ABSTRACT
This paper proposes an analytical trackbed design approach incorporating asphalt materials. The design parameters of axle loading, subgrade and trackbed material properties and performance requirements are detailed. The UK ground investigation for empirical trackbed design based on UK standards subgrade material classification is reviewed. A detailed assessment of trackbed material types is carried out and stiffnesses in both dry and wet conditions are assigned. The unbound layer stiffnesses and thicknesses are used in a multi-layered elastic model to determine the equivalent foundation stiffness for asphalt trackbed design. The trackbed stresses, stains and deflections under loading are calculated at critical locations. The results are compared with expected values of typical UK track bed systems to design the layer thicknesses. Case studies including feasibility of asphalt trackbed solutions over a wide range of existing granular materials and alternative trackbed systems to minimise new construction thicknesses are presented.
