Long-Term Behaviour of Padded Concrete Sleepers on Reduced Ballast Bed Thickness

Abstract

The positive effects of under sleeper pads have already been proven by track and laboratory tests worldwide. In Austria, padded concrete sleepers reduce track deterioration by 50 percent and have therefore been used as standard components since 2010. As the pads increase material costs, many infrastructure managers have discussed the idea of covering costs by reducing the ballast bed thickness. Technically, this approach (less ballast) is feasible, as the pads increase the track elasticity and protect the ballast. Further, pads lead to higher rail deflection and distribution of the load to more sleepers, and the stresses in sleepers are therefore relieved. Here, we compared Austrian test sections with padded and unpadded concrete sleepers and with a difference in the ballast bed thickness: standard thickness of 30 cm against 20 cm below the sleeper. Fractal analyses and standard deviations of the track’s longitudinal level provided information about the sections’ long-term track behaviour over 20 years. We found that the standard solution with 30 cm ballast performed better in the long term compared to 20 cm. Additionally, the test section with padded sleepers on a reduced ballast bed thickness showed a lower maintenance demand than the unpadded concrete sleeper track on a 30 cm ballast bed.

Track Deterioration Model—State of the Art and Research Potentials

“…Kuttelwascher [7] found that hard subsoil leads to higher stress in the ballast bed, whereas soft subsoil leads to higher stress in rails due to deformation in the subsoil. Furthermore, a recent analysis by Marschnig et al [24] showed that track segments with a 20 cm ballast bed thickness under the lower sleeper edge deteriorated faster regarding the track's longitudinal level compared to tracks with a 30 cm ballast bed thickness. In addition, track segments with a smaller ballast bed thickness were more susceptible to singular failures.…”

Assessing Average Maintenance Frequencies and Service Lives of Railway Tracks: The Standard Element Approach

“…If following the strategy to re-invest tracks always with the optimal component mix and to rehab subsoil in case it is necessary, the renewal demand decreases after the first renewal wave. The prolongation of service lives (e.g., due to padded concrete sleepers plus 25 percent [26,27] stretches the necessary renewals in the future (Figure 14).…”

Traffic Load and Its Impact on Track Maintenance

“…Improving track structure and installing innovative, robust components helps to drop the maintenance demands-much more than track-friendly vehicle concepts. Figure 10 shows, for example, the impact of using concrete sleepers with under sleeper pads [31,32] on the ballast-related maintenance costs (dashed yellowish bars) and on top, for example, a rail steel grade of R350HT in curves (dashed purple bars-rail grinding and rail exchange). The track maintenance cost decreases by more than 40% using these components in curves and still by one third in straight sections where higher rail steel grades do not reduce maintenance demands.…”