Effects Of Fouling On The Stress—Strain—Degradation Behaviour Of Rail Ballast

Abstract

Ballast is most commonly used as a structural component of rail track due to its high load bearing capacity, resiliency and rapid drainage. However, ballast along coal freight corridors often becomes fouled due to spilling of coal from moving wagons, in addition to further track deterioration attributed to particle breakage and pumping of soft subgrade. Highly fouled ballast needs to be cleaned or replaced to maintain the desired track resiliency, load bearing capacity and the track alignment. In order to identify the risk associated with fouling, it is important to accurately assess the amount of fouling. In this paper, the use of Void Contaminant Index (VCI) compared to other mass-based indices is critically examined. A series of isotropically consolidated drained triaxial tests using a large scale cylindrical triaxial apparatus have been conducted on both clean and fouled ballast with varying VCI to assess the stress-strain and degradation characteristics. In accordance, a non-linear shear strength envelope for clean and fouled ballast is presented in a non-dimensional form. The maximum permissible train speed under different level of fouling is also proposed. Introduction When ballast is fouled due to intrusion of fines from external sources, significant changes in the pore structure of the ballast occur resulting in reduced particle interlock and diminished void ratio. Numerous studies on granular materials through discrete element methods (Huang and Tutumluer 2011, Lim and McDowell 2005, Lu and McDowell 2006) and specific examination of the behaviour of clean ballast using discrete and continuum mechanics approaches (Indraratna et al. 2011) have been employed in the past. However, detrimental aspects of fouling on rail ballast have still not been assessed in detail. In this study, consolidated drained tests were conducted using a large-scale cylindrical triaxial apparatus to study the stress-deformation characteristics of