Wheel/rail conditions and squat development on moderately curved tracks

Rail squat defects have been observed in railway tracks carrying either low or high speed trains all over the world for some 30 years. They can be found almost everywhere, and in most types of track structure or geometry. A rail squat is a subsurface laminated crack along the rail. It becomes a significant issue when the crack grows and the rail surface becomes depressed or finally chips off the rail, resulting in a rail surface irregularity. Such rail surface defects induce wheel/rail impact and large amplitude vibration of track structure. In Europe and Japan, rail squats have turned into broken rails. The root cause and preventive solution to this defect are still under investigation. In this study, some patterns of squat development related to curve geometry, rail profile and rail type have been observed, and squat growth has also been monitored for individual squats using ultrasonic plotting techniques. This paper presents the results of surveys and analysis of squat distribution vs different track parameters, as well as plotting of squat growth. It is found in NSW that there has been an increasing tendency for rail squats which have developed from rolling contact fatigue (RCF) on the high rail of moderately curved tracks (500m - 1500m curve radius). A case study on the wheel and rail profiles on the sections has been carried out to evaluate the influence of contact zones and stress levels on the propagation of rail squat defects. It is found that the squats' crack propagation is almost linear to the tonnage haulage. In addition, rail profile seems to have little influence on squat development over moderate curves.