Ballast degradation and measurement of ballast fouling

In service, the ballast layer is subject to both deformation and degradation due to traffic load. Therefore, in order to keep the track performance within the required standards the ballasted foundation is subjected to various maintenance cycles such as tamping, ballast cleaning or reconstruction processes. A better planning of these processes warrants the extension of ballast life and the reduction of the maintenance costs. In practice, the extent of ballast fouling is usually based on visual inspections by track staff. Also, the current ballast fouling index does not realistically estimates the extent of ballast fouling. Therefore, ballast cleaning is not programmed as effectively as might be possible if a correct evaluation of the degree of ballast fouling would be carried out. The proposed paper presents the degradation characteristic of ballast layer and its effect on the ballast foundation performance is discussed. The shortcomings of the currently used ballast fouling index are then identified. Based on the analysis of an extensive number of field samples, a new fouling index was proposed, which properly quantifies the extent of ballast fouling. The classification criteria and the application of proposed ballast fouling index to predict the ballast-cleaning cycles is also presented.