The effect of asphaltic support layers on slab track dynamics

The deployment of asphaltic support layers (ASLs) within railway track structures has the potential to increase track bending stiffness, assist moisture runoff and provide a platform for track construction. These merits have increased its usage within the rail industry, however the understanding of asphaltic track dynamics during train loading remains limited. Therefore, the primary aim of this study is the development of new knowledge into the dynamic behavior of concrete slab track systems enhanced with asphaltic underlays. To do so, a numerical simulation approach is used, comprised of two sub-models: 1) a coupled multi-body vehicle−track model, for the purpose of computing wheel/rail forces; and 2) a 3D dynamic finite element track-ground model to simulate stress wave propagation in the sub-structure. The models are validated using both analytical results and field tests, and then used to simulate slab track systems with ASL thicknesses of: 0, 0.05, 0.07, 0.10, and 0.15 m. First the dynamic response at locations both near and far from the track joints are compared to quantify the asphaltic foundation stresses, deflections, accelerations and strains. It is found that stress concentrations occur near the concrete base joints and are an important consideration for ASL design. Next, asphalt concrete durability at 400 km/h line speed is explored considering seasonal temperature variations and it is found that the expected cumulative damage meets serviceability requirements. Finally, the influence of different asphaltic layer thicknesses on reaction modulus is discussed, concluding that the optimal thickness range, considering plastic deformation and construction constraints, is between 0.07 m and 0.10 m.