Settlement Prediction of Subgrade Layer for Two-Way Track under Moving Train Loads

The present study proposes a simplified prediction model to obtain permanent deformation in the subgrade layer of a two-way track system under moving train loads. Two-dimensional numerical modeling was conducted to capture the dynamic response of the railway substructure, and field measurements from a one-way track on South African railways were used for validation. Thereafter, a series of parametric studies was conducted with varying track geometry and train parameters. The findings show that the subgrade behavior is affected by train movement on the adjacent track due to stress superposition. The results further reveal a clear relationship among subgrade deformation, the train critical speed, and the Rayleigh wave velocity. These observations were utilized to develop a new prediction model for estimating permanent strain in the subgrade layer of a two-way track, incorporating soil properties, track geometry, train speed with respect to its critical speed, and axle load. A distance correlation matrix was employed to quantify how axle load, train speed, and loading cycles affect the permanent strain. The permanent strain values from the numerical analyses were compared with the proposed model, confirming that the model performs satisfactorily for both one-way and two-way tracks. The proposed model accuracy was further ascertained by comparing its predicted permanent strain with laboratory data reported in the literature. Therefore, this study provides a user-friendly prediction model for estimating permanent strain in both one-way and two-way tracks for use by engineers for design purposes.