Efficient practices in railway ballast maintenance and quality assessment using GPR

The need for effective and efficient railway maintenance is always more demanded all over the world as the main consequence of aging and degradation of infrastructures. Primarily, the filling of air voids within a railway ballast track-bed by fine-grained materials, coming up from the subballast layers by vibrations and capillarity effects, can heavily affect both the bearing and the draining capacity of the infrastructure with major impacts on safety. This occurrence is typically referred to as ?fouling?. When ballast is fouled, especially by clay, its internal friction angle is undermined, with serious lowering of the strength properties and increase of deformation rates of the whole rail track-bed. Thereby, a detailed and up-to-date knowledge of the quality of the railway substructure is mandatory for scheduling proper maintenance, with the final goal of optimizing the productivity while keeping the safety at the highest standard. This paper aims at reviewing a set of maintenance methodologies, spanning from the traditional and most employed ones, up to the most innovative approaches available in the market, with a special focus on the Ground Penetrating Radar (GPR) non-destructive testing (NDT) technique. The breakthrough brought by the application of new processing approaches is also analyzed and a methodological framework is given on some of the most recent and effective maintenance practices.