Quantification of the effects of material properties and support conditions on under tie pad behavior

Recent trends in train operations have increased the loading demands on tracks for higher-speed passenger trains and heavy axle load (HAL) freight trains. These have led to accelerated degradation of track infrastructure components with higher maintenance costs, while also having less availability of track to conduct maintenance due to increased train frequencies. Under tie pads (UTPs), which are resilient materials attached under the crosstie, have been widely adopted since the 1990s as an effective method to mitigate track degradation. However, given that the performance of UTPs can be influenced by different characteristics, it is essential to understand the behavior of UTPs under various track and train operating conditions. In this study, the performance of commercial UTPs and generic elastomeric materials with different properties and characteristics were evaluated using four test support conditions that replicate the ballast interface behavior. The performance of the UTP was quantified and compared based on the results of static bedding modulus (C_stat), contact area, and maximum and average pressure. The result demonstrated significant variations in C_stat values under different support conditions, with an average of 314% for commercial UTPs and 712% for generic materials. Furthermore, the increased sample thickness of commercial UTP resulted in an average of 8% increase in contact area and simultaneous 10% and 6% decrease in maximum and average pressure for 0.04 in. (1 mm) thickness increase. The findings from this study can provide insight into how material characteristics with different support conditions influence the performance of UTPs, which can guide the selection of appropriate UTP types to achieve specific maintenance and life cycle objectives under various track and train operating conditions.