The shear resistance at the sleeper–ballast interface of a ballasted track is an important contributor in maintaining track stability under faster and heavier axle loads where the ballast undergoes significant lateral sliding. Different types of sleeper–ballast interfaces based on the type of sleeper arrangements, such as concrete sleepers, timber sleepers, and under sleeper pads (USPs) attached to the concrete sleepers influence the lateral stability of railway tracks. Therefore, in this study the shear and degradation behaviour of ballast at concrete–ballast, timber–ballast, and USP–ballast interfaces were examined in the laboratory using large-scale direct shear tests under 60 kPa normal stress. The use of waste materials in the construction of civil infrastructure is gaining a lot of interest in the engineering community. Therefore, in addition to commercial USPs manufactured using raw materials, recycled USPs manufactured from granulates of end-of-life rubber tyres were also tested in this study. The discrete element modelling (DEM) approach was used to predict the shear behaviour of ballast at 30, 90, 120, 150, and 180 kPa normal stresses. The bonded particle model (BPM) was adopted in the DEM to simulate the effects of particle breakage during shearing. The results exhibited that both commercial and recycled USPs significantly improve the shear resistance at the sleeper–ballast interface while reducing particle degradation compared to concrete and timber sleeper interfaces.

Ballasted tracks are being overstressed as the demand for faster and heavier trains grows, resulting in excessive deterioration, frequent maintenance, and increased life-cycle cost of the track. Therefore, advancements in track constructions, such as elastic inclusions, to improve track performance and minimize maintenance frequency while enhancing safety are imperative. This paper explores a critical review of various types of elastic inclusions used in ballasted tracks. Individual performances of popular types of elastic inclusions such as energy-absorbing rubber mats, tyre derived aggregates, waste rubber tyres, and polyurethane-based inclusions were identified from the literature, and recommendations for their use depending on field requirements were proposed. Many studies have confirmed the contribution of energy-absorbing rubber mats in improving the performance of both substructure and superstructure of the track, but further investigations are required for other types of elastic inclusions, mainly in terms of their impact on track superstructure behaviour.