ABSTRACT
Track layers including ballast and subgrade degrade with repeated train passes, while this degradation can in turn affect the track critical speed as well as the dynamic stresses. This paper discusses a combined rheological-continuum analytical approach to estimate the influence of subgrade degradation on the track response. The track substructure with ballast, capping and subgrade layers are considered as continuum layers allowing the propagation of Rayleigh waves generated by moving trains. Representing mud pumping commonly observed in Australian rail tracks, empirical relationships capturing progressive degradation of subgrade modulus are adopted and combined with the analytical approach. Results showed that subgrade degradation is affected significantly by the dynamic stresses, while the critical speed is reduced. As the speed and axle load increases, degradation occurs at an increasing rate, propagating to greater depths leading to mud pumping. A new critical number of load cycles is calculated that will provide information on the length of the train for different axle loads and train speeds when travelling on vulnerable subgrades.
