Life cycle and sustainability assessment of under sleeper pads for railway vibration suppression

Under sleeper pads (USPs) have been used as a resilient element installed underneath concrete sleepers to minimise dynamic loads onto ballast and reduce track modulus along the rail line. This paper highlights the effectiveness of vibration mitigation of USPs at various locations, such as rail joints, railway turnout crossings in urban environments. This paper is devoted to systems thinking approach, life cycle and sustainability assessment in resolving vibration problems using USPs. The economic service life span of fifty years has been selected as it is coincided with the majority of common design life for railway tracks catering freights, heavy haul trains, mixed traffics and heavy suburban trains globally. Based on assumptions commonly derived in rail industry, the life cycle and carbon footprint analyses under variant extreme weather conditions reveal that the vibration reduction materials in concrete sleepers seem to be an efficient method for mitigating track maintenance costs. However, it is found that the actual service life of the USPs, which cannot be determined by any international standard at this stage, is the key factor underpinning the outcome. In comparison with rail pads with economic service life of 10 years, it can be revealed that the track renewal costs using USPs can be excessive, considering the rapid rate of delamination problems (between UPSs and concrete sleepers), hydraulic abrasion due to moister entrapment in the interface, and wear of USP materials due to sharp ballast angularity.