Shakedown Limit Analysis of Asphaltic Support Layers for Railway Slab Tracks

Shakedown analysis is a valuable method for assessing the cumulative deformation characteristics of ballastless track beds and determining the safety factor of longitudinally continuous structures under moving train loading. Asphalt support layers (ASLs) emerge to enhance track structure stiffness and prevent water penetration. Key design considerations include the influence of temperature on asphalt concrete strengths and the concentrated stress effect at expansion joints. To evaluate the ASLs, empirical equations are used, incorporating temperature-dependent modulus of elasticity and cohesion. Shakedown limits are calculated for various thicknesses and temperatures under two loading conditions: continuous structure and joint positions. The shakedown limit of axial load serves as an evaluation index. Research shows that at low temperatures, the critical depth for subgrade lies within the upper roadbed, with the nature of fills in this layer playing a crucial role in determining the shakedown limit of axle load for the subgrade. Above a critical temperature, the critical depth shifts from the upper roadbed layer to the ASL surface layer. The maximum allowable temperature is determined at the intersection of the design axle load contour and the temperature-dependent shakedown limit curve. To meet shakedown limit requirements beyond this temperature limit, increasing the asphalt thickness or fill strength of the structural layer within critical depth is necessary.