Ground-Borne Vibration Mitigation Measures for Turnouts: State-of-the-Art and Field Tests
Paper i proceeding, 2015
A state-of-the-art study on ground-borne vibration induced by railway turnouts (switches & crossings) is presented. Vibration generating mechanisms and possibilities for cost-effective mitigation measures are discussed. A brief literature survey and examples of results from vibration measurements performed by the Schweizerische Bundesbahnen (SBB) are presented. The present work was performed within the EU FP7 project RIVAS (Railway Induced Vibration Abatement Solutions). Mitigation measures for turnouts described in the literature mainly aim at reducing the dynamic wheel-rail contact force (impact load) in the crossing panel. This is supported by field observations of amplified ground-borne vibration at turnouts, indicating that there is a need to improve the design of these track components. A smooth wheel transition between wing rail and crossing nose is important to achieve low energy impacts on the crossing. Measures to mitigate the vibrations include the use of soft or stiff Under Sleeper Pads (USP) for better and more stable turnout geometry over time. The use of USP may also reduce the magnitude of vibrations transferred from turnout to soil. Other measures include improving the design of the crossing panel (material and geometry of crossing nose and wing rails) and the use of more resilient rail pads. Results from a Swiss test campaign at two different sites (Rubigen and Le Landeron), using stiff USP in four turnouts, are presented and compared to results from four nominal turnouts without USP. However, the vibrations measured at Le Landeron, and even more so for Rubigen, seem to be significantly influenced by the turnout and soil conditions. It is important to accurately determine the condition of each turnout to enable a meaningful comparison between the turnouts and to draw conclusions on the influence of turnout mitigation measures on vibration emission. The best approach to reduce the amplification of vibration is a system approach where different parameters (such as rail profiles, rail material, resilient layers) are designed to interact in a harmonious and robust way. It is thus important to identify the combination of parameters that defines the design of an optimum turnout. Modelling is required to optimize the wheel transition over the crossing panel. Further tests are needed to define the relevant geometric parameters influencing the wheel trajectory and the amplified vibrations. If an improvement of the dynamic wheel-rail interaction (wheel transition) can be accomplished that reduces impact loads on the crossing panel, both vibration magnitudes and the need for crossing panel maintenance can be reduced.