The behaviour of ballasted track foundations: Track drainage and geosynthetic reinforcement

Ballasted Rail tracks are widely used throughout the world due to its resiliency to the repeated wheel loads, low construction cost and ease of maintenance. However, the ballast layer needs periodic maintenance due to its deformation and degradation associated with particle breakage and fouling. A proper understanding of the contamination due to various types of fines and its implications on track drainage is a pre-requisite for effective implementation of track maintenance operations. A new parameter Void Contaminant Index (VCI) can accurately assess the contamination as it includes the effect of void ratio, specific gravity and gradation of ballast and fouling material. A series of constant head hydraulic conductivity tests using a specially designed large-scale permeability apparatus were performed on fresh ballast mixed with different proportions of fines to study the relationship between the percentage of fouling and drainage characteristics. A field trial is conducted on an instrumented track at Bulli, NSW Australia, to study the benefits of a geocomposite layer installed at the ballastcapping interface, and to evaluate the performance of recycled ballast in comparison to traditionally uniform fresh ballast. It is found that recycled ballast can be effectively reused if reinforced with a geocomposite. The geocomposite can effectively reduce vertical and lateral deformations of the ballast with obvious implications on improved track stability thereby reducing maintenance costs.