The effect of coal dust fouling on the cyclic behaviour of railtrack ballast

Railtrack ballast particles degrade due to mechanical particle breakage, weathering and fine particles contamination. When the voids in the ballast are filled with finer particles, ballast no longer performs its intended functions properly. Ballast particles coated with fine dust, on the other hand, could potentially affect the stiffness and strength of the track structure adversely. This paper presents a study on the effect ofcoal dust contamination to the permanent settlement and resiliency response of ballast. Ballast was tested under a semi-confined condition in a large rigid cylinder. The test specimens were first compacted to achieve the level of field density and then subjected to axial compression loading. Displacement-controlled loading was applied either monotonically or cyclically. Monotonic tests were carried out first to evaluate the load penetration response of ballast specimens under the full lateral confinement. From the response diagrams, the penetration cycles were determined and cyclic tests were performed. The study has shown that the rate of accumulation of plastic settlement increases with the load cycles, indicating reduction ofballast resiliency. It is also found that the reloading stiffness increases with the increase in the load cycles. For the range of coal dust fouling levels tested, it is concluded that the fouling degree reduces both the resiliency and the rate of increase in reloading stiffness of the ballast.