Effect of Tyre Derived Aggregates (TDA) on Permeability Behaviour of Railway Ballast.

Abstract

Ballasted railway tracks are the most preferred railway track system in many countries, including Sri Lanka, because of their numerous benefits. Nevertheless, during track operation, ballast degradation and track settlement are major issues that require frequent maintenance. To mitigate these issues, the application of elastic materials such as tyre-derived aggregates (TDA) has gained popularity due to their promising benefits. Mixing TDA with ballast aggregates has been identified as a potential solution to reduce ballast degradation, minimize frequent maintenance requirements, and ultimately improve track performance. However, mixing different size ranges and percentages of TDA with ballast alters the void ratio of the ballast, affecting its permeability characteristics. Hence, the impact of TDA-mixed ballast on the hydraulic conductivity of ballast and track drainage capacity has not been fully understood. Consequently, this study explores the effects of different size ranges and percentages of TDA on the permeability characteristic of railway ballast. To this end, large-scale constant head permeability tests were conducted on TDA-mixed ballast samples using a large-scale permeability test apparatus. In this study, three different TDA size ranges including 3 - 8 mm, 8 - 16 mm, and 19.5 - 26.5 mm and two different percentages (by weight), 10% and 15%, were considered. The experimental results showed that TDA reduced the hydraulic conductivity of ballast by 14% - 88% for the selected TDA size ranges and percentages. Subsequently, a 2D numerical seepage analysis was carried out to evaluate the effect of TDA on the track drainage capacity of a ballasted track. The seepage analysis results indicated that the track drainage condition of the ballast decreased from good drainage to acceptable drainage due to the application of TDA. The findings of this study could be effectively used to guide the careful selection of TDA size ranges and percentages for railway applications.