage. For decades, researchers and practitioners have worked on developing feasible track maintenance solutions to fix track drainage. Via the development of High Performance Shoulder Ballast Cleaner, Loram Maintenance of Way has taken a significant step towards solving these issues.

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