A simplified approach for predicting the non-linear critical speed of railway tracks

When trains approach the railway track-ground critical speed ground deformations are amplified, potentially exceeding the linear-elastic strain range in the supporting earthworks. This leads to non-linear soil behavior which can be difficult to model due to high computational cost and the need for detailed characterization of soil properties. As a solution, for the first time this research presents a simplified methodology to calculate the non-linear critical speed of track-ground structures. The methodology uses a novel semi-analytical approach that combines dispersion curves with a simplified linear equivalent model. Using the approach, a track-ground static strain field is first calculated, and then converted into a dynamic one using a non-dimensional dynamic amplification function, independent of the elastic properties of the soil. The result allows the non-linear critical speed to be calculated using static simulation results which are relatively straightforward to generate. The methodology is validated using a 3D non-linear Hardening Soil-small (HSSmall) numerical model and then a parametric study is used to compare results for both concrete slab and ballasted tracks. The results show the proposed approach is a reliable tool for predicting the non-linear critical speed.