A mechanistic-empirical method for the characterisation of railway track formation

Abstract

Abstract The measurement of track substructure deflections is an important parameter for the determination of structural capacity, identification of track problem areas and evaluation of overall track condition. This paper describes a mechanistic-empirical method by which elastic moduli of railway formation layers can be determined from substructure deflections under transient train loading. The method was founded on surface deflection theory from falling weight deflectometer (FWD) analysis. Finite element (mechanistic) analysis and field data (empirical) from railway substructure deflections obtained from multi-depth deflectometers (MDDs) were used to assess the validity of the mechanistic-empirical method by comparing measured and modelled railway substructure responses. The results indicate that substructure deflections and stresses are affected by the complex superposition of different bogie loading configurations on a particular superstructure. The load distribution in the railway substructure does not follow a 45° influence line as commonly assumed in surface deflection theory. On the contrary, railway equilibrium influence lines are significantly influenced by the structural capacity of the formation layers and in-situ subgrade. The predictions offered by this method strongly agree with the long-term formation peak strains measured by MDDs and this method was determined suitable for evaluation of formation structural capacity due to good agreement between measured and estimated elastic moduli of formation layers.