Deformation characteristics of fresh and fouled ballasts subjected to tamping maintenance

A number of train passes over time induces large settlement on ballasted railway tracks. Tamping maintenance application, which is practised worldwide, can lead to additional subsequent track settlement from the disturbances caused by the tamping tools. In this study, a series of model tests on a scaled-down ballasted railway track was conducted to examine the settlement characteristics of ballast subjected to tamping maintenance application. The particle movements during cyclic loading were tracked using a particle image velocimetry (PIV) approach to study the local deformations induced by the tamping tools. The results revealed that the intrusion of fouling material and subsequent maintenance application altered the settlement characteristics significantly. The PIV results revealed that the top ballast is loosened by the tamping tools. It was also found that the strength properties of ballast deteriorate with the fouling of the material. Notably, the strain hardening behaviour of ballast is weakened when the material undergoes 30% fouling or more according to the fouling index, FIp (i.e., an indication of degree of ballast fouling). The results of this study suggest that track maintenance should involve the tamping of fouled ballast before FIp reaches 30%.