Tram track stiffness measurement based on the vision method

One of the main parameters characterizing properties of railway track is vertical stiffness. Provision of its appropriate value is crucial from the point of view of dynamic interactions occurring in a wheel-rail contact, what in turn translates into vehicle running behaviour and safety, passenger comfort, as well as further degradation of track condition. Track stiffness measurement is a cumbersome process requiring expensive equipment and can be carried out only if the line is closed. The following research is intended to estimate tram track vertical stiffness by means of vision method which can be performed during regular tram operation. Track deflections of tram line in the city of Poznan were carried out using high-speed camera and further used for vertical stiffness estimation.

Degradation of railway track geometry – Correlation between track stiffness gradient and differential settlement

Based on the track geometry car recordings performed from 1999 to 2016 on a section of the Swedish heavy haul line Malmbanan, the vertical track geometry degradation is analysed for wavelengths in the interval 1–25 m. The upper layer of the subgrade on parts of the rail section is peat (depths of up to 2 m), while it is moraine on others leading to a significant longitudinal variation in substructure stiffness. The degradation rates of irregularities in the longitudinal level and the influence of track maintenance (tamping) on the track geometry are studied. In parallel, a method for continuous measurement of track vertical stiffness along the line, allowing for the detection of track sections with poor support conditions, is described and demonstrated. Synchronised measurements of the longitudinal level and the track vertical stiffness are evaluated to determine whether there is a correlation between a high stiffness gradient due to variations in substructure stiffness and a high growth rate of local track geometry irregularities. It is shown that recurrent severe local track geometry irregularities often occur on track sections where there is a combination of a low magnitude and a high gradient in the substructure stiffness. In such cases, tamping may not be a cost-efficient long-term solution to the problem. Instead, upgrading of ballast and subgrade layers should be considered as an option. It is concluded that measurement of track vertical stiffness is an efficient method for the maintenance planning of a more robust railway track, which also minimises the life cycle cost and environmental footprint.

On the Effects of the USP on the Lateral Resistance of Ballasted Railway Tracks

From the advent of high-speed (HS) railways and with increasing traffic-induced loads transmitted to the superstructure, maintenance costs due to track geometry degradation have become a crucial problem for researchers and railway administrations. Moreover, the operations of ballast renewal, track tamping, and track re-alignment, that are indispensable to guarantee a good track geometry, have dramatic effects on the tie-ballast lateral resistance, which in turn reduce the track flexural strength in the lateral plane and increase the proneness of railway tracks made of continuous welded rails (CWR) to experience either progressive lateral shift of the track panel or thermal track buckling phenomena. To restore proper values of the tie-ballast lateral resistance, railway technicians either impose a speed reduction or compact the ballast bed mechanically by mean of the dynamic track stabilizing machines. Recently, elastic elements in railway tracks are receiving more and more attention due to their ability to reduce track geometry degradation and to attenuate noise and vibrations. Under Tie Pads, or Under Sleeper Pads (USP), guarantee better homogenization of the track vertical stiffness and have received more attention due to their ability to reduce maintenance costs. Most published studies focused their attention to USPs’ attitude to improve track performances in terms of dynamic impact force mitigation and track quality improvement; however, with few exceptions, no available literature exists on lateral resistance of ballasted track with USP, and some question still remains whether or not the lateral resistance is improved by USP. In this study, the experimental results of about 40 lateral resistance tests carried out in situ are reported and discussed. The tests were performed with the Discrete Cut Panel Pull Test (DCPPT) technique on three type of concrete ties, with and without USP; each type of tie and the related track conditions (ballast thickness, subgrade thickness and composition, shoulder width, ballast wall, etc.) were representative of specific track conditions, namely traditional tracks, high-speed lines and gallery. The tests were carried out in loaded and unloaded track conditions, in compacted and just-laid track conditions. In compacted ballast conditions the peak lateral resistance due to USPs can increase up to 20% — depending on the material used — and this variation is almost constant in the bedding modulus range considered in this study, which was quite well representative of typical static bedding modulus values of actual USPs. Even higher advantages seem to be achievable with softer USPs in weak or just-tamped ballast conditions.