The maintenance of heavy haul railway lines causes considerable cost and in many cases difficulties to rail traffic. Railway infrastructure management in Finland is important because in many locations the same railway lines are used by both freight and passenger trains. Along with the mixed traffic, the cold climate presents challenges in keeping the track in good condition. There is a great demand for economical and non-destructive methods that provide continuous condition information of track structure. In recent years, the ground penetrating radar (GPR) technology for structure inspection has improved to faster systems and better data quality.This article presents the main results from a research programme that was aimed to identify different GPR-based railway ballast degradation classes and to develop a preventative maintenance planning system. An extensive reference sampling and laboratory analysis has been performed to aid in developing the GPR-based classification method for qualifying the ballast fouling. Classification is made by a fouling index, which is calculated from the frequency contents of the GPR signal. This quality classification can be utilized in the planning of undercutting programmes.

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At the moment, one of the most cost-effective ways to inspect a whole railway network for rolling-contact fatigue is to carry out an eddy current inspection. It has a great sensitivity to even the smallest near surface defects, but this can also be a downside as it can lead to indications of deep damage from an array of tiny cracks. This can lead to overestimation of damage severity. Moreover, sizing of cracks in rails is unreliable due to the large number of parameters that affect the eddy current inspection response. The depth of penetration is of major importance in eddy current inspection, since cracks that are over this limit cannot be sized reliably. Deep inspection is desirable, but it is unattainable in practice, since signal-to-noise ratio decreases while penetration increases. Also, deep inspection is more affected by variations in steel's electromagnetic properties. Furthermore, increasing inspection velocity will lead to decreased inspection depth. Most of the problems with eddy current inspection are related to the surface microstructure of the rail, and thus could be mitigated with a preliminary rail grinding. Therefore, eddy current inspection is best suited for maintenance quality control. However, eddy current inspection carried out with conventional equipment and without support from other methods gives only coarse estimate of the rails condition.

In Finland, the railway is a vital transportation system. A large quantity of raw materials, goods and passengers are transported on mixed traffic tracks. Due to freeze-thaw cycles, differential frost heave can affect the track performance and results in speed restrictions. The maintenance of winter-related problems on heavy haul railway lines is expensive and causes difficulties for the flow of rail traffic. In order to make maintenance cost-effective and sustainable it is essential to identify the problem areas and determine their causes. During the last decade the ground penetrating radar (GPR) technique has proven to be an effective and non-destructive method to measure railway structures and various material properties. This paper presents and discusses the key results obtained in a research project that studied the potential of the GPR method to locate track sections on Finnish railways experiencing frost problems and produce input data for preventative maintenance planning for areas at risk of developing differential frost heave. The GPR data, digital video and GPS coordinates, collected from the railway sections were combined with reference data and railway databases using the Railway Doctor software. This integrated data was then interpreted and analysed using multiple parameters specifically selected for the purpose of identifying the frost-susceptible sub-ballast structures and subgrade soils and defining the root cause of frost problems using the GPR frequency analysis techniques.

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