5.4 Ballast spalls
Ballast spalls occur when particles of ballast become trapped between wheel and rail. Usually these defects are relatively benign and wear out, but in some circumstances they can initiate squats or corrugation. Some damage of this type can be avoided by ensuring that ballast is brushed from the rails after reballasting of track, but ballast can sometimes be picked up by the slipstream of the train. A small ballast spall is apparent in the photograph in Section 1.3.